ORIGINAL: mihelone
Dear John,
thanks a lot for your reply.
I use a bcm wrap around pitts muffler. the engine has burned about 70-80 liters of gasoline mixed with 40:1 full synth oil, so it is fully run in. I think its a matter of prop size as I suppose from your writings...
Have you cut the crimped tips off your Bisson? That's supposed to add a chunk of RPM due to less restriction.
Have you verified your ignition timing?
Have you reset your needles as the engine broke in?
Where I live it's 4500' ASL and we have to run smaller props to get decent RPM out of the engines but even here, my 50NG with a 22x8 Mejzlik will spin at 7200 RPM measured with a TNC tach.