Ok guys needs some help here ready to set this thing on fire..thing would never start valves were tight i adjusted the calves to correct shims on intake n exhaust have plenty of clearance in between cam lobes n shims..problem is i done set tdc about 10 times now its dead on..will not fire one hiccup sprayed gas into carb while cranking n while not all it does is make a loud backfire n some flames come out. Its like valves are tight but there not.idk how it could be firing wrong with it at tdc. I need help asap carn is clean have plenty of spark bright blue.