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Old 07-29-2013, 03:24 PM
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Originally Posted by rