YZ timing the exhaust cam therefore makes the cam timing safer!!!! Taffy - Maybe you can explain to us poor poor slow witted sods how having the valve open farther at TDC with YZF timing is safer? Here on planet earth any delay in exhaust valve closing, like retarding the cam timing 20+ crank degrees with YZF cam timing reduces the exhaust piston to valve clearance. Miraculous as it might seem we do agree on one thing, the YZF timing is perfectly safe and wasn't the root cause here. Do carry on and please enlighten us ohh Duke of Piffle. I'll make sure and take notes.