I recently stripped and re-built the top end from my 1990 TRX 300 Big Red. I replaced piston rings, head gasket, valve stem seals, lapped in valves etc etc. I timed the engine in conjunction with the Haynes manual. When I restarted the engine after re-build it was missing badly and very lumpy on low throttle/idle but seemed to pick up and rev fine on full throttle. I re-checked the timing and noticed the lines on the cam sprocket don't line up exactly with the cylinder head face - possibly half a tooth out or less. After several attempts of adjusting the timing I still can't get them to line up exactly.
Is it known for the cam chains to stretch on these engines? The engine was running perfect before I stripped it and I can't see how the chain could have stretched? I have since removed the carb and currently in the process of overhauling that just incase it's a fuelling issue. If that doesn't cure it then I'm stuck? The valve clearances are spot on, plug gap fine - basically all the routine checks are good! The only issue I have is the cam sprocket lines not lining up exactly straight when the crank is at 'T' mark.
Any suggestions would be very much appreciated!