Robin 35 losing power after gets hot.

[cncsmyhobby]

I have about 10 hours on my GEBE with a Robin 35 engine. I need help diagnosing a power loss problem. After about 3-4 miles of pretty hard riding with stops and starts around my residential neighborhood, it loses top end power as if starving for fuel. I have tried different fuels, run it with and without the air filter, disassembled and cleaned out the carburetor, and fuel line filter, replaced the fuel lines. The spark plug looks very clean. I am thinking that I need to check the valve clearance. Any one else have this problem and want to share?
Cheers, Bill

 

[darwin]

Try riding it with just half a tank of fuel, assuming your using OEM tank. Just tighten the fuel cap half way and see if issue goes away, if it does your cap is not venting properly. Half tank is suggested to avoid spillage.

 

[cncsmyhobby]

Thanks darwin, that was it! The little rubber check valve in the cap was stuck shut and would not allow air into the tank. Makes perfect sense in hindsight.

 

[Sidewinder Jerry]

Often it a simple fix; be glad when it is.

 

[darwin]

Yea with a new soobie I didn't think it was a carb problem.

 

[Sidewinder Jerry]

I went and stuck a pin through my vent holes just to make sure they were clear.