PSA: Setting Mikuni carb pop-off on your PWC carb is essential to proper performance!!
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- Опубликовано: 28 июл 2024
- I've had a pile of PWCs recently come in that have run poorly, hesitated, bogged, even surged and stalled.
All of it due to the pop-off pressure being set incorrectly.
Some of the most clear information I've seen anywhere on setting up carbs on carbureted skis at Seadoosource:
seadoosource.com/carbreference...
seadoosource.com/mikunitests.html
seadoosource.com/carbadjust.html
Key things in video:
0:00 Introduction
0:42 Why setting the popoff is vital to proper performance
1:40 How the needle/seat and diaphragm functions together
2:10 Pump and how hoses need to connected be to test
3:12 Testing popoff
3:48 50psi popoff
4:23 Installed correct spring, ready for re-test
5:00 32psi with correct spring, dead on in the middle of the spec
5:20 Don't be a fool, test your popoff with the tool
Popoff tester I use: amzn.to/3hcVCK6
Links to products could be affiliate links, which earn me a small commission on your purchase for referring you, and best of all, it doesn't cost you a penny more! 
Авто/Мото
Some of the most clear information I've seen anywhere on setting up carbs on carbureted skis: trythistv.com/mikuni/
Popoff tester I use: amzn.to/3hcVCK6
Links to products could be affiliate links, which earn me a small commission on your purchase for referring you, and best of all, it doesn't cost you a penny more!
Wow, wish I had this knowledge in 2005, xl800 has always ran rough until 1/2t. After I rebuilt the carbs in 2005. Ffwd 16 years, and I rebuild them again - yet right this time! Thanks a ton!!!!!!!!
Its amazing the difference it makes, and the carb rebuild kits aren't exactly clear why there is a pile of springs in the package either.
LOL love your tongue-in-cheek approach to "PSA". No need to "apologize" when rendering such an invaluable FREE service-if anything more gratitude should be rendered to yourself and other RUclipsrs for such info.!! In other words, thanks, ha ha ha no need to apologize there, buddy!
That is the exact issue i am having with a ski! I will have to take a look at this and see if it fixes the low end bog!
Certainly worth a look!
I ordered that pressure tester, should be here Friday. I rebuilt my carb today and then took the ski to the lake and no matter what I did with the high and low speed adjustment, wouldn’t work properly and by what you said, sounds exactly the issue. I’ll let ya know how it works out. But regardless thank you so much for the information man!!!
Sounds good! Let me know what you find!
Can you post the link to the tester please?
You are a life saver. Thanks, Very informative.
Glad to hear that! Makes a huge difference in performance.
I appreciate this video my pop off was definitely an issue. neither carb was accurate. Where I ran into most issues is with accelerator pump"tiny little parts" and adjusting the arm and understanding how it works, i could not bench test the item. Good news is we are going out Jet skiing this week!
Glad you're able to get out riding! The accel pumps can be a real pain. There are ways to rejet and remove them entirely, reverting back to the older style jetting before they started adding the accel pumps.
Brap! It’s summertime where’s your pop off at! Great video
thank you!! this video just solved an enigma of how to test pop off.
it may also be the reason why my 3rd piston melted into a globule of aluminium and siezed the engine from a too-lean situation in only one cylinder of a gp1200r the other day.
Oh man thats not a good day. Sorry to hear about your GPs meltdown. Are you running premix or using the factory oil injection system?
If you've still got the injection system, you should give a good look at this other video I made about a serious issue with them: ruclips.net/video/5qpokTPiNoY/видео.html
@@trythistv yeah its running pre-mix. but there's a common issue where the back cylinder gets a leaner feed than the first 2.
undergoing a disassembly now to see if the crankshaft and push rod is OK or not.
and then might try to re-run the fuel line configuration after a carb rebuild so they all get an even share of juice (there is info about that on forums)... and if that doesn't work... maybe I'll sink it! hahaha
I saw your other video its very helpful!! thanks again
@@phildawe7172 You might try running a separate fuel pump from a snowmobile instead of the factory fuel pump (mounted internal on carb)
@@markcrandall7230 thanks for the tip. I'm in Australia so snow mobiles are rare as hens teeth. but maybe can consider some alternate bike fuel pump. etc thanks again
@@markcrandall7230 are you suggesting the pulse type powered by the engines vaccum? (quite cheap on ebay actually), or an electric powered fuel pump?
Gracias amigo saludos desde Costa Rica
Dude, Your a life saver. Thanks for video's 🎉❤
Glad to help!
I like to see more info on these Mikuni BN carbs. How to test the fuel pump. My Seadoo runs great for a few then dies as if it is out of fuel. Thanks for the video.
Air leaks are a huge problem with these carbs, as well as the old "grey tempo" fuel lines, they decompose internally and clog everything up.
I'll see what I can do on making another video as well!
Do you know the pop off pressure for a Keihin CDK-40 Carburetor on a 94 Kawasaki SS Xi 750?
I have a 1999 seadoo challenger 1800. One engine runs great at idle but won’t go over like 3k rpms at full throttle.
My other motor won’t start though. The only way I can get it to start is have the throttle atleast half way and it will start sometimes but then dies. Could the pop-off be the case?
Awesome video! I have a 2003 xlt 800. I have been through 1 engine and 2 top ends, I just replaced it with another engine, it keeps seizing pistons and I can't figure out why. I have done multiple carb rebuilds and have tested pop off. It ran real good last year with a black spring and 1,2 seat. It popped off around 60. However it seized a piston when going full speed for a longer period of time which leads me to believe it may have been running lean. I did not do a plug chop test on that setup to check my high speed and that may have been my problem. I currently have a 1.8 seat in there and 115 g spring as I am on vacation and only have 115 g springs and 80g springs to test with. I am going to try to put the 80g and 1.2 seat back in to solve the problem. The ski also ran away on me on the trailer with this setup so I am scared to go back to it. Any ideas on what could be causing my issue? Cooling system seems to be working and I changed fuel filter as well.
I'd do a plug read at wot, and see how lean it looks. popoff is specced to be around 50psi, the service manual shows a 1.2 needle with a gold spring (65g) which would put both carbs around 47psi.
Also, are you premixing or using the factory oil injection? can you ensure you're getting enough oil.
Also, is it the same cylinder siezing up on you every time? Rear cylinder?
