The manual of Four star said that four stroke 70 size engines would be thw most suitable engines for this plane.
So, I put on os 70 on it when I also had os 91.
It barely flew and I couldn't get much out of it.
Even accepting it as a basic low wing trainer, it was very underpowered.
When I read the forums here and compare the suggested engines and the ones people really use, ther is a big difference.
Some people even use 90 size engines for 40 size airplanes.
Is there any guide lines to follow for the right size engines?