OS FS-120S-E
 

Having problems with this engine. It 'acts' like it leans out when the engine warms up, but is still running rich. Tightened all the engine screws and nothing seemed to be particularly loose. Found the valves needed adjusted, especially the exhaust valve. The valve gap for both intake and exhaust were over the recommended gap. Adjusted the valves to withing specs but was wondering if there was anything else to check.

Thanks

RE: OS FS-120S-E
 

What propeller are you running, and at what RPM? You want the engine to turn in the 9,000's when leaned to just rich of peak RPM at full lthrottle. You need a tachometer to get four-stroke engines properly-tuned. If the engine is turning much slower than that, you have too much propeller, and the engine is being overloaded. We've even propped them for near 10,000 RPM and they'll run "all day" like that.

RE: OS FS-120S-E
 

I am using and APC 15x8. I have a tac. and tune all my 4 strokes with it. I will check the rpms and adjust the prop as necessary.
Thanks for the help.