SR250 Air Fuel Screw Adjustment
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- Опубликовано: 16 апр 2020
- In this video we take a look at adjusting the air fuel screw on the Yamaha SR250. We use the custom aftermarket Jadus air fuel screw, but the process is the same with the stock air fuel screw. It is just must easier doing this adjustment on the bike with the thumb screw. The other option is to modify a flat screw driver so that this is possible on the bike.
Jadus Custom Air/Fuel Screw is available here: modelikocaferacers.com/gb/jad...
You may notice in the video we needed to screw out the screw more than a half turn to get a reaction from the engine which is not what was mentioned in the video. This will be normal in most cases. The engine should be more reactive on the leaner side of the adjustments. You want to be a half turn away from relaxing the engine from a high idle.
As always, any questions, just shoot!
Cheers!
**UPDATE**
I realise now that this video is not very clear! Sorry about that. The video shows more what to listen for rather than how to actually set the screw. This is the basic goal:
The air fuel screw should be screwed in as far as possible without affecting idle, then backed out a half turn. This is the basic instruction that is mentioned everywhere and has been used for decades. So, start with your screw 4.5 turns out and start turning it in until you notice idle starting to pick up (this video shows what happens and what to listen for), stop there, then back the screw out half a turn. You are set!
Again, any questions let me know,
Cheers 
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I've only had the bike for 3 months. Built in 1982 and learned a lot from your videos
Glad we have been able to help man!
A friend of mine says that using a larger main jet means more fuel consume. My idea is that riding at the same speed and having the carburetor (original one in my case) adjusted like shown here, it shouldn't. I just think that with the mod you just simply have the chance to run faster (consuming more) if you like ;)
In which position is the needle position 3 is standard, but I had to hang it lower because it always ran too fat for me ... I find the new adjusting screw great
Standard for the SR is 2 turns out. But when you change the intake or exhaust you need to adjust. With the performance kit installed, we have a larger pilot jet and the screw is turned 3-3.5 turns out depending on air density.
Adjusting the carb, do you recommend changing the position of the needle to a lower position or just changing the jet and adjusting the screw shown here?
We would not recommend adjusting the needle position - that usually just moves the problem to somewhere else in the power band. The best thing to do is to get the pilot jet and the main jet just right, then adjust the air/fuel screw perfectly. Then you'll have a good set up :)
this is very good information, I am hoping to provide similar enhancement to my 1981 XT250. By the way, I would like the air filter and crankcase breather like that but I wonder how to get one that fits?
TheTechKey Hi there! Unfortunately the XT and the SR came with different carbs, so parts are not interchangeable. But the XT carb is supposed to be really good?! It has a pumper circuit for nice acceleration ;)
Hey there I put this KN filter on my 1981 XT 250 hope it helps still figuring out the right lean/rich level but make sure your gaskets are good too
www.amazon.com/gp/product/B00062YO8G/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Great video ,
i have question thouht ,if i use a non-vacuum fuel switch will carburetor work ?
O pateras soy Hi! Yes it will, as long as you block the vacuum port in the carburettor boot ;)
Just picked up a couple SR and a XT. Installed the XT engine in an SR frame. Runs sweet with the SR carb but now I'm curious about that XT carb and whether I should install that sucker.
I'm considering the header exhaust because the stock is puny on the SR and unfortunately I already sold the XT exhaust because somebody really wanted it$$. Have you any experience or had any customers with the XT carb and the JADUS header?
Hi Joey, cool you have both an SR and an XT! The XT header is better than the SR one yes. And our header is even better :) We are not familiar with anyone using an XT carb on the SR. We would presume you would gain bottom end power and throttle response (28mm venturi and pumper circuit) but lose out on top end performance (SR carb has a 34mm venturi but no pumper circuit).
@@JadusMotorcycleParts Cool Thanks for response. Then I guess I'll be that guy for now that experiments with it. Will get around to it after some other fiddling. Finish installing tank off SR185($60 wreck except tank i had purring in 30 minutes) Fits nicely in front but rear section will need modified. Temporary supertramp muffler(tuning disks👍) for test rides, then eyeball seat mock ups. Really like the extra zip it has over my TW200. Digging the videos. Very helpful
I just got a sr250 but I noticed if I rev the bike the revs stuck and doesn't go back down unless I turn the bike off. Any advice jadus?
