518-H runs then stalls

[HerbS 6]

My 518-H runs and mows for about 15 minutes then stalls.  It'll rest for 10, then run for 15 and stall.  The oil level is right, air cleaner is clear and it has new spark plugs.  Sounds like overheating, but it isn't really very hot to the touch.  Onan twin.  I brought it to the CT Onan dealer and he couldn't fix it, but frankly, they work on generators all day and I don't think they wanted to bother.  Any ideas?  

[953 nut 55,744]

If the vent on your fuel cap is plugged the fuel being removed from the tank will create a slight vacuum the fuel pump can't overcome. Try running it with the cap backed off a little.

[HerbS 6]

Thanks.  I tried running without the cap and it still stalled.  

[The Gman 476]

Is that model ignition coil or solid state.

[lynnmor 7,352]

My guess is that the ignition trigger behind the flywheel is breaking down from heat.  If you could quickly check the spark, using a spare plug connected to a spark plug wire and grounded on the engine, might help you diagnose the problem.  The Onan manual can be found on this website and it will help you check the coil.

[N3PUY 1,031]

Stuff in the fuel tank getting sucked into the outlet screen and plugging it.  ?????? 😧 

[Tankman 3,518]

Had a similar problem with my 20 hp Onan.

Cleaned the carb, new fuel filter, air filter along with new foam pre-cleaner, oil change w/ oil filter, adding Seafoam to the fuel. 

 

Now when I park the '90 520-8, done for the day, I vac the screen and ( and ) spray some carb cleaner directly into the carb.

Seems (  ) to be running better every day. Like new.

 

For awhile I was disgusted and giving up.