I have a OS 46 FX that is making this -cang cang cang noise at 2200- 4000 rpm. Mixture changes affect little unless drastic. 15% nitro 18% oil blend OS A8 plug. would this be to hot a plug [timing to advanced] situation. possibly in combination with the high compression. This eng. only has 1/2 gal. of fuel ran though it for break-in It's going in a kadet senior. It's all bare bones ready for monocote.

It won't be pinging at idle so the noise is coming from something else. It's extremely difficult to diagnose a sound but all I can think of right now is maybe a loose baffle in the muffler or the crankshaft floating in the bearings giving a rattle like a bushed bearing engine does at idle.