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intermittent max rpm problem


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My HE R120 has an intermittent problem. Sometimes with full throttle, it reaches max rpm (about 9400rpm) but then rpm decreases to about 5000rpm. When i release throttle and immediatly go back to full throttle, I get max rpm.

I recently changed spark plug, fuel filter, fuel lines, carb gaskets, did a carb rebuild and I use fresh fuel (2,5% ratio). Reed valves are ok. 

Does anyone have an idea what the problem can be?



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  • 4 weeks later...
  • 1 month later...


Problem wasn't solved after replacing the piston rings. Finally I did a leak test and found that there was a leak in the crankcase. I first made a new paper gasket but that didn't solve the problem. Then used Loctite 5980 to seal the crankcase. Did some flights, engine is running well, max RPM is 9600, Max CHT about 175°C.


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