I have the JP21 that was modded by RW Mods in Minnesota and it is OMG fast and allot of bottom. I have allot less money invested in it than much "better" engines and it out performs them. And easy to tune. Ran it all last season, had it rebuilt by Rex at RW (piston, sleeve, rod, bearings, and go thru the carb) and it's even better. And even this idiot (me) can tune it!