Monsieur Dupuis,


The larger prop you are using is holding your engine far below its peak torque RPM...

As such, it cannot possibly come close to its performance objectives.

You must never prop any engine to below its peak-torque (you can find this 'unhealthy' range, where using a slightly 'heavier' prop will cause a greater RPM loss... because the lead is increased AND the torque is decreased).

The rated HP can only be possible, if the engine can be spun at 9,000 RPM, with a smaller than recommended prop.


You did not state what type of silencer you are using, so please see [link=http://mvvs.cz/mvvs%2026.html]this web page[/link] for bench-mark RPM numbers.

An engine spinning at a lower RPM does not give proportional HP numbers.


If you have stick-shift car and you try driving it in top-gear, at 20 mph, it will not accelerate very well...

This is what you are doing by over-propping your engine.

...And, over-heating will result despite the fan...