Great video and explanation..... I just rebuild my carbs and my pop off is 23 per the spec. I cant get it up to 23, it pops at 20. Is that okay or doe is need to be dead on?
I would always prefer to see a bit low on the popoff rather than too high. You can adjust the lo/high screws in a tad to compensate for that much variance, but if its too high you'll never be able to screw them out far enough.
Also, ensure they are consistent across carbs if your machine has more than one, if they vary too much from cylinder to cylinder, its not going to be a good time for whatever cylinder is highest.
Thanks, I’m bogging out on 1 engine bettween 4500 rpm, do think this is ny issue but damn good info
Still likely a fuel problem, I've had a grand old time reading plugs to determine if its rich or lean, get out in a lake thats preferably calm, run right where its acting up for a minute or two ideally, then pull the lanyard without changing throttle position so it kills the engine. then pull the plugs, see if they're black, white, or a tanish color. if they are very black, its rich, very white its too lean, tan is about right, I will usually tend to aim for a little rich, especially if I'm tuning on a day where its 100 degrees, as the air gets colder the mixture will lean out slightly, so a little rich right now will be safe for all weather. It has worked well thusfar.
Awesome video. Love your glasses, what kind are they?
They came from Zenni Optical, I have a bad tendancy of getting gas and other nasty stuff on glasses, so I lean toward cheaper options, and these have held up fantastic!
www.zennioptical.com/p/mens-half-rim-stainless-steel-rectangle-eyeglass-frames/1631?skuId=163112
I do believe that link is to the exact frames I have, they are number 163112 if that helps.
I got the transition lenses because I work outdoors a lot and man having them tint automatically is neat as can be, they go light after a few seconds in an engine bay, and darken back up when I emerge from the engine bay!
attempted the pop off test on mikuni dual 44mm off an xlt 800 and it won’t pop off, pressure won’t go about 40psi, it just leaks out somewhere but i have no idea where, no bubbles in the oil i put in to test with
On a three carb setup if I'm getting 50 on 1 and 38 on the other 2 could that cause the two at 38 to run 10 degrees cooler and stall over 2500 rpm
It will certainly cause some funky behavior. The 2 at 38psi will run richer, which would tend to be cooler, and could flood out at higher rpm, while the one at 50 will run leaner, which would be hotter, I'm not sure what the spec is in your specific machine, but I would say it is essential for them to be balanced, or some real weird stuff is gonna happen.
Just rebuilt my BN44 carburetor on 92 Yamaha WRB650. Runs good at 1/4 throttle but anything more it misfires badly. The Mikuni rebuild kit had 2 springs, one shorter and one about equal in length to the original. I used the equal length one. Could that be the cause of the misfiring? I also replaced the arm which needed a little adjustment to equal the old one. Do you have any other reasons for the misfiring? Thank you.
I'd really suggest doing a plug read, ideally while it was misfiring, so in your case, take it out and run it somewhere above 1/4 throttle so it misfires for a minute or two, then shutting the engine off without letting off the throttle, then see if they look very dark (too rich) or very white (too lean), although you may just want to check the popoff with a gauge first, just above 1/4 throttle is right about where the popoff will start causing problems, I'd bet its not at the proper psi, those springs all look about the same to me lol, they're such a fine difference, just a few grams difference of pressure can make a huge difference.
im wondering if i can install one of these on a 650 motorcycle.... obviously ill need to make a custom intake manifold
I suppose in theory you could, not really any reason it wouldn't work, the main/only benefit would be it would work in any orientation unlike a traditional bowl style carb, which may be very handy if you're planning on riding in extreme angles often, such as wheelies or riding upside down... If you're going to ride upside down, Let me know, I'd love to see that 😆
I have a 96 Wave Venture 700 that will bog down on hard left turns only, but not at WOT. Thinking its time for a carb rebuild. i have heard about the "left turn syndrome" but i belive my bogging is engine power related.
Quite likely. Some machines do have a tendency to act different in turns, my understanding is it is due to the pump being loaded differently, the impeller and vanes in the pump are all angled, so turning a certain direction will put more load on the engine, but it should be barely noticeable, if its bogging down significantly, then I'd get ready to rebuild the carb. I did a video on that as well (ruclips.net/video/XmkVaZvP-48/видео.html)
and have some specs and stuff I'm working on my website: trythistv.com/mikuni/
i have a stock 2000 xl700 waverunner, i believe they are 38 mm? but not sure, would u know if that is the stock carb and the pop off psi for it? iv checked everywhere cant find specs
My Avon jetrib runs with the 2002 Yamaha xl700 two stroke. Ive got a low end fueling issue (hesitation), which I'm working on. After A LOT of looking (!) I found a service data sheet, 1999-2004 "Waverunner" XL700 (dame engine).
In short, it states Mikuni 38's, 67.5 low jet, front 120 & rear 130 high jets, l/s screws 5/8 turns out, h/s screw front 5/8, rear 1-1/8 turns out, gold spring (115), pop-off 55psi. I'm struggling a bit, stripped/re-built my carbs as per spec, but have to turn my l/s screws out 1-1/4 to get low end power. Any comments gratefully received! Hope this helps. Might try lowering pop-off as recommended here, then tune out subsequent rich-ness...
Great video, my question is I have this same carb and when I test the pop off the seat starts to come out too. What holds it in? I know there is a screw next to it but it doesn't look like it holds anything?
There should be a little u shaped bracket the screw holds down that clamps the seat into place.
Hi, I have a 96 gtx, runs and idles fine. Full throttle it bogs, or stalls if I keep the throttle down(wide open) I can keep it from stalling if I keep it at around 3/4 throttle. I've changed everything on this pwc. Any ideas? Any help will be greatly appreciated!!
I would do a plug read. It's a really awful experience but gives some great tuning advice. Here is what you do. Gather the tools needed to remove your spark plugs. Should be 13/16 socket and ratchet, put a life vest on, tighten the straps, remove the seats, launch the machine into a lake, and take off across the lake, find a nice long straight where there isn't a ton of traffic, and hold it right where the bog/hesitation is for as long as you can, ideally you want to run it for 30 seconds or so right where it's bogging, and then without letting off the throttle, pull the lanyard off, coast to a stop safely, and then remove the spark plugs, they will be flesh melting temperature so be careful, and then look at them, are they black and wet/sooty looking (too rich) or white and hot looking? (Too lean) from there you can adjust the high mixture needle in to lean it out a bit, or out to richen it up, I usually go 1/4 turn or so at a time and then feel how it runs, and adjust more as needed until it's as smooth and stumble free though the entire throttle range as I can get it.
