Cub 3235 either stalls out or loses power after 30 minutes of cutting

[Paul ski]

I have a cub 3235 and after about a half hour into mowing the engine losses power then it goes through a cycle where engine revs up then down. I changed gas, used a gas treatment, cleaned everything off engine shroud so air flows, new plug, filter, oil, air filter. cleaned anything around engine and carb. Spark test was a solid glow although i would have suspected a stronger brighter spark when compared to a push mower. Now runs longer but still same result at some point of lost power. Removing the side panels helps so i think the issue is when engine heats up. Also note it does stall out on some occasions. Thoughts? Thank you.

 

[spndncash]

Check for vacuum leaks to the fuel pump or in the intake/carb. I think your fuel pump is part of your valve cover I don't know if it is mechanical off the valve train or vacuum driven. either way make sure it is tight and in good condition also make sure your fill cap is tight and seals properly. If the pump is vacuum driven a loose oil fill cap would make it not get vacuum/pressure and therefore no fuel.

 

[jstich]

If you loosen the gas cap, does it keep running?