Hey Bill, Happy New Year, have a older 52-4C hand me down, it was gumed up,pulled back plate and plug,cam cover and vc. Soaked in trans oil for a week, All loose now,cleaned it out and lightly oiled it. Comp. feels good fueled it up with Gloplugboy 24% Nitro,17% Castor,59%Meth.,flip,flip,flip and it started,very cold here,so i let it idle for a while,at half throt. there is a rude snappin noise. I'm swinging a 12x5 wood zinger. To much prop?,to much nitro?,detonation? Any thoughts?

You have too much nitro in the fuel. It will run best with about 10%-15% nitro in the fuel. The noise you are hearing is likely detonation. When the engine is set up correctly, you will want it to run in the high-9,000's at full throttle on the ground when leaned to just rich of peak RPM.

Hey Bill, Thanks alot! Been an auto tech for years, I guess thats what detonation sounds like with valves only a few mm's in diam. Thought I screwed the pooch. But like we say at work,"It ran when it got here", thanks again!

Love those old ones! 15 years or so,stuck solid.Now in my Mambo.

Some of those older engines were of very high quality and will seem to last forever when properly-run and taken care of.