A friend has asked me to try and solve problem with his k301 on a cub cadet 129. (71-74 vintage). He said it lost power and at full throttle it would stop with a backfire.
What I found is that it starts right up and runs fine at full throttle for a few minutes until a surging starts and then it just stops and flames out the muffler as it stops. It will restart immediately and again run for a short period.
This is what I have done so far:
Remove fuel cap (I admit that was not the first thing that I did)
I removed air filter.
I checked for fuel flow out of filter. It is gravity fed and flow was good.
I put inline spark tester and spark remains on shutdown. I even turned key off and then spark goes away but turning key back on before it stops rotating brings spark back and it runs with spark until the problem shutdown.
After shutdown I loosened bowl nut and fuel came out.
I adjusted both mixture screws to initial setting 2 1/2 on the idle and 2 on the high.
Not liking look of his gas I drained all his fuel.
I put 400 ml of ethanol free gas and 200ml of seafoam in the tank.
At this point I thought I had it fixed because it ran for over 5 minutes (I think as I broke my watch band so no watch) but then it stopped.
I then went and worked on something else. Just before coming in for the night I started it again. It ran for 15+ minutes without stopping. I actually shut it off to come in the house.
My thought is either a sticking float (but is that consistent with immediate restart and fuel from loosened bowl nut?) or some debris that moves to block the main jet but immediately moves away when it shuts down? Not sure why I got the 15+ minute run after some seafoam exposure.
I guess I will see what I get tomorrow when I start it.