ORIGINAL: ArcticCatRider
A colder plug will help pull heat away from the combustion chamber. Excessive heat, load, and pressure are what cause motors (any) to knock.
No matter how tight you go on the prop nut, and/or jam nut....it's not enough to stop a prop from being at least loosed...and likely thrown. It is not cool when this happens....so make sure you and your buds are behind the plane the whole time until you get the needle figured out! I've had them fling near 20 yards away before...lotta energy.
It might not be a bad idea to grab a tach...get to peak, then back off a few hundred RPMs. Remember to make small adjustments, and wait a few seconds in between adjustments...let the motor respond
I remember on my old FS91 was when I had taken out the glow plug and later just put it back in finger tight. A long time Later I used the engine on an airplane. and on its maiden flight take off flight the glow plug came loose and that sucker threw the prop and spinner. I was lucky and made a landing Ok, but it was exciting though. I found the prop and spinner, but the two nuts had disappeared. so i had to get new ones of course. I tightened the glow plug down like it was supposed to have been done, and the engine worked fine from then on.
I remember using a FS40 engine back around 1990 in a airplane and I only ran 5% nitro fuel. It ran just fine for me. I never tried running a higher nitro content fuel at the time I owned the engine.