Small Engine Repair: Checking a Vacuum Fuel Pump / Fuel System on a Kohler V-Twin Engine
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- Опубликовано: 6 фев 2025
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*Always follow the instructions in your repair manual when doing repair or maintenance work on Outdoor Power Equipment. Manuals can be found at the manufacturers website.
Checking the fuel system, and vacuum fuel pump on a V-twin 25HP Kohler engine involves checking the fuel lines that attach to the pump, and checking fuel flow. The first step is to check to make sure fuel can flow from the gas tank to the fuel pump. To do this, disconnect the fuel line from the vacuum inlet fitting on the vacuum pump. Take the fuel line and lower it to a point that is below the fuel tank and see if gravity will cause fuel to flow from the tank through the line. If fuel flows, than the line is clear. If fuel will not flow, than check the fuel filter to see if it is restricted. Also check the fuel tank shut off valve if the tank is equipped with one. The valve may be in the off position, or dirty and restricted. Check the fuel tank cap to see if the vent on the fuel tank cap is plugged. If the fuel tank cap vent is plugged than fuel will not flow out of the fuel tank.
Next, check the pulse line on the vacuum pump. Make sure it is connected correctly to both the vacuum pump and the engine crankcase. Also, make sure the engine is not overfilled with oil and the pulse line is not filled with oil. If the engine oil is overfilled with oil, than oil can make its way into the pulse line and block the pressure necessary to operate the fuel pump.
The next thing to check is the fuel line from the vacuum pump to the carburetor. To do this, take the line off and make sure the line is in good condition, and there are no restrictions in the line.
The final check is to make sure the vacuum pump is pumping fuel. Disconnect the vacuum pump outlet line where it connects to the carburetor inlet, and turn the engine over. If fuel flows from the vacuum fuel pump, than the pump is working. Kohler does not provide a more precise way of checking the vacuum fuel pump, and they say if you get fuel flowing through the pump when the engine is turned over, than the fuel pump is working correctly. Kohler does say the vacuum fuel pump should pump a minimum of 2 gallons of fuel per hour with a pressure at 0.3 psi and a fuel lift of 24 in, but they do not give you a method to check these specifications. 
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I had a ch 20 S Kohler V Twin, it was cutting out and shut off at high speed operation, I tried another carburetor, fuel pump, checked the fuel filter etc.(before watching this video) The engine idled fine all day. It was definitely a fuel starvation problem. After watching this video, it stated check the oil level. Well the engine I was working on had WAY to much oil in the crankcase. The oil level is CRITICAL to the operation of the fuel pump since it works off the crankcase. After draining about 1 quart of oil out, the engine ran PERFECT. If anyone has a similar problem check the oil level first. GREAT VIDEO!
You saved the day. You are the only person to mention the problem with too much oil affecting the pulse line. I had replaced my fuel lines, the filter and the fuel pump, but never thought to check my oil level. Sure enough, it my oil was a bit past the full mark. I drained it down to just below full and now everything works perfectly. THANKS!
Learn something new everyday. Never thought to check my oil level. Didn't know that that could affect the vacuum
FINALLY! After watching numerous videos. Finding one, yours, that actually addresses the problem I'm having. Your video may not fix my problem. But it gives me a great place to start. Thank you.
Excellent. No wasted time, no needless music, just the facts and demo. Thank You.
I expect this will be the same check procedure on my 22HP B&S with similar pump. Takes a lot of cranking but then it runs fine. New everything but Carb, pump and hoses..
Thank you. Your video is the first one I have seen that shows a comprehensive fuel delivery troubleshooting everything. Most focus on the fuel pump. Been chasing my problem and ended up being a clogged vent on the gas cap.
Hands down the most informed and to the point in layman's terms tutorial on the fuel pump. Thanks for "nothing but the facts".
10 years and Im just now finding this video?!? Perfectly narrated and illustrated. Very simple to follow along. Thank you.
Been working on fuel issue all day. Your video helped me within 2 minutes. Thanks a million!!
A great example of step-by-step, Point A>Point(x) troubleshooting. I use the same principle whether it's gas or electrical flow. Start at the source & test every junction in sequence until you find the failure. Once you've built up your knowledgebase, then you can start "most likely problem" troubleshooting. :)
And thanks for having your lighting set up well!