Mine are popping off at 24psi (both carbs) but after they pop off one of the carbs leaks down to 0. Another RUclipsr said you should go down 10 to 15 psi and hold after the carb pops off. One of my carbs isn’t holding. Any recommendations?
Might be your needle and seat are worn a little bit, they have a viton tip usually, which over time can develop a small ledge and it may not seal perfect every time. It may not be a big deal in actual practice on the machine due to how the diaphragm and fuel pump work together as well as the vibration of the motor would likely jiggle the needle back into the ridge, but replacing them may be a good idea.
Do you have to remove the carb from the engine to test?
Yeah, it might be possible to do with it in the hull, but its sure a lot easier to do with it out and on a bench
Hello I have a 1999 xl1200 waverunner and I can't find the pop off specs anywhere. Also I tried to make them pop just to see what they where at and I couldn't get them to pop? Please help
I do believe 55psi is the recommended spec for that machine, sometimes they were set way higher, I've had some come into the shop that wouldn't pop with over 80psi pressure, way too hard to tune properly with it set that high, down around 50-55 will be much easier to get a nice smooth transition through the whole throttle sweep.
Thanks for the info.
Do you ever bend the needle lever?. Mine seem to be high and was flooding.
Do you adjust the arms height?
Does that effect pop off pressure?
Yes, you can bend the arm, it will change the popoff pressure, bending the arm up lowers the popoff, bending it down will raise the popoff, if you bend it too far up it will hold the needle open against the nub on the diaphragm and flood out really bad. I try to keep the arm close to level with the cavity it sits in.
@@trythistv
Thanks so much for the info. I did bend them up and it would flood real bad. Wasn't sure where the tabs should be.
Thank you
my 1989 waverunner 500 has a hesitation off idle. if I remember right it was 12 psi when I rebuilt the carb last month? do I need more pressure than 12 psi?
I haven't done much with the 500cc yamahas, I believe their carbs are slightly different, and typically run a much lower psi, I've heard 8-12 is fairly normal, you might try lowering it closer to 8 and see what happens, but again, I'm not well versed in the 500cc machines so I'm very likely wrong.
Do you have any specs for Waverunner 3? 650 with a sbn44
The popoff on a sbn44 wr3 machine should be around 50psi, 1 turn out on low adjustment, 3/4 turn out on the high adjuster screw, I always tend to aim a little rich (lower popoff, more turns on the adjusters) because too lean melts stuff, while too rich just fouls plugs and performs poorly, so it's easier in my opinion to adjust out a little too much richness until the bog goes away
thanks for the video! 95 Kawasaki jetski (i think STS) doesn't come with Mikuni carbs
You're absolutely right, some of the older Kawis has the Keihin carbs, Sometime in the mid to late 90s they evidently switched to Mikuni, because I had a 97 ZXI900 for a while that had triple Mikunis on it.
wave runner 650 starts and dies so i started messing the adjustments and now wont stat at all. Can you tell me how many times I have to turn the side needle from the tight position ? Thank you.
On a 650 Yamaha you'll set the low mixture screw at 1 1/8 turns out from seated, and the high mix screw also 1 1/8 turns out from seated. Idle speed set in the water somewhere around 1100-1500rpm (use something like a tinytach if your waverunner doesn't have a tachometer) and the popoff is specced at 25-35psi for that motor. hopefully that info helps you get it going good!
Thanks!!
Show!! Very good!
Glad you liked it! Thanks for the kind words!
Very nice video! Is there any chance, that because of this, PWC would run on ground while dry but not when in the water? All of the other sympthoms are the same
100% possible. With the pump loaded with water you've got a lot more drag on everything and if the fueling is all jacked up it may not even run at all.
@@trythistv thanks for your response! Subscribed 😉
Some Kawasaki came with Kehien carbs stock
You are absolutely right, I've only ever seen one or two of them, our lake doesn't have any of the neat older stand-ups or such, about the oldest kawis we see are mid 90s 900 and 1100 triples
Are you sure that this measurement is not made with the carburetor immersed in gasoline to best reproduce real conditions ? If there is gasoline above the needle I think the trigger value will be higher ? Thank you very much
Wouldn't change the pressure by that much, what we're essentially doing is setting the amount of vacuum that the diaphragm will open the needle, so the amount of fuel on one side or the other of the needle is going to be basically irrelevant, this is the procedure from Sea-Doo in the manual, and how I've been doing it for years now, I've never tried fully immersing the carb for this test, but I would imagine the pressure will be basically exactly the same, just it will be a lot messier.
Kawasaki Jet Skis started with Mikuni and after a few years went totally to Keihin (remember the Mikuni three screw?). Sea Doo used Keihin. I loved the Keihin because it mounted from the top, Mikuni mounted from the bottom. Keihin no longer makes watercraft carbs, ended in late 90's?
I do really hate trying to reach the nuts that hold the mikuni carbs on sometimes haha.
I see so few Keihin carbs where I'm at that I forget they're around, although I do have one on my Kawasaki SC project, though I may be swapping it out for a mikuni in search of getting more power out of that little 650cc engine...
Problem with the Kawa 650 engine, it was detuned from the factory. How? They put a 28mm carb on it. Replaced carb on numerous 650's with 38 Keihin off 720 Seadoo engine, they bolt right on, no jets to change, must bore intake and instant hp. My Jetmate had a single 38mm and R&D exhaust and impeller change, so much more power. Just like the pre 93 Yamahas, you couldn't hurt these engines. Kawasaki maid it simple and so much easier to work on. Look at Yamaha and how many pieces make up their intake and exhaust systems, what a pita. to work on. Love my 96 Blaster 2, 87 X2, 2005 800 SXR
More power is the last thing my SC needs, but its the first thing its getting after I fix the hull.
Then I guess I'll have to recover the seat and make it look half decent.
I appreciate the info, I did notice the stock carb seemed tiny compared to the 717 seadoo stock carb, which is exactly what I was thinking of putting on it. I wasn't aware they had used a Keihin carb on those, I've only seen Mikunis.
