Small Engine Repair: Checking a Vacuum Fuel Pump / Fuel System on a Kohler V-Twin Engine



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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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32 thoughts on “Small Engine Repair: Checking a Vacuum Fuel Pump / Fuel System on a Kohler V-Twin Engine

  1. Good video except you only covered two of the three connections on the fuel pump, the inlet and outlet of gas flow. What does one do if there is nothing coming from the crankcase line? The pump fails to operate because the vacuum line is not doing anything.

  2. What would it be if it will run but won’t rev up only on choke it’s a Briggs and Stratton vanguard 18 hp v twin and if it is coked it will run good and smooth 🤔

  3. 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!

  4. I was not getting any fuel flow I replaced the fuel pump, but still no flow,
    I then checked the vacuum line to the fuel pump, it had a split in the hose on the back side,
    I replaced the vacuum hose, then the new fuel pump worked, I just wasted the new fuel pump, but got my mower running again,
    So always check the condition of the vacuum line,

  5. 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 YouTube 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.

  6. What happens when you run it for a while, shut it down , try to restart and it doesn’t start back up? It sounds like it’s not even taking the fuel, it’ll start up first thing after it’s been sitting all night!

  7. 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!

  8. Do you know what would cause a Kohler 22.5hp v twin motor to surge and backfire while mowing? I have a older Craftsman Command Diehard lawn tractor that is having this issue and i cannot figure it out. Any help will be greatly appreciated. Thanks

  9. 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.

  10. And next we are going remove the seat , steering wheel the battery and the mowing deck. WHAT The hell? Just take the carb line loose from vacuum pump to check pump discharge run a short hose to a can or bowl.. why take unnecessary items apart? You must have a lot of extra time .. wow!!!

  11. 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!

  12. 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.

  13. Good video. Eassy to understand etc. … I just did all these steps & it still the same problem …. Spray carb cleaner down in it,it fires Up , then Dies as soon as the carb cleaner is burned out in like 3 seconds. Tried gas,same thing …….fires Up strong then quickly dies once the gas is burned out. Got good gas goin into inlet line all the way back to the tank. … Plugs maybe? I dropped the Bowl under the carb & it had a few black speckles in the bottom,cleaned them out,put bowl back on,primed the carb …………same thing …..Fires up & dies within a few seconds. GRRRRRRRR! My yard is like 12" high grass ,this sucketh.

  14. 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?

  15. I need help guys…I have a Cub Cadet SLT1554 with a 25-27 horse power engine. I'm not getting fuel from the fuel tank to the fuel filter. Me and my son replaced the fuel filter and fuel vacuum pump as well as the spark plugs. By the way, this mower was given to him by his landscaping boss because it was for his elderly mother. It sat up for several months. We drained the tank, which took for ever. We made sure that it doesn't have a fuel shut off valve also. When I removed the fuel line from the filter, nothing comes out even with the fuel cap off. We removed the line from the bottom of the fuel tank and there is barely any fuel dripping from the bottom of the tank. Is there anything in the tank, besides trash, that would restrict fuel flow?

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