RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
Wow... Cool!
I assume you've got a two ring piston, yes?
I've had trouble getting a steady reading on my tach. It normally jumps around plus or minus 40 rpm. I'm not sure how much of this is instability of the motor itself or whether the tach is not getting every pulse of the prop blade. When I test it on a 60 cycle electric light bulb it's dead on. The APC prop is gray, a pretty neutral color, so maybe the sensor has a hard time picking it up against the background. Maybe if I took a black marker and colored it up it would help. I'll have to try that! The tach I've got is a "GloBee" from Tower Hobbies but I'd bet all the R/C marketed tachs are basically the same.
diceco