[Synchro909]

I'd be looking at the electrical side of things. A dodgey aftermarket ignition switch is a common cause of trouble, as is the coil and especially the condenser. While your timing is right, you say, I'd also check for the infamous #3/4 crossfire and other places where spark might be tracking to places it shouldn't.
Having said all that, remember that half of electrical problems are in the carburettor!