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Old 12-05-2011, 11:52 PM
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DoubleVision DoubleVision is offline
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The problem is obvious. You can`t run stock valve springs on a big cam. The springs must match the cam. Why is because right off idle, the aggressive lobes of the high performance cam causes the springs that are too weak to create valve bounce. Through the RPM band power is way down from where it should be due to this. You said you didn`t have flat top pistons, which do you have? Dish top? Dome top? If the pistons are dished and with stock heads your compression ratio with a stock replacement head gasket is around
7.9:1. That cam has to have at least 9.5:1. You can`t stick a big cam in a stock engine and expect it to work correctly. The high RPM stutter can be caused by many things, but I`m willing to bet it`s caused by valve float as the stock springs can no longer stabilize the valves on a cam that big at upper RPMs. The easiest fix would be to swap cams to something alot smaller, a edelbrock performer plus cam would work and it would live with stock valve springs. But every cam should use it`s matching springs.
Lastly the rich idle is caused by the base timing being too low. Now the carbs throttle blades are so far open to get it to idle with the big cam the butterflies are off the idle circuit slots which is causing the carb to draw from
the boosters at idle, causing what I call a "runny nose"
The timing should be 12 degrees before top dead center with vacuum advance disconnected and plugged. Afterwards, reconnect the vac advance to a full time manifold souce, this is a source that pulls vacuum full time, including at idle. Recheck timing, it should be 18 to 24 degrees before top dead center. When you connect the vac advance to a manifold souce the first thing it`s going to do is idle up, then you lower the idle speed on the carb and it places it back on the idle slots.
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