It could be an air leak on the intake or a damaged diaphragm. We have videos on both of those things you should check out! :)
Hi. You said that screwing out the screw leads to a lean mixture.. but when the screw is positioned near the engine (instead of the air filter) when you turn the screw out you let more fuel to go, so it's reacher. I saw also on Mikuni manual and says like me. So, where's the error?
You are absolutely correct. This is a fuel screw, not an air screw. I like to call it an air/fuel screw to avoid confusion because the adjustment process is the same. But yes, screw out for more fuel (richer mixture), in for less fuel (leaner mixture). Sorry for the confusion!
@@JadusMotorcycleParts Glad I was useful. And compliments for the channel, is the best resource for Sr 250.
Hello again, thanks for the reply. Sorry if I bore you, but I need your opinion and your help.
Two days ago, after having cleaned the carburettor well, I started the SR250 after years of standstill. As I already wrote to you, in the PRI position for about 1 minute, gasoline flowed out of the air filter exhaust pipe. When I put the fuel cock to ON, the fuel stopped coming out, and the bike started easily even using full choke. Today, when I went to turn it on, inserting only the whole choke, the bike started up, after a while it went out and didn't want to start again, as if no petrol was arriving. Not even when pushed downhill did it start. I then put the petcock back to the PRI position, and after nearly a minute in this position, petrol was NOT flowing out of the air cleaner drain pipe like it did two days ago. I put it back ON, tried to turn it on and this time the bike started. What did you understand? Why do you think this happens, where is the problem? I think it is incorrect that after two days, you need to put the tap on PRI to start it. I repeat, I had the sensation that no petrol was arriving to be able to light. Help me understand where I need to intervene. Thank you very much.
The fuel in the float bowl must be going somewhere and emptying it. You should not need to use the PRI (prime) position every time you start the bike. It is only needed if the bike has been sitting for a long time and the fuel in the float bowl has evaporated, or you have just rebuilt the carb and need to fill the float bowl again. My best advise is to rebuild the petcock (fuel tap). It sounds like you problem is there. But it is always good advice to rebuild the carb on old bikes as well because I still suspect your float valve is not working correctly.
@@JadusMotorcycleParts Thank you very much. I will also be replacing the intake manifold as I have noticed a few small air bubbles when spraying petroleum jelly while the bike is running. One question: In addition to its "paper" seal, should a high-temperature sealing paste also be applied?
What front end did you use for the disk brake setup!
Hi Michael, this is the standard front end for the Spanish built SR250 models from 1995 onwards.
Question is the front fork from another motorcycle?
Excuse me, what should we look for then, that the engine runs the faster the better?
I apologise for the lack of clarity in the video! Take a look at the updated description :)
@@JadusMotorcycleParts Thanks. Now it's very clear (and at first I didn't read the description either, so sorry). I have a SR250 SE with a stock exhaust but adapted K&N air filter instead of the original (in the same place). I changed the position of the needle to be one position lower (so the needle one position higher) and I have planned to put a 125 main jet instead of the original.
BTW, won't you install a Kickstart?. I'm about to have all of the parts to install it.
@@FernandoelChachi Not on this particular bike, but on another one we have :)
@@JadusMotorcycleParts Hi. Today I've put the needle back to the original position and changed the main jet for a 125. I've followed your instructions but instead of listening to the revs increasing or decreasing I just watched the RPM's on the clock needle, and when closing the screw it finally raised to the higher revolutions, I then unscrewed it half turn. It works great without explosions as I was having earlier (a few) when increasing revs while going down a hill for example. As I commented I have a K&N adapted air filter with stock exhaust (I will surely buy yours in a time). To me, now I have more throttle than before, so to speak, more power on my hand to dispose ;)
Where is that clear tube going ( That one after the carb)
I found out its for the negative pressure vor the fuel Tap, my Problem is that my Aftermarket fuel Tap dont have the valve. My Problem ist that i cant find any fuel Tap Form the sr250 which have this valve. Has anybody the Same Problem? I think without the negative Pressure there is some Power lost
@@unknownuser8502 Correct! That tube is a vacuum tube running to the fuel tap - which only opens when the engine is running (creating vacuum). It even helps slightly pump fuel to the carb when the fuel is low. We would recommend trying to find a stock fuel tap on ebay somewhere, or, if you have another type of fuel tap, block the hole/vacuum line to the engine so it is not open.
