Spark is firing too early T F I o I at the O

[stuartshomepc]

I picked up a GY6 powered atv put in new rings, honed it, lapped the valves and triple checked that the cam is in correctly. It has 135psi cold compression and the valves are both at 0.004". However when it tries to run the spark fires way early, right as the magnet passes the tripper pick up.

There is a T F and the I O I on the flywheel, with the O being a white dot of paint, about3/4" forward of the F. And that's where it's firing. I replaced the CDI thinking that was it but the new one (5wire A/C) acts as the old one did.

Any thoughts on what this could be?

[xlint89]

Make sure the piston is at the very top of the bore while the 2 small holes on the cam are aligned with the head. (big hole at top of cam)

[stuartshomepc]

Yes, when the head was off I verified that the TDC mark on the flywheel was TDC on the piston (elimate a sheared keyway). And am certain that the cam is in correctly. The compression is good but the spark seems to be firing right as the magnet on the flywheel passes the trigger pick up coil. Which is about 30 degrees too early. Iv'e wired in a new A/C CDI and even a new DC CDI and the problem is the same. If you look at the flywheel you see the T. F. I. I. (Two lines way advanced of the F mark). There is a dot of white paint in between the two I. I. Marks and that's where it's firing.

[stuartshomepc]

The spark is firing way ahead of the F mark (at the white dot) like shown in this video captured with a 0 degree offset timing light GY6_spark_timing.wmv
and this picture