Originally Posted by
w8ye
I would check the cam timing. My experience with the Magnum/ASP four strokes is that the cam is often set wrong.
With the cam mark straight up or down, the engine will idle down - (tick like a clock), start easy, etc but not turn 9600 rpm with a 14 X 6.
With the cam mark correctly aligned with the push rods, the enginer will be lucky to idle below 2500 but will turn a 14 X 6 @ 9600.
One way to double check your cam timing is to check the valve overlap position. Find top dead center on the compression stroke. Then turn the prop one full turn. One valve should be just opening and the other valve almost closed. The exact center of the valve overlap event (rocker arms parallel) should be around 5 degrees before top dead center. If one valve is closed at top dead center on the overlap stroke your cam is set wrong!
It looks like the overlap where both rocker arms are even happens at 5 degrees after TDC. On the compression stroke they are both closed, I turn prop and intake opens, exhaust opens, both are open at 5 BTDC but at 5 degrees after TDC the rocker arms are parallel. When both valves are closed there is quite a bit of play in the push rods.