I do know that nobody should move the idle screw (unless you know how it has to go). I've moved it from time to time. How the idle screw has to stay?. I mean: just touching the metal support, half of a turn, a complete turn more or what?
BTW, you do resume the whole idea about the adjustment of the carburetor in this video very clearly: "You want to be a half turn away from relaxing the engine from a high idle." You know that I've got different parts: an adapted K&N air filter, your improved exhaust pipe, a larger carburetor jet , your advanced timing set... and recently a different silencer, an expensive german stainless one www.motea.com/media/catalog/product/cache/a5bcf6e5787004a02b518212638fea9f/1/2/127230-04-1611138759-182628-0.jpg I've tried it as it comes and it was too loud. Then I tried a DB killer to get it quieter. I had to close almost all of the air flow and I found that I was losing power and having problems instead. Now I think that "I've got it", with a different DB Killer. Thinking backwards, it should had been easier just buying your exhaust, but well, it is working well now it seems, and I've also learned about how a different DB Killer (I've tried 3 of them) changes the noise there.
@@FernandoelChachi Excellent man! Send us an email if you have time and tell us about your experience with the different DB killers - we would love to know :)
We realised that the video is unfortunately not that clear sorry... we tried to help by explaining in the description of the video ;)
where is the battery?
i'd consider buying parts but everything in your store is empty
also it would be nice if someone figured out an air cooling scoop kit for the engine fins
would also be nice if there was a metal frame insert to remove the need for the air box to hold the side covers, i'd be installing a performance air filter and a fuse/relay box in the same area to add a few extra fuses with a diode and normal relay to mitigate the need for special rectangular relays, places i'd fuse are the ac line to the rectifier because i see them burning the plug on bikes, then the default circuit and then the lighting plus cdi, the mounted fuse box would also double as easy diagnostics once set up plus would clean up most of the wiring
Hi there! All of our parts are in stock and available for purchase from our reseller modeliko cafe racers: modelikocaferacers.com/gb/281-jadus-motorcycles
Extra cooling is best through an oil cooler rather than an air scoop. We developed an oil cooler and sold it for a while but only ran a limited production run. We also developed finned valve and cam covers that we have on our test bikes :) The electrics on these bikes is really simple so we have not yet needed to change much other than installing an automotive style fuse holder instead of the dated glass tube one.
@@JadusMotorcycleParts ah so this is the proper link for your site, i was going to the site that has your name on it
also i noticed something neat from newer bikes you could probly sell to make even better cooling, they make an adapter that goes over the oil filter cover to a radiator in the front with a check valve to prevent dry running but not for the sr250 yet, i suspect the part would be pretty simple and would afford even better cooling than a finned cover which would also help in hot climates, for a bike like mine the radiator clamps to the front frame bar, probly to the left because of the exhaust pipe.
as for fuses, the main reason i wanted to add a box was so i could branch it all to a main line and add in a main headlight and hazard switch being this bike always has the bulbs on which feels like a waste, added organised fuses would also allow a 12v socket to be added and i'd probly put that behind the seat padding on my trunk where the trunk release lock sits so i can charge phones, flashlights and other things i use on the road
i was also considering trying to find a better stator design that would fit the bike as i have been told the 2 coil type is kinda weak vs newer bikes and would let me have more electronics on the road without worrying about a dead battery, however i might just figure out a way to get even more efficient electronics instead as i'm sure they have ham radios that will just run off a small 12v source and i have heard the baofeng uv5r units have a battery delete kit for car use