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.


Jimi B says:

Where can I get those fuel line pliers and what are they called ???

Elquisto Brown says:

My fule pump is leaking oil, why?

Jim Snellen says:

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.

Samuel Smith says:

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 🤔

ggg's fan says:

I have a dixiechoper mower cranks to long b4 starts but once it starts it runs fine. Any suggestions ?

Shawn Dudeman says:

do these fuel pumps need to be primed to get them to start sucking fuel?

Bobby Richardson says:

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!

Fred Hart says:

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,

Tom Vet says:

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.

Donnie Cook says:

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!

Greg D says:

I need a pair of those fuel line pliers!

Adam Bilbrey says:

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!

Reseller Rockefeller says:

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

Grant MacLaren says:

Weell done. Thanks.

george brown says:

Good video. Very helpfull.

JuicedMoose says:

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.

Randall Highsmith says:

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!!!

james nagle says:

Thanks brother.  Great class!!!


great video.. helped me out

Jeff Booher says:

what about the fuel pump pumping gas into to the crankcase

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