We did a ton to my sons CRF150R, including gearing, flywheel, etc... The video is long but covers almost all the mods. I think the best where gearing, G2 throttle tube, Power Valve (similar to FMF Snap), radiator guards, and flywheel weight. After riding it a season, the bike performed great. My son had trouble starting it once (cold), and it took forever to clear the flooding, etc... But it normally starts well hot and cold, has nice low RPM throttle response, and has been a great bike. We spent way too much money on it, but it was a fun project and learned a fair bit.