I rebuilt my carb replaced my fuel filter and fuels selector and now I’m not pulling fuel and when I feed the carb fuel via dish bottle the engine still doesn’t get the gas any idea what’s wrong
Does the engine fire if you squirt fuel directly in the intake? If it does then it has to becarb related. Pull the return line off the fuel pump on the carb and see if it squirts fuel when you crank the engine. If it does then there is a good chance your popoff is set wrong, if it's too high then the needle won't open and you won't get any fuel into the engine side of the carb, if you don't get fuel out of the return line then something is askew with either your fuel pump, pulse line, or the hoses between the carb and the fuel tank.
trythistv okay I got it too suck fuel too the carb and adjusted the pop off pressure into spec and it still isn’t getting fuel in the engine
I also remembered I replace the needle and seat too but everything seemed to move freely and the pop off is on the lower side too
Did you pull apart the entire carb? In the diaphragm area where the needle valve is where the jets are, they're under a little plate, there are some gaskets and such in there, essentially the intake suction should pull the diaphragm in which opens the needle valve which let's fuel into the chamber, where it can be pulled through the jets into the engine, it's possible a jet is clogged, or the high/low adjuster orifaces are clogged, you could unscrew the adjusters all the way and try blowing compressed air through to ensure they are clear, and pull the jets out, i use a little set of carb cleaning needles to clean jets out: amzn.to/2PhELKc
How do i find what the pop off pressure for a 97 yamaha wave venture 760?
I do believe it is 55psi on the 760 motors, I tend to have more success tuning out a slightly low popoff than trying to tune for a slightly too high popoff. If its dual carb, I'd aim to hit around 50psi on both (they need to be balanced, if one carb is more than a few psi higher or lower than the other one it'll act real weird)
@@trythistv thank you very much for the reply and the information.
Good morning. I have a yamaha GP 760. Was having to spray starter fluid in the intake just to get it to fire over. Was hoping maybe I had to run it balls to the wall a few passes around the lake to kill having to do that for every start up. That's not the case. Now I can't get her to fire what so ever. Fuse looks great. Replaced battery and spark plugs. I'm getting plenty of spark but absolutely no fire. Emptied the fuel filter and I'm getting plenty of fuel to it. Any idea. The spraying the starter fluid doesn't do anything now. Any advice sure is appreciated. I was thinking of ordering a rebuild kit for the carbs.
Having spark but not running on starter fluid is very odd. I would suspect carb kits are in your future but it should at least cough and run a little with some starter fluid or some gas poured down the intske
@@trythistv did a compression test and I was at 90 on the front and zero in the back. Poured some 40-1 down the spark plugs and she fired up. I'm rebuilding the top end . Took apart the carbs and cleaned them and it's not putting out smoke anymore. But boy is this a pain in the rear.
Oh man 90 is low, but 0 is a problem lol. I'd check your oil lines and all that, seriously think of switching to premix so you'll always know it's getting oil
Can I just use my old spring that of way will be set a factory spec??????
Yes! In fact I usually reuse the factory spring as long as it pops in the correct pressure range, No need to replace it unless it has become damaged in some way and is no longer at the proper pressure.
Can i use a vacuum gage (the mightyvac) to conduct the same test?
Yes, at least partially: it should work as long as it has a pressure mode like the model I have (amzn.to/3lKnx6E), with one major caveat, I do believe my gauge only goes to 25 or 30psi positive pressure and a fair amount of models require being set closer to 45psi, it could be possible to use a secondary gauge that goes higher and just max out the mityvac gauge and then keep going on the 2nd gauge though. If your Sea-Doo is one of the models that is around 20-25psi pop off then yeah, you'd be fine to use a mityvac exactly how I used the pop off tested pump. 1/4" poly fuel line works excellent on the barbed fitting of the mityvac too btw
Thanks bud i really appreciate your advice!
I'm going to be running my skis at altitude so they will be running a bit rich. My carbs are supposed to pop off between 36 and 60 and they are both just under 40. 36-39. Should I be ok?
Just because you are in pop spec, doesn’t mean there won’t be a hesitation. You still need to fine tune the low speed screw. Also, incorrectly set idle can affect the transition on the low circuit. You can do plug chop tests at each throttle range.
A little rich is better than a little lean in my book. You could have hesitation, or plug fouling at worst, while too lean you could melt pistons. Popoff is just one aspect of tuning these carbs, and can be adjusted around for the mostpart by adjusting the high and low speed screws. I'd take your machine for a quick spin at whatever lake you're headed to, and see how the machine feels, and if needed try adjusting low and high speed screws ever so slightly in, perhaps around 1/8-1/4 turn and re-test on the water.
Will they have trouble starting if this is wrong
It can certainly affect starting. if popoff is too high it could cause a lean condition where the engine just doesn't get enough fuel to start, and if popoff is too low it would provide too much fuel, fouling spark plugs and flooding the engine.
If you have more than one carb, some PWCs are dual or triple carb, and if they are not balanced it will cause some really strange starting and running behavior.
Edited: I am trying to tune a Keihin in my pretty stock 650SX. I measured the intake side of the carb at 34mm 1 11/32". For reference the airbox side is 41mm or 1 5/8". I have a 125 high speed jet and a 48 low speed jet. I'm trying to figure out my high and low speed needle jet settings as well as. It sayd it is a CDK carb, not a CDK II like i see online. I have no idea if it is stock or if it is even from this ski. Any help will be greatly appreciated. My pop off pressure is right at 30.
I suspect you may actually have a Keihen carb, but I may be wrong, a lot of those machines came with Keihen carbs, but sometimes they did end up getting Mikunis as upgrades down the road. My best advice is do plug reads and adjust as needed, around 30psi seems like a good starting point for the popoff.
I will usually tune to feel, adjust low and high in and out a little and do before and after thoughts, for example, turn low screw out 1/4 turn, does it bog or rev smoothly (on the lake), if it makes things worse, revert and try adjusting the other direction. and then tweak the high either in or out 1/4 turn and see if it improves top end or hurts it, and toss in a few plug reads along the way with all of this process, pull the plugs out and see if they look lean (clean and white), rich (black and sooty), or just about right (tan/slightly black but not fouling out with soot)
@@trythistv yeah, I’m not sure how I said Mikuni I guess it was on my brain. It is a CDK carb that measures 34 at the engine side but I guess it’s a 28…? On land I set the low end out 2 and top out 5/8. Doing a tune/ride tomorrow. Tonight in the dark with a headlamp I went to the ramp late and dialed in the low to about 2 3/4 out. I didn’t have new gaskets so that may be why.
