I use the phrase "4-stroking" loosely. You know the sound I'm referring to... when an engine is still running rich, but occasionally gets "on step" to full RPM. Kinda' like:
Bap-bap-bap-bap-bap-brrrrruuuuummmmmmm-bap-bap-bap-bap-bap--brrruuuummmmmm

Almost like a Harley Davidson sound... I assume that was the reason for the fluctuating readings.The RPM's weren't changing wildly. For 20-35 seconds it would be 9600-9700 (sounding rich), then for 10-15 seconds it would be 10200-11000 (with a proper lean sound), then back to the rich sound.

The LHS is closed Mondays, so I can't get a new prop till Tuesday. I'll tach it again then, and hopefully I can get another person with a tach to confirm things.

If I knew I could consistantly convert these with those numbers, I would buy out the surplus center's stock and make my living doing conversions... This may just be beginner's luck, but I'm wearing an ear-to-ear grin.