ORIGINAL: s�rpet
My newest fox engine .25 is not good engine it vibrating very badly high revs, leak fuel from front bearing, cant hold needle settings, itry many different fuels, synt, castor, low nitro, no nitro, high nitro.
Os .25fx is 100% better engine.
This is exactly how iron piston engines behave when not broken in. Takes a loooong time to break in. Probably over an hour of run time or 4 to 5 tanks of fuel. The vibration is the natural vibration of a heaver iron piston, plus the friction of a tight piston liner fit. It won't hold needle settings till broken in. Not sure about leaking from the front bearing, all engines leak some or at times, but possibly some back pressure. I think it could be a poor fit between crank and case, but others can better help you with that as I do not know what clearance it should have.