As a side question if I go to a 44 mm carb and intake do I have to do with the pipe as well?
I have not personally done a keihin to mikuni swap, but I understand it involves either a new intake, or an adapter plate of some kind, possibly a different flame arrestor/air filter setup, as well as some modification to the throttle cable bracketry.
From a brief search, a good starting point should you do a 44mm mikuni sbn swap is 115 low jet, 140 high jet, 2.0 needle/seat, popoff at 20psi, 7/8 low screw, 1 turn high screw. But performance gain may not be immense without a pipe to open up the exhaust a bit.
Also, yes what you have is most likely a CDK34 (34mm) but it has a 28mm venturi, so the carb necks down kind of like an hourglass, goes from 41mm at the airbox opening down to 28 somewhere near the middle, then opens back up to 34mm where it bolts to the intake.
The 650 came with auxiliary pump style keihin cdk1 , the fuel pump is not built onto the carb itself. They will get the job done but finding a good single keihin 38 cdk2 will honestly make your life easier
Where can I purchase the pop off spring?
SBT has all the jets, springs and such you'd ever need: www.shopsbt.com/jet-skis/low_speed_main_jets_springs.html
Would you rebuild my carbs if I mailed them? 2004 yamaha xlt1200
I'd say it's probably a bad idea, rebuilding them and getting them properly tuned on the ski can be 2 very different things. They aren't too bad to go through, just basic tools needed aside from the popoff test tool
Kawasaki used Keihin carbs but awesome video
I've heard that. I've yet to see one though. We don't have many standups or super old skis in my area though. The only carbed Kawis I've worked on are the 900/1100 motors, which were all Mikunis if I recall correctly.
old video but does anyone know pop off pressure and high and low screw setting for 95’ wetjet duo 300zx . master craft only made the skis a few years and a manual is no where to be found .
replied to your other comment, I would try the specs for a yamaha 701 ski, I worked on one mastercraft wetjet and it was a yamaha engine in it so it might give you a starting point at least.
@@trythistv yes my ski also has the yamaha 701 , thanks for the advice much appreciated
How do I order a Guage like this?and whats is it called?
A popoff tester. The link is in the video description, or I'll copy it right here: amzn.to/3hcVCK6
I have a 1998 Seadoo Speedster 1800 with 2 Rotax 717 engines, I want to remove the stock fuel pumps and replace both of them with 1 electric fuel pump, my question is would the fuel pump need to put out 21-37 PSI? For the carbs to pop?
I'm not sure how well it would work, but you'd want a low pressure pump because the stock mechanical/vacuum pumps only produce a few psi. I would try something like this that should be around 4-6psi: amzn.to/3NJo8F1 and see what it does.
Make sure you plug the pulse lines that go to the crankcase on each engine.
And do some plug reads to make sure it isn't running lean. We don't want melting pistons.
@@trythistv 🤔 I wonder how the carb would build even 20 pounds of pressure, with a 7 psi electric fuel pump.
@@trythistv o and yes I agree, I’m gong to block off the oil pump & premix.
And hopefully installing some type of EGT sensor to prevent any lean conditions.
Testing the popoff is a little confusing, because that pressure reading is essentially telling you the spring pressure holding the needle closed.
The diaphragm pulls against the spring under engine vacuum, so testing the popoff is essentially in a very backwards way testing how much engine vacuum is needed before the needle opens.
As you do the oil injection delete you'll have to loop the rotary valve oil lines and make sure the RV cavity is filled with clean oil, there should be instructions on how to accomplish all that online.
I was just given two 2002 yamaha gp800r's that ran when parked 10 years ago.ive been working on one of them.had 150ish psi on both cylinders. I resealed the engine,flushed the gas tank, rebuilt the carbs and eliminated the oil system. Unfortunately i skipped the pop off test. I had to put the choke on slightly to go full throttle. My biggest issue was it seemed to load up on fuel idling. So i had to feather the throttle hear and there to keep if from stalling. I brought it home to play with the fuel mixture screws. WHAT A PITA. how did they ever expect someone to be oble to adjust it when the cards are buried under the exhaust ect. Is there a trick to it?
Guess ill be pulling the carbs to test pop off.
Any ideas?
The real trick to those adjusting screws is get rid of the "tamper proof" caps and replace the high and low adjusters with the t handle style so you can hit them with a super long screwdriver without removing the ridiculous exhaust, and also, you should make sure the exhaust has been properly serviced with the d-plate and temp sensor bypass chip.
The popoff is a very annoying afterthought sometimes. When you did the rebuild did you reuse the old spring under the needle and seat, or did you use one of the new ones in the kit?
@@trythistv i reused the old springs. I did buy a chinese carb rebuild kit. So i left the original equipment in there on everything that looked good. Like the plastic pump valves.
@@trythistv also i tried fin those t hanle screws but had no luck. Do u have a part number? They are 2002 gp800r
Ill be pulling them for pop off test today. Getting a mighty max pump frpm harbor freight
Edit the mighty VAC doesnt do pressure, just vacuum
Oh good, changing those springs causes more trouble than you'd ever realize. They send 4 different springs with all different rates and pressures, but they're all the same color (at least the kits I use are)
Here are some links to the T-Handle adjusters for your ski on a few different sites so you can use whatever one works best for you, as it turns out The GP800R (Also known as the GP800 A, has the 800cc PV motor) already has t handle low speed adjusters from what I understand, but this is for the high speed screws so you can adjust the top end mixture.
Jetworks Performance SA-100 (High speed adjuster)
ebay.us/40sWBM
amzn.to/3hr8D6b
You'd need 2 of them for your ski, one for each carb (4 of them total if you want to do both of your skis), and I know on the 1200PV skis the factory flathead adjuster is hidden under a press fit cap you need to drill a hole and yank out with a drywall screw (Or at least thats how I do it) and then you can remove the flathead adjuster and install the T-Handle screw.
Ty. Ordered the screws.