That was mighty helpful. I'll be out there at 7:30am using this method. Thanks loads.
Hey, that's gonna be tomorrow! I hope it went well for you! Thanks smallengineshop. Extremely helpful video!
Thanks for the great video! I recently rebuilt the Walbro carb on my 31F series 17HP Intek, and it ran great for a couple of months, then started acting up again. I checked spark, air, and fuel, and everything seemed fine, except that it would start spitting and sputtering after running for a while, and then sometimes stop. After a minute it would crank, and then go for some more. I saw 2:52, walked to the garage and opened the fuel cap, and was greeted by the hissing of air rushing into the collapsed fuel tank (it's hidden inside the frame of the mower) and a loud pop as the tank flexed back to it's normal shape. That little diaphragm actually pulls hard enough to collapse a heavy plastic tank! The engine starts and runs fine now with the cap partially opened, I'll have to replace that soon. Anyway, thanks again, your video saved me from tearing my hair out!
As many others have said, nicely done. I'm checking my fuel pump tomorrow. It runs when I drizzle gas into the evaporation chamber before the carburetor. If the fuel pump is not it, it's probably jets, also simple.
Nice presentation of the troubleshooting flow chart! I went at it from a different approach,based on my personal mechanical knowledge, but didn’t think about the possibility of the crank case being over full causing this issue🤯. Thanks! That’s the first thing I’m going to look at tomorrow morning. I’ll be back with a comment,if my problem is solved by this inspection.
Thanks for explaining the different openings on the fuel pump. Had hoses wrong. Fixed now. Much appreciated
Yes, he had the oil overfilled and the rubber vacuum line to the pump was cracked in half and deteriorating from oil in the tube i suppose. Replace that vacuum line to the crank case if needed. Thanks.
I'm usually critical of video's but this one is great. Thanks for not having any wasted time.
Thanks for the video.I see a lot of people asking why take off the air filter assembly. I’m glad you did! My was already off and I was ready to buy a new fuel pump.I am working on a Honda GX610 and it keeps cutting off starving for gas. Now I know the lines, filters, and fuel pump are all clear and working properly, I KNOW now to keep searching for that low oil sensor. I’ve bought a new one but can’t find the one on the engine.Anyway, Thanks Again!
Excellent video and well put together. Outstanding camera work as well as a concise and succinct commentary. Wish all DIY videos were this good! Great job!
Thanks
Nice job, thanks. Excellent camera work, tool selection and narration!
As others have mentioned, could troubleshoot in a way that avoids air filter removal, but it's always good to have a visual check of the entire fuel line and carb.
Those notes: (thanks wonka & quantumrift)
1. Vacuum gauge is a good, inexpensive tool to help with troubleshooting
2. Can remove fuel lines from fuel pump line to save time and add a small piece of spare fuel line to do checks, if fuel pump is fine, then you know it is a line condition issue or obstruction
3. If gas cap vent is an issue, a tooth pick can be the right tool for a fix
Any votes on how long most fuel lines last before their condition affects performance in hot, humid climates? 3, 5 or 7 years?
Excellent video, very thorough.
Thanks!
Great video...I tested my pump as shown in the video, and everything worked as shown, but my problem continued, the engine would start up fine ...but only run for a minute or so, then die (as if it ran out of gas). Letting the engine sit for a while would then allow it to start up again for a minute or so. I watched a couple of videos and one video mentioned how you could tell if the pump was old by checking the small screen on the front of the pump....if it was black it was "old" if it looked metallic, then it was "new"....hmmmm I wonder?....so I got out some alcohol and a small brush and cleaned the screen from the outside (it was black and dirty) ....once cleaned the engine started right up ( as usual) but insteadf of dying out I mowed the entire yard with no further issues (about a 40 minute job)....so you may not even need a pump at all....you may only need to clean the small screen....worked for me !!! Give that a try !!!
Thanks for that tip.
How is your machine running this year? ,i jave tried everything so im gonna try the screen cleaning next after reading this
My problem on a 22HP Kawasaki in my X320 JD turned out to be a bad connector (12 Socket) with 3 yellow wires. One of these had low (10VDC) and was not opening the Fuel Shut Off Solenoid. I checked the solenoid direct from Battery. I went at the Connector (very small connectors) with Brakleen and plugged it back in and heard the Solenoid click. I had started at the solenoid checking connectors and voltage. There are 2 other connectors. One 5 pin, one butt connection at engine.
