Running my Y 63 yesterday. Could not fly for other reasons. At max RPM I could hear a crackling noise. This indicates to me that I am having <u>predetonation occurring</u>. Engine accelerates well, rapidly. Idles good. Using OS Type F glow plug and Byrons 20/20 fuel. Can anyone confirm detonation and what's the cure? I already replace the diaphragm in the regulator. Original diaphragm would not let me get over ~8,400 RPM and detonation wouldshut the engine down.

I had to replace the gasket between the rear crankcase and the carb set up, it was leaking oil.While in there noted that all was okay, nice and oily indicating good lubrication going on.

Advice please.

Chip

Unlikely pre-detonation unless you are running 50% nitro. YS are relatively low compression engines.
Have you set the valve clearance lately? Did you replace the plunger with the diaphragm? It's also possible you are a bit lean.
What prop are you running and is it tight? I chased an engine problem all day once that turned out to be a slightly loose prop.

Another possibility is the rotary valve, did it get located back correctly when you had the carb off?
The rotary valve must go on properly located on the crank pin.

Thanks.  The rotary valve is keyed, it goes only one way.  There is a slot in the back of the valve and it fits on the crankpin extensiton.  Don't think it can be put on wrong.  Engine runs well, it just makes the "cracking" noise.  Yes, I have move the HSN about, the noise does seem to be reduced on the rich side.  Later read through the instructions and noted the direction to richen up the engine an 1/8 of a turn after getting it set up right.  So I suspect the engine is a little on the lean side, but it accelerates very very good. 

Turning a 12 X 8 Master Air Screw K series prop. 

Weather permitting will take it out again.  A very powerful engine.

Chip

Bearings.