hulio516, try some fresh 5% wildcat in it, you may have a higher compression OS that may run better on 5% fuel, The Fox engines in the 80s used to crackel if higher nitro was used in them as they were designed for low or no nitro fuel. Too high nitro will boost your advance timing and as a result the piston could actually fire multiple times btdc (before top dead center) during a single combustion stroke (that is why you hear crackling) because it is running overheated regardless of needle setting , I had a rossi 60 that hated 10% fuel and it sure let me know it very rudly, It would overheat even if I flew it rich and it would blow a glowplug after every flight, some do and some don't , this one did so I went back to 5% and it cured my problem.. It could also be your fuel-glowplug combination also..You could need to go back to running your OS with the stuff that worked in the first place and it could be that 10% of the same brand needs to be used as before, It could be that you have a finiky or picky engine, let me know what transpires , Best wishes greengoose....