So after pop is it normal for bubbles like in vid. Mine pop at 32psi the stops at 28 psi but very small bubbles keep coming. But pressure doesn’t seem to pop. I also did 15 psi test and it hold all night. Are my needle and seat ok.
Yes, what happens is the needle and seat rely ever so slightly on being wet to seal. When you test the pop off pressure, you're blowing air through so it drys out the tip of the needle and then it'll bubble. If you relieve the pressure and wet the needle with some premix gas, WD-40 or something and it doesn't bubble until after it has popped then your needle, seat and oring that seals the seat to the carb body are all ok!
@@trythistv Ok thanks. You would not believe how many expert told me it need to not bubble.
Bubbled before the pop is bad, but you said yours holds 15psi overnight, which is wild, that's way more than I've ever tested a mikuni. Lot of people claim to be experts with years of experience but don't have a clue what they're talking about, at least that's what I've found thusfar lol
The pop off is an enrichment circuit that must be set to open at the correct throttle position. Best may I know how to say it.
Right! Its essentially a vacuum controlled enrichment device. when the vacuum pulls on the diaphragm it will add fuel. Pretty neat how they work!
New to jet skis but not mechanics and MAN, your videos have really helped a feller!!! The ole Google machine has failed me this time because I can't seem to find what my pop off pressure should be. Do you happen to know sir? 1994 Waverunner VXR 650 and a 1996 Waveraider 700. In the process of rebuilding the carbs now.
Both of those machines should be similar in terms of popoff spec, they both use a 1.5mm needle/seat combo, and should have 115g springs, which means 55psi is the spec for popoff, I do tend to set mine a hair below the spec and tune the high/low adjuster screws in a little bit, seems to make for a better running machine on every one I've done.
If you take your time and don't get frustrated, these things aren't that complicated, you'll be out enjoying the water in no time!
@@trythistv Hey man, I REALLY appreciate the reply!! I am learning that they are not that complicated and that these things are fun as hell to ride. I'm 38 years old and I've never ridden one till the other day. Lol!! Again, thanks for the help!!
@@trythistv Ok, what I'm calling pop off pressure is: When I start seeing WD-40 spit out of the needle and seat. Is that the correct way to judge that? If that is the case, mine is popping off at 19 psi which is way under the 55 psi. I've got a little digital regulator on it and I'm slowly turning it up.
So the way I test popoff is with a little hand pump gauge thingy, but regulated air can work just as good, your hose supplying pressure should go into the port that fuel would normally go into, has an arrow pointed "into" the carb, and you plug the other port that has an arrow facing "out" of the carb either with your finger or a piece of rubber and a clamp (I've had good success with the little vice grip quick clamp thingies and a piece of fuel line), and with the diaphragm out of the side opposite those nipples, where the needle, seat and arm are, spray a little wd40, or premix gas around the needle and seat, press gently on the arm a few times to open the needle and allow the liquid to lube the end of the needle, then apply pressure gradually until it pops open and sprays a shot of wd40/gas into your eyes, do that a few times until you're certain the reading is consistent, and that is your popoff pressure, you can change to a different spring to raise or lower the psi that the pop occurs.
If the reading is too much lower than spec it'll run rich, may bog, and foul plugs.
If the popoff is too high, it will be lean, hesitate (can feel similar to bogging from too rich), and potentially melt pistons.
You'll be able to see which is which on the spark plugs. if they are very black, thats rich, if they are very white and look like they've been hot, thats too lean.
I think I've explained that fairly well, if not, let me know and I'll try to reword it!
Здравствуйте,подскажите какой пиапсай должен быть на гидроцикле 760 RA 96г.Второй сезон чиню карбы толку нет ,запускается отлично газуется на холостых,как только спускаю на воду даю газу глохнет,менял ремкомплект не помогает увидел это видео может дело в пиапсае, как все это настроить?
Здравствуйте, я перевожу это с помощью Google Translate, надеюсь, все работает нормально, и вы понимаете.
Выталкивание карбюратора на двигателе yamaha 760 должно составлять 35-45 фунтов на квадратный дюйм, нижний регулировочный винт должен выворачиваться примерно на 1 1/2 оборота от легкого прилегания, а верхний регулировочный винт должен выворачиваться примерно на 1/2 оборота от легкого прилегания.
Hello, I'm translating this with google translate, hopefully it works ok and you can understand it.
The popoff for the carbs on a yamaha 760 engine should 35-45psi, the low adjustment screw should be around 1 1/2 turns out from lightly seated, and the high adjustment screw should be around 1/2 turn out from lightly seated.
I tried to test the pop up but I’m not able to hold any pressure? Is that an indication that the fuel pump gaskets aren’t sealing?
If you're plugging the outlet and have the diaphragm off so you can see the needle and seat then something is leaking somewhere, I've been known to put a little wd40 or something into the hose of the popoff tester and pump it up to see where its leaking out.
@@trythistvupon further disassembly I noticed there are no grooves for the o rings. I’m assuming it’s a knock of the guy got on Amazon or something. My guess is that’s the problem. I ordered a new carb..
What size is that hose? 1/4?
Yup, a lot of these use 1/4 inch fuel line, there is the odd one now and then, like the carbed seadoo 951s that use a 5/16 fuel line for the supply from the tank, and then 1/4 inch for the return, but generally 1/4 is the ticket!
Hello, do you recommend sizing up on the seat and needle size? I am rebuilding mikuni carbs on a gp1200 and the stock seat size is 1.2 with a 115g spring. Pretty high pop off pressure with that combination. If I sized up on seat size and lowered spring tension the pop off would come down but im not sure if this is good practice or not.
I just had an issue with a xlt800 (2 cyl version of the 1200pv essentially) where the carbs weren't synced well, I ended up dumping the 115g "gold" springs and switching to the black ones which I think ate 95g or 90g, but sticking to the 1.2 needle and seat, it dropped the popoff down to about 62psi, had to put the low screw in just a hair from the 1 7/8 spec but it ran flawlessly after that. I would rather have a slightly too low popoff without being excessively low though, as I feel it is better to be a touch rich on mixture and it's easier to close the low screw a tad to compensate for the lower popoff than it is to run lean and deal with that.
So in retrospect of my massive wall of text, either drop to the 95g springs or stick with the gold and move to a 1.5 needle and seat would be my preference personally. Make sure all 3 carbs are as close to even as you can get them, otherwise it'll do some real weird things.
