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