Kubota 1860TG, Gas Kawasaki 18hp engine

Mower cranks fast, runs well when cold. Runs for about 20 minutes +/- depending on how warm the weather is and then chokes and dies. Will immediately re-crank and run for a few seconds and dies. Sometimes will run just enough on full choke to get it back to the garage.

I know it is a gas problem. Once engine dies I have immediately opened carb bowl and just a very little gas dribbles out.

Here is what I have done trying to correct this:

When problem is happening I have pulled gas line off carb and cranked engine and gas is squirting out from fuel pump so gas line is clear from tank all the way to the carb. Still installed new filter, cleaned tank and replaced gas lines from filter to pump to carb.

Gas shut off solenoid on carb bowl operates. Have removed carb bowl and visually inspected solenoid opening when grounding bowl against engine. Still replaced electrical connection and wire from harness to the solenoid.

Torn carb apart, confirmed float operation by blowing into gas inlet with float in up and down position. Float in good shape, moves freely. Removed all jets, throughly cleaned and blown out with compessed air. The only two gaskets on the carb are for the bowl which is in good shape and an O-ring on bolt that enters through bottom of bowl that connects to jets that lead up to the throttle body.

Edit: Tried running with gas cap off, vent is clear.

Again I know its gas and not electrical based on the bowl being empty when problem manifests. Once it sit for about five minutes, just enough gas gets into the carb to run briefly until empty again. Will only run fine after it has completely cooled.

This one is making me a little mental. Any suggestions would be greatly appreciated!

 

First think I would try is loosening the gas cap and see if the problem goes away. If the vent in the cap fails the engine will draw a vacuum in the tank until it's can't draw fuel and the engine dies. Usually letting it sit a while lets air leak back into the tank and the engine will again run. If that's it all you need is a new gas cap.

 

Sorry. Forgot to mention it won't operate with gas cap on or off and I have made sure vent on cap is clear.

 

It would be in the fuel pump. Is that one mechanically driven with an arm from a cam lobe or is it pulse driven from the crankcase?

 

Mechanically driven. Note I mentioned that gas was spurting from fuel pump with line removed.

 

And they can do that with no resistance, but the question is whether it can pump the necessary pressure (about 3 lbs) when it's running and the fuel pump heats up. It may very well have a weak diaphragm or faulty checking inside the pump. This is assuming the problem is heat related.

When you have a stopping of the engine take off the bowl and see if the pump will pump fuel past the float valve with the float partially raised.

 

Makes sense to me. I'll give that a go and thanks for the reply.

 

Make sure there is nothing stuck in the little port that seals off with the float needle. I have had once or twice something that got stuck in the carburetor in that area, creating a blockage right there at the inlet. Also, if the carb has a rubber seat, it could be swollen and restricting fuel flow (seen that many many times).