You're supposed to be spraying a oil substance like WD-40 and underneath the needle so it can seal off easier and it doesn't leak because that will act as oil and Fuel and it will be much more accurate
I've always just used some premix fuel to keep the needle wet, Initially I tried a bunch of different fluids, wd40, etc but good old fashioned premix has always worked best for me, and I know nothing in it is going to harm any part of the diaphragm or seals because its the exact same stuff as will be in there when the engine is running!
I'm gonna tell ya lol kawasaki zxi 900 and 1100 don't use mikuni and it's weird the 1100's use a cdcv constant velocity carb and 900's use keihin cdk2 carbs which the cdk2 is similar to the mikuni but i have found them much harder to dial in
Is there away to get in contact with you outside of public comments.
You're welcome to shoot me an email tom AT trythistv.com, I'm not super quick at replying this time of year, I'm covered up with work for several weeks, but I'll reply when I can!
Why can’t you just bend the arm for fine adjustments? Like have maybe 40psi and need 35psi
That is one way to make adjustments, I have personally had some really strange results with bending the arm though, as it changes the position and angle the little nub on the diaphragm hits the arm, I'm not fully sure what all that would affect, but it caused me some weird behavior trying to tune a carb on the lake when I did that to get the pop off at the spec.
I've got a 2000 yamaha 800xl. It had a blown engine when I bought it. I've just rebuild engine top to bottom. Rebuild carbs with Mikuni kits. Took it out to lake and experienced the bog you describe in the video. Played with low speed jet settings with no change. When driving and it's bogging I give it a shot of fuel with primer and it will get past bog and perform well at higher rpm. Pulled carbs and checked pop off with 60psi gauge and they don't pop. Tried springs that were in carb prior to rebuild, which look same size to the ones that came in kit and still can't get to pop. Pulled carbs completely apart and confirmed kits installed correctly. I'm stumped. Any ideas? Thx
You could check what size the needle/seat combo is and calculate what the pop pressure should be from that (I have a helpful chart at trythistv.com/mikuni/ ), or you could just try changing to a lighter spring until you can get it to pop, Is the XL800 a PV motor or non-pv? You should have around 55-65psi pop pressure on a PV machine if my memory serves me correctly, tough to measure when its maxing out the gauge.
If you fool around and get them both popping at 60 where the gauge maxes out you may be in good shape since you've proven the bog you're experiencing is a lean bog because adding fuel with the primer will help it get past the bog. If it was a rich bog, adding fuel would make it worse.
I always do my tuning that way. If there is a bog/hesitation, give it a shot with the primer or pull the choke, if it gets worse, its too rich, if it peps up, its too lean at that RPM.
Don't forget to do a full throttle plug read too to make sure you're not lean up top. Terrifying to do, but once you've sorted your bog, take it out to the lake on a calm day, get to a nice straight section, run wide open for a good 30 seconds, maybe up to a minute or so, and then when you safely can, pull the lanyard without letting off the throttle. once you slow to a stop, pull the plugs out, they'll be hot, but look at the insulator and end in general and see if it looks black and sooty (rich) or white and like it was very hot (lean) or a tan-brownish color. With a 2 stroke it will generally be a little more on the darker blackish from the oil burning, but you can fine tune a little to where it isn't sooty and fouling out.
Lean is mean right up until you melt a piston, and then you'll wish it was a little rich lol
@@Trythistv It's a P.V. motor. New power valves and set according to manual. The P.V. module functioned properly by bench test. The seat is 1.2 and the Spring that came with the Mikuni kit is shinny silver which according to charts should pop at 67 psi. The springs in the carbs I removed were a brass color. So not sure if that's supposed to be gold or tarnished shinny silver. They look identical in size when comparing the two. I'm wondering if I may have a accelerator pump issue(I replaced diaphragm) or a fuel restriction. On hard suction the fuel is pulled through the restriction but at lower rpm it can't draw fuel. Just a thought. I appreciate your reply. What you think?
I'd put a little section of clear fuel line on the return path from the carbs to the fuel line and see if there is a lot of air, I've seen issues with air leaks on the suction side, such as the fuel filter, selector valve or other fittings cause some issues like this, but most often a bog like you're describing ends up being popoff or clogged jet or such, and of those two, I'd really try to get that popoff a little lower. You can trim the springs, somewhere there is information on that, clip off half a turn and its a few psi or something.
If I was working on it, I'd try to get them down around 60 and make sure both carbs are in sync, same popoff on both, and then retest on the water, that'll rule out things that you need to keep taking the carbs off for, which is a pain on the PV motors with the massive cat stuff in the exhaust.
@@Trythistv OK. Thanks again. I'll continue with springs. Is the difference between springs simply the lengths? The wire making the coils are the same spec? What I'm getting at is, are the wires thicker or tighter coils creating more resistence therefore increasing pop off pressure? Reason I ask is that all the charts I have seen reference the springs in grams of weight.
Right, grams is the amount of pressure each spring applies to the arm I believe. The length of springs varies, as does the thickness of the spring wire, so taking a spring with too high of a pop off pressure and carefully trimming a very minute amount of coil off can lower the pressure applied on the arm, which in turn lowers the pop off pressure.
Do they need to pop off together or separately. Then reinstall together
I'm not entirely sure what you're asking, if you've got multiple carbs, they need to be tested as shown in the video separately one by one, but adjusted as close to eachother as possible, you wouldn't want one carb to pop at 45psi and the other at 25psi, you'd have one cylinder very lean and the other very rich.
@trythistv thank you so much for the reply, so I set them at 32 psi both individually then put it back together and it was too high of a pop off pressure it’s still bogged, so then I reset them to the base at 23 psi perfectly on both and now it pops off beautifully and has no issues with bogging anymore. So what I’m gathering is, maybe the lower you set a pop off pressure a little more responsive it becomes.
This method was spot on, I looked at the range and the bottom of the range is 23 psi up to 35 psi for my specific Sea-Doo JetSki. Seems like the lower works better.
I do plan on adjusting the low speed and high-speed jets on the water a little more thoroughly to dial it completely in
@@ZLUVCRUCE I've always had better success setting the popoff a little low, essentially what you're actually doing is setting the point that the diaphragm will open and let fuel in, so a higher popoff will tend to make a leaner mixture, and a lower popoff will make a richer mixture. I find it easier to set the popoff low and adjust the mixture screws to compensate.