This after pulling the carb twice, blowing out line from pump to tank, replacing Filter, Fuel Pump and a lot of beer. Works perfectly now.
Thanks for your clip you just saved me a ton of money thought the fuel pump was stuffed mean time it was the gardener over filling the mower with oil
Thanks for watching
Best 8 minute video on V Twin fuel system's DONE!!.. those long 15/20 videos Chit Chat drive me crazy.. again thanks for the informative video...
You so right! I hate that!
One thing you missed is that some tanks have a wire mesh screen mounted to the pick-up inside the gas tank, these can become plugged or actually collapse and restrict gas flow. This happened to my Simplicity it would idle but was not getting enough gas to run at higher rpms. After removing screen and installing a good inline filter the tractor runs great.
Nice. Thanks for the walk through!
Great video, lots of usefull information and no wasted time talking about crap that has nothing to do with mowers. You should teach a class on how to make videos for RUclips about mowers. There is more useful information in your eight minute video than I have found in hours of other videos. A lot of people that post videos about mowers waste so much time doing ignorant crap that I turn the video off before they ever get to anything useful. And yes, Taryl fixes all, I'm talking about you.
This video was very helpful. Why would some ‘dislike’ the video
Well done. Thanks.
That is MY mower. I bought it for $100 cause the owner didn't know how to change the $12 PTO switch.
I removed the deck, and just buzz around the 9 acres with it since it has a fast forward speed.
SIDE NOTE: Dig around your garbage and find a tin can that doesn't have sharp edges.
As usual...
THanks for THinking!
A very common, but not well known at all, reason for bad flow from the vacuum fuel pump to the carb is air in the gas line somewhere between the gas tank and the fuel filter. The line isn't "plugged" with dirt or debris. The air simply prevents the relatively weak vacuum pump (even when new) from being able to suck a sufficient quantity of fuel through the system per minute. Most often what happens is that the user runs out of gas, or gets to the point where then engine is sputtering from being starved. Gas is put in the tank, it starts, but air may be hiding somewhere in that long line on a zero turn. After 10 to 30 minutes it cuts out. Solution is simple but not OSHA approved. Blow into the gas tank while your face makes a tight seal so pressure builds up. This will clear out the line. (By the way to test a fuel pump just blow into its plastic tube that is ordinarily connected to the valve cover. If it totally resists you blowing into it, it's likely still good. This video explaining this which I found today was a revelation. Won't be buying an annual fuel pump. ruclips.net/video/eQf1BDmyUCw/видео.html
A vacuum gauge is a handy and cheap instrument to have around. I would have checked the vacuum inlet first with a vacuum gauge. THEN, instead of disassembling the air filter assembly, just unhook the outlet line, and stick a piece of fuel hose into a can. Saves about 5 minutes, and see if it's pumping fuel. It can also be checked with a pressure gauge on the outlet. As for the fuel cap, all you have to do is ensure that the pinhole vent hole is unclogged. I have a John Deere 345 and it wouldn't start. I pulled the fuel cap and found that over 13 years of use, the vent hole had become clogged with debris and air does flow into the tank due to the vacuum. A toothpick cleaned it out in about 10 seconds. No new cap needed.
my vacuum pump doesnt see to work
Good video 👍 precise and to the point. Kawasaki fh 641 v have you ever heard of the fuel pump being relocated because the mower manufacturer put the muffler to close and causing vapor lock. This is on a snapper zero turn mower that none of the half dozen small engine shops in my area will work on. One mechanic told me there was a recall but nobody works on snapper because they don't pay the shops when they perform warranty work. The mower starts great when cold and will not start when hot
I checked fuel flow rate before by connecting separate fuel source to Ron the engine with variable pressure electric fuel pump. For example, 2 gal pet hour would be 16oz (2c.) in 3 min., 45 sec.
Let the engine run off other fuel source, pumping fuel into a measured container. Don't forget to start your timer when the engine fires up, and SECURE THOSE FUEL LINES!
Very well done. Most on RUclips are not watchable due to such bad video. Yours is very professional looking and informative. Thanks.
Simple and straightforward!
