ORIGINAL: mglavin
Rob,
Using the TACH to back off the high speed needle until you note a loss of at least 300rpm. The 1/4 turn is simply a suggestion. And remember when tuning; the low and high speed needle interact to some degree with this carb.
Running the lil beast lean will cause and affect a cough as you noted, throwing the prop/spinner and even taking out the prop hub key....
Michael Glavin
Backing the High needle off 1/4 turn is exactly what the instruction manual directs after running at full throttle for 5 seconds. That is if you hear the RPM drop...which I did here and dropped it 1/4 turn. That coincidently equated to a 400 RPM drop from 7100 down to 6700. The next cycle from idle to max (with 10 second stabilization allowance) resulted in the prop and spinner liberating before I could count to 5 and listen for any RPM drop.
The problem wasn't a large pop as much as a sudden RPM dip. The spinner and prop just don't work as built. Amazingly, I didn't have another issue once I deleted the spinner and went with only the original Syssa washer and nut.
This engine and prop set up should not be SO fragile that it can't handle the "recommended" set up procedures. Again, no problems one the spinner was removed.
I'll run her again this weekend..