Export thread

Hello,

I have a kohler command single in the shop. I think around 17-18 HP. (model # is worn off) It has a mechanical fuel pump mounted to the side of the block, and has a problem with leaking gas into the cylinder. Weve tried two different carburetors. Rebuilt with new needle valve and checked the float for problems. Everything seems fine, and sometimes won't start leaking until a day or 2 after reinstalling carb.

Could the fuel pump be causing excessive pressure against needle valve causing this leak? Or is it just something wrong with the float valve?

Fuel pump without running won't create pressure to override the float valve. Leaking fuel pump would leak into the crankcase not the cylinder. I suspect it is a carb issue, but two different carbs should eliminate a float valve issue. Could there being something blocking the bowl vent like a gasket not installed correctly. Seams like those older command singles vent from the rear of the carb through the gasket between the carb and that plastic isolator. If the vent is plugged will cause a siphoning effect.

Many of the Walbro carburetors on both the Command and Courage engines has float valve inlet seat that can leak after they wear and Kohler does have replacement seat kits available. You would to determine if your engine has a single barrel Walbro and if so them you need install the pressure seat version of the kits. These kits are available in both gravity and pressure so would need to install the correct provide you have the Walbro carburetor.

cbs123 said:

Hello,

I have a kohler command single in the shop. I think around 17-18 HP. (model # is worn off) It has a mechanical fuel pump mounted to the side of the block, and has a problem with leaking gas into the cylinder. Weve tried two different carburetors. Rebuilt with new needle valve and checked the float for problems. Everything seems fine, and sometimes won't start leaking until a day or 2 after reinstalling carb.

Could the fuel pump be causing excessive pressure against needle valve causing this leak? Or is it just something wrong with the float valve?

Click to expand...

Just to make sure it's not a bad carb, I have a place where I can hand carbs level, with a fuel tank mounted to goes to the carb. I won't take long to make sure that's the problem or not. But I'm with @ILENGINE, the chances of it being a needle problem is unlikely. Especially with the original then two replacements doing the same thing.
A good vented fuel cap or a vent line that's not clogged shouldn't allow any pressure in the fuel pump.

After reading this thread I’m very confused about what is going on. First, raw fuel entering the cylinder but not the crankcase? Second, two different carbs, plus rebuilding carb and problem not solved? Kohler single cylinder Command engines use a mechanical fuel pump, so fuel running from the tank, through the carb, into the cylinder when the engine is not running would mean that both the pump and carb need to be bad. The pump would need to have both inlet and outlet valves sticking open and the carb needle not seating, all happening at once to allow the fuel to flow when engine is not running. Very possible, but highly unlikely. Next, fuel only entering cylinder, but not crankcase? Can’t be a lot of fuel doing this, or excess fuel would be leaking into the crankcase. That being said, I have questions of the OP. First, how much fuel is entering the cylinder? Second, have you checked for fuel in the crankcase? Third, how did you clean and rebuild the carb? Fourth, when you switched carbs, how did you know what carb to use without numbers? You do know that pump and gravity carbs are not interchangeable? Fifth, how much fuel is actually leaking into the cylinder? Will the engine start, but just run very rich until the excess fuel is burned off. Sixth, what do you do each time it happens? Seventh, is this a vertical or horizontal engine. I know that you may feel I’m asking some stupid questions, but you must paint us a better picture of your problem, as we are only guessing because we are not standing next to you. Or you can read my signature and disregard this post as not relevant.

Hey guys, thanks so much for the advice. Very much appreciated. It turned out to be a simple problem. The tank was full of trash and there was no filter on the line. So trash was getting in the needle valve and preventing it from closing all the way. Doh! Should've known better.

Thanks for the help

cbs123 said:

Could the fuel pump be causing excessive pressure against needle valve causing this leak? Or is it just something wrong with the float valve?

Click to expand...

The fact it has a pump tells me the fuel tank is BELOW the carb, therefore your issue is not related to simple gravity.

Going by your description then, the pump must be over-active for that particular carb and float valve setup. I see 2 ways to limit the pump's output...
1) Push a screw-in main jet (or other doughnut shaped part) into the vacuum line that runs the pump. This will reduce the impulse from the crankcase, and thus reduce the volume and pressure coming from the pump.
2) Disassemble the pump and place an object (such as a hex nut) inside the diaphragm that will limit the stroke of the diaphragm. The object must be smooth so that it doesn't pierce the delicate diaphragm. By restricting the total "throw" you will restrict the pump's output.

Hope this helps.

Along with the new fuel filter, put in a new inline fuel shutoff, and use it.

It saves a lot of time, trouble and money.