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How are you checking compression? The compression release will keep the exhaust open as you spin the motor over by hand so I'm not confident that is a productive way to check compression. There are a number if issues that prevent compression from building in a motor. Bent valves, worn seat or valve face, broken or worn rings, hole in the piston, hole in cylinder, blown head gasket. Good luck.
06 Raptor SE, Barker Duals, CP 12:1 piston, Hotcam stage 3, (Kenny)+2mm TB, PC3, Dyna Prog Ign (DL700) Tuned, All new P&P Head KW springs (velociraptor),Pro Design intake, Black widow shock, Houser +2 arms +1 stem, Gibson stabilizer, RATH swaybar. American racers on douglas black labels.GT thunder TT rear shock and link. 07 SE wifes bike everything besides motor work.
2007 Raptor 700R SE orange/black, CT Racing full exhaust, HMF Optimizer, K&N air filter with Outerwear in aluminum airbox, GYTR nerf bars and full skid plates, DG bumper, Protaper bars, ODI Rouge grips, ASV levers, Powermadd handguards, Pro Armour kill switch, ITP Baja rims, Race Rex tires, lowered with YFZ front shock springs and flipped rear ...
2001 Raptor 660 stock bore rebuilt w/stock tranny ; ) - Rebuilt head - Pro X piston - Full Yoshimura RS3 - K&N filter - L&A One way bearing kit - Pro Taper SE bars - ITP pro9 rims all the way around - Renthal sprockets (12-40) - All bearings and bushings replaced by pivot works - Full skids