Excellent video! Well photographed, showed all parts perfectly, great commentation with a very good description of just exactly how to check the pump to be sure of good working order without too much useless vocabulary. Even telling me the size socket to use! Thank you for putting this here!
Thanks
Good clear and concise video. You instill confidence. I have a craftsman mower with a Briggs & Straton 18 HP OHV engine that will start well then after an hour or so it dies. The battery has just been changed to a new one but like I said the engine stopped after about an hour of use. This has been happening for a couple of seasons now. It is very temperamental.
Thanks
smallengineshop ive got a ? Could u email me i have this motor in a 20 hp and cant get it started ive had 3 engine shops look and none can figure out y it wont start
Mine is occasionally spitting gas out the two small holes on the back of the pump. It did it once before, maybe last fall Nov ‘23. I ordered a pump but the next day it didn’t do it and it hasn’t done it again until today June ‘24. I assume it’s a diaphragm or gasket or seal or something, just odd it doesn’t do it constantly.
Thanks for the information. My father has a Kohler engine that is having problems but, I wasn't sure how to verify the operation of the fuel pump. I wasn't sure if the pressure was high enough. From what you said, it appears that the pressure isn't as important as the fact that an ample amount of fuel is flowing. I'll now focus on the carb float etc.
Thanks again.
THANK YOU. for this Video. God Bless You>>!!
So I’ve already done all of that and I’m not getting vacuum FROM the engine.
What should I look for? I’m going to check the intake manifold for cracks and looseness.
Is there some sort of internal diaphragm?
Thanks for any help anyone.
One of the best videos on RUclips! Thanks!
Excellent and thorough. Brief and clear, thanks!
Well done, thanks! I don't have a Kohler, but I can use these principles to check my fuel pump.
SpockMcoy Issmart Thanks for watching!
Fatboy, look at the lines. I've noted 3 on any I've worked on. 1 is from the fuel tank, 1 is out to the carb, 1 goes up into the engine, where the vac is drawn from. hope this helps.
I have a john deere 160 lawn tractor that doesn't get any gas to the carburetor. I replaced the fuel pump and it went around the yard four times and then sputtered and quit. If I put gas in the carburetor it'll run and the gas is coming out of the fuel line from the tank If I take the filter off. If I turn it over now I don't think gas comes out of the fuel pump.
Question for you: Should there be fuel flowing out of the pump without the engine running/cranking? Or would that be a sign of a bad diaphragm?
You would probably have some pressurized fuel in the line (as you did), but should it continue flowing once the pressure is relieved?
Having issues with fuel flowing out of the throttle opening on the carburetor after sitting overnight. Already took apart and cleaned the carb and float bowl, and that helped for a while, but still having the issue.
Thank you for the informative video!
I like the way you make these steps simple and helpful, step by step to eliminate and find problem, good job.
I would have first checked the vacuum side with a VACUUM gauge first.
Much appreciate you posting the video and documenting the troubleshooting steps well. I've not dealt with a vacuum fuel pump before and this helped with some of the diagnosis of a tractor I'm working on. Thanks!
I have a new pump, lines are clear, new carburetor. Seems like I am not getting enough vacuum suction. It that a sign of anything else? Thanks. Great video
This is an old video but hopefully I'll get some answers. What would cause me to get no vacuum or pressure pulse on the pulse line from the engine to the pump.
No cracks in the hose. Oil level is fine. Don't see any cracks in case.
Possibly a valve problem or head gasket ?
Thanks, checking a motor fuel pump on a Hasquavna ride on mower, this video great, so clear!
If you have a test gauge fuel pressure runs from 1 p.s.i. to 2 1/2 lbs. depending on r.p.m. Even ultralight airplanes and some Japanese motorcycles have a pressure range like that using a pulse pump.
Hi. What is meant by positive and negative pressure??? Positive pressure the engine is sucking from the pump and negative pressure means the engine is blowing into the pump? Plse explain. TQ
Thank you for clear explanation of workings.
You are welcome!
I thought the same thing, could the diaphragm be burst and let fuel flow through?
Hi again. Another question: if you are not cranking the engine but the fuel still flows out, does it indicate that the fuel pump is faulty since it only pumps out fuel when there is a pulse? TQ
How to check the pulse line? Do you have to remove valve cover?