@@trythistv I set them both to 25psi
Now it’s much snappier
Still trying to dial in the low screws.
I just took it all back apart and completely rebuilt the carburetor it’s all new rubbers and plastics. And it definitely runs a heck of a lot better outside of the water but I’m gonna take it out later and test it on the water. I just looked up the factory manual and set the high and low screws to spec. So I’m sure I’m gonna have to do a little bit of adjustment on the water
Ty
Glad the video was helpful!
Em português ok obrigado fica com Deus abraso
I have a Kawasaki round body
MK - BN 44MM carburetor and I can’t find the pop off pressure specs anywhere to save my life. Wondering if anybody has come across them and would like to share with me lol. 😅
What kind of machine is it on?
@@trythistv 1989 Kawasaki JS 550 standup JetSki
Just an FYI not all watercraft use Mikuni.. Most all Kawasaki use Keihin Carbs. Similar in design but not 100% the same.
I've only seen the older twin cylinder kawis with Keihin carbs, which I have a quite unique 650cc kawi I'll be making some videos on soon, including the Keihin carb getting rebuilt, but that is a story for another day.
I've worked on a number of the triples, 900zxi, 1100stx, etc, and all of those have had mikuni carbs, I'm not sure if there was a cutoff at some point where kawi switched to Mikunis, as these machines were not modified.
I should start keeping track when I see any and make a chart on my website of all the different makes and models and what carbs they have.
Nope my '72 Buick PWC also uses a Mikuni
72 Buick you say? That's gotta be quite the machine to tow a tube with. Small block or big block?
@@trythistv 455 big block of course
This is why you cant just "use the silver spring" for example. You must verify the popoff pressure.
Absolutely! Do it right, do it once! The amount of carbs I see that someone rebuilt but used the wrong spring or something is amazing, they often need nothing but the pop off corrected. The tool isn't that expensive.
Where do you purchase a pop off hand valve?
I think I put a link in the description, but youtube has made it more difficult to find that now, so here is the link: amzn.to/3hcVCK6
(There may be better deals elsewhere, if you choose to buy from that link I'll get a small commission)
@@trythistv Thank you !
@@trythistv lol very small. i like your sense of humor. free shipping 2
@@mjm7187 lol no kidding, I'll get a few cents, but hey every penny counts :)
@@trythistv btw, found your video very informative, thanks!
Hi, great video. I found another video where the guy says that it should be 75 PSI on yamaha (ruclips.net/video/d5NtgmgPaH8/видео.html time - 7:45). I can't find the specs for my XLT 1200. If you could help with clarifying, would really appreciate
Geez 45 ! 19 is normal im pretty sure. Also you can cut some of the spring off and you can use WD 40 when you do this. If it’s boggin slap that choke and see if she don’t scream to life .
Some Yamahas do run 45psi or higher, but most seadoos are way way lower, I feel like 17-23psi is the range for a lot, I have all the Yamaha and Seadoo specs on my website too so that is very handy as a reference when rebuilding any mikunis.
I need to compile other brands info and get it all on there too.
Keihin's went on basically every Kawasaki watercraft I've ever seen. Mikunis went on everything else.
Very interesting! I know some had Keihins, I guess maybe it's just our lake, but we rarely see older skis, especially standups and such, as far as kawasaki's I've worked on a number of ZXI900, ZXI1100 and the 3 seater STX counterparts, and all of them had Mikuni carbs.
But even those are getting rarer and rarer, everyone is buying newer skis around here anymore so I don't get to play with the older models as often.
@@trythistv I should have clarified, I've only ever seen stand ups, the sc or the x2 from Kawi. Nobody around here ever buys the sit downs from them (at least I never see them on our lake). I guess my statement wasn't 100% factual.
Oh no no, your statement is perfectly valid, We both know Kawi did use Keihin carbs extensively, as did Polaris (boy those pwcs are even rarer around my area) We just don't many of the older skis and standups around here, which is kind of a shame because they were super cool, I always stop and stare at all the standups I see, really neat machines, and tons of fun too.
I should have perhaps worded it differently in the video and my reply to you that in my area I see Mikunis left and right, but not much else, I'm certain there are some real bizzare setups out there, I've been curious if there are any bowl style carbs rather than the diaphram type, seems unlikely due to how the fuel would slosh everywhere while riding, but who knows, I worked on a "Mastercraft" PWC once, very interesting, had a lot of Yamaha components, but finding parts for the proprietary jet pump and steering stuff was near impossible.
I greatly enjoy seeing what else is out there, always a great learning experience! And any time I can glean some knowledge is beneficial.
So bizzare that your lake has primarily standups and my lake has sit down skis, Thats pretty wild!
That's not true most Kawasaki had the Mikuni setup they did have a few with the others
@@shannonwilliams601 Which ones? I just haven't seen any I guess. 650s 750s sxr's etc etc etc.
😁👍😁
Soooo my airplane uses these carbs.... It's been either full throttle or idle lol thankfully those are the two settings I realistically use anyways. However.... I'd like it to be perfect. It's experimental and it's a glider that can takeoff on its own. So honestly even having an engine at all isn't really... Normal.
But I wanted to say thank you for sharing this. Where do I get the pump+gauge to check this? I've never seen a small hand pump with a gauge quite like that one.
If you're curious about the glider... The Soaring Channel
ruclips.net/user/TheSoaringChannel
I seriously am grateful to you sharing this. My needles were nearly fully closed before I ran ok off idle and going full power the needles weren't making much of a difference to the EGT I was trying to adjust.
I'm checking out your videos, man that looks like a ton of fun!
This is the exact gauge/pump I use: amzn.to/3XBH7pa There is a cheaper option, but the gauge only goes up to 30psi at max: amzn.to/3u1aKTn
I had a customer once ask me to work on his airplane after he had me do a few jobs and realized how meticulous I can be, I turned him down as its one thing to have a PWC or boat break down and leave you stranded on the lake than it is to have an engine break down and drop out of the sky. It sure did sound like an interesting adventure I would likely have enjoyed if not for the liability though.
Nothing but contempt for a poorly researched video. It should be deleted
I agree fully. We are talking about the baby shark video on here right?