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Old 06-22-2012, 10:39 PM
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cobalt327 cobalt327 is offline
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Quote:
Originally Posted by wma1950
could the acc pump cam being on backwards have messed up the acc pump or ruptured the diaphragm?
Possible, not probable. If the diaphragm is ruptured, you will have a leak from the cover and no pump shot.

The pump has to give a shot the instant the throttle is opened, and at WOT there must be at least 0.015" clearance between the pump arm and the linkage.

A couple things might be happening that is screwing the off idle response up.

First is the initial timing. That cam will no doubt have a lot of duration and overlap. This requires a LOT of initial timing.

This will mean the carb primaries will need to be open so far to get an idle that the carb is actually idling more on the transition slots than the idle circuit. By increasing the initial timing, the idle speed will increase. That allows the primary throttle blades to be closed back down, hopefully enough that the carb will be idling on the idle circuit and not on the transition circuit. If this is happening, the off idle transition will be poor.

You can check for this by seeing if the idle mixture screws change the idle or not. The engine should stall or nearly so when the screw is turned CW all the way. If the engine continues to run, you know the primary blades are open too far.

The other thing is, if the carb primaries do have to be opened real far, the accelerator pump cam should be installed in the #2 position. This will allow a full shot even w/the primary throttle shaft rotated open, because of how the #2holes position the cam.
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