hm80 stalling

[jsgagnon]

Hi

I知 having a problem with a HM80 in my MF-8 lawn tractor (from the 70? and I知 out of ideas to troubleshoot this, thought I could get some help here! It痴 starts pretty well when cold and runs ok for about 15 minutes then it stalls. Can稚 be started again, only after I let it cool down. It maybe overheating, it seems very hot when I open the hood.

Here is some of the things I have done so far, but I知 no mechanic so not sure about everything:
- Check the gaz cap vent, also tried removing it.
- Change the fuel filter
- Rebuild and clean the carburator
- Change the coil, points and condenser
- Check the valve clearance at dead center,
- Remove the head, looks like the valves are seating properly, cleaned the black stuff and put back head.
- ｸ
Any ideas what I can check next?

Thanks!

 

[ILENGINE]

Possibly a valve sticking open when the engine is hot.

 

[jsgagnon]

Thanks. I didn't removed the valves but I was able to looked under them with a flash light and the shaft look to have some black stuff on it that I cannot clean without removing the valves. I would need to get some tools to do this. I also forgot to mention that the engine backfires when I stop it (hot). And another thing, I can hear the sound of exhaust changing before it stalls, like there is more air flow.