Hey just wanna let you know you did a outstanding job you’re to the point and explains it very well. Thanks for your help
Thank you for a great video, I will definitely follow all you steps and am feeling up to the task. You have great patience and remarkable calmness (a trait we would all love to have) when gas started coming out of the hose toward the end of the video.
Sorry 1 more question: my scooter has a one-way/no-return fuel valve installed between the fuel filter and the fuel pump. Why is it necessary? And does having a no-return valve helps to solve the problem of a faulty fuel pump that has fuel coming out even when there is not pulse from the engine? TQvm
Got gas maybe lots of it in your oil? This is a good place to start.Mine pumped gas OK and it poured down the vacuum line into the oil crank case found out by taking the vacuum line off at the crankcase. Can be checked by applying no more than 5 PSI to the gas inlet and plugging the fuel outlet. Would run for maybe 3 seconds black fuel rich smoke stained the grass acted like it was starved and flooded simultaneously.
How did the engine start when you put the knew pump if the carb didn't have any fuel in it?????
Great video. I got lucky and loosened the fuel cap (JD X300) and it started. Checking the pump would have been my next step though.
Good vid. But could have just taken the outlet hose off the pump to check the pump flow. Then if you have flow, move to carb. Step one, make sure there is fuel in the tank. Step two, check for spark. Step three, check fuel pump (if the engine has one) Step four, check carb. Start with the source first, whether that's a fuel issue or spark issue. Don't mean to knock your vid, just an easier route to the same result.
Good vid dude ......I have to tackle this tomorrow. Im getting fuel TO the filter,thats all I know so far. And I do know the fuel line FROM the filter to the pump is "aged" with slight crtacks etc but no leaking ......and the line FROM the pump TO the carb is very aged & it even feels almost britle when I try to smash it with my fingers. Hoping iots my Line & Not my carb.,
+97warlock ismyname UPDATE.....Ive removed fuel line from Pump to carb & NO fuel. SO someone on youtube said "oh just remove the 4 screws & it comes right off". I did this & the only the front half of the fuel pump comes off. Now Im stuck in limbo wondering how to get the remainder of the pump off there. All I see is a plunger type diaphram flat thing. - Thinkin of mounting a Manual pump.
very informative, educational video. Thanks for the clear, concise, no nonsense presentation.
I’ve been searching for this. Thanks.
May i ask everyone, is it possible that the fuel will flow thru vaccuum fuel pump when the engine is not running? What is the problem if the vaccuum fuel pump continouos discharge of fuel even the engine is off?Thank you
Good video. I think my pump is bad. Engine starts with starter fluid but dies. I have fluid from filter but not past pump. Better this than fuel slinoid.
Question, are these supposed to cut off fuel when there is no vacuum applied?
I bought a replacement that just flows right through from gravity.
I have a 2001 2 stroke jetski with fuel problems. and I've narrowed it down to either the fuel pump or the vacumn line. Last thing I'm wondering is when I feel turn the engine over with the vaccumn line off the pump it's only blowing air shouldn't it be sucking?
Some fuel lines coming from the fuel tank (depending on which model) Will enter from the top of the tank instead of the bottom and it just dribbles out of the fuel line when removed at pump, even when held close to the ground.So keep in mind, Ive used a hand pump with a light draw on this line to verify this passage.
Never seen a fuel line coming from the top of tank. That defies gravity. I could be wrong! Any way I have a small funnel that just covers the tank filler opening. After disconnecting the fuel line from the pump and inserting it in an empty container I cover the filler inlet with the funnel and blow a VERY LIGHT I repeat VERY LIGHT air stream through the funnel into the tank to push any obstruction threw the gas line. you can see the tank expanding slightly with air pressure. This ensures for sure, nothing blocking fuel line from the tank. CAUTION: I said a low pressure of air. You do not want to explode your' fuel tank just push any obstruction in fuel line, and use a container to catch fuel coming out of the line. Common cense!!!!
You can also remove fuel cap and blow into the line at Filter.
Great video. Is noone else wondering where they can get some of those needle nose for hoses? LOL
Thank you Sir. My issue was a gas cap not venting, so thank you for mentioning that!
How do you know if the gas cap isn't venting
@@StephenNorman-p8y when you unscrew the cap air either blows out or sucks in. Makes a psst sound.
Thank you for your help
Happy to help
Very well explained. Thank you for sharing.
got a yamaha virago 250 motorcycle but looks like it has the same type of fuel system. will try your method. Cheers
Can i ask why you didn't just unhook the line coming out the pump instead of the end that goes in the carb??
Sweet looking fuel line needle nose pliers. Where are they from? Nice video.
My john deere l100 is not getting any fuel from the tank to the pump. I can blow compressed air threw the line. I believe the fuel is not be sucked from the tank. The fuel pickup in the tank is high on the tank and therefore the fuel must be sucked up (no gravity feed) How can I check that the vacuum at the fuel [pump is adequate?
Great video! Thanks for doing this video!
I wish I had seen that video earlier I would had save 130$ worth of fuel filter and fuel pump. I washed the tank but I forgot to check the shut-off valve and there was the clog. Grass, obviously. Kohler Command 20hp on a Walker Mower MT-GHS.
Very good video and explanation..
Thanks for the video. I have a question the pump on my riding mower works fine I’m getting gas to the carburetor it turns but won’t start you think is the carburetor?
Useful video - thank you. But I have a vee-twin Kohler with a pulse pump and it's filling the sump up with petrol, preventing the engine from starting. Does this mean that the valves in the pump are not working correctly and it is drawing the petrol straight into the engine ? In which case I need a new pump ?
Thank you for the great video. Last season I bought a new Ariens zero turn mower from Lowe's. It ran well at first. I fueled it up today and cut for about 3-4 minutes then it cut off and will not start. It only has 4.2 hours on it. Please advise. I took the fuel line off going to the fuel pump, held it down towards the ground and no fuel is coming out. I didn't go any further than that because it's a new unit. The 4.2 hours came from 2. something from last season and less than 2hr this season. Please advise.
Good video. This is a new one for me. Engines I've had before ran straight from the tank to the float bowl. Are these gadgets actual pumps, or are they just a vacuum fuel cutoff switch? I'm wondering because I have a Honda GC160 with a crankcase full of gas. Obviously the float needle failed to do it's job, but I'm wondering if this little gadget wasn't supposed to be cutting off the fuel before it even got to the carb. Anyone know?
oh thank you so for this video, it helped me so much and yes, I did the work/checks myself.... now to get a new vacuum pump.
Hi there. I followed these and all looks good. Riding mower still surges. If move gas throttle to mid or above runs more "stable". Drop below mid and starts to surge. Any thoughts are appreciated.
Thanks for the info, it seems Polaris is guarding this test method so only the shops can perform it.
Very informative and helpful.
Thank you much
Thanks!
THANK YOU FOR YOUR HELP
Can you get fuel into the crankcase from the fuel pump? I put a brand new carb on and still getting fuel into the crankcase.
Is there a way to check pulse from engine like put your finger on it to feel for suction...my does not pump fuel but everthing is good.
my mower cranks long than it will start if i use starting fluid it starts right up does this sound like pump is bad all the ma in ntenace stiff has been done to it
does a vacuum fuel valve can force pressure to give more fuel to the carburetor when wide open throttle?
great videos! my question i have a toro SS5000 and i can only run it for about five minutes and then it will start surging and the it dies any ideas thank you
hi I have a toro cutter with the same fuel pump and was leaking out the weep holes, so I thought must be the diaphragm gone bad, replaced the fuel pump and leakes from same place ! what could cause this, mower runs fine just has this leak, cheers :-)
I am going to try your tips right now thanks so much excellent video and tips. I have a John Deere D100 lawn tractor I hope it will be the same steps. I will let you know if this did the trick.
I did all of your steps and I got my john deere running. Thanks again for the video. It saved me a lot of money....
After replacing my fuel pump, I had white smoke while running and backfiring when turning the mower off. I only ran it for about 10 minutes before the engine died and wouldn't start at all. I found the carburetor full of oil and the head gasket was blown. Cleaned and replaced both but it still wouldn't start. From your video, I see that I had my vac and fuel input lines reversed, so I was sucking oil from the crank. Anyway, thank you for showing me my own stupidity.
Very good ! But the fuel pump is mounted wrong ! The pump must be mounted horizontal with the little valve with the screen in the bottom, to let condensation and possible oil out of the pump membrane . Everyone can read it in the instructions of the pump .
It’s anyhow strange that they use a diaphragm pump on a 4 stroke engine , there is not much pumping activity do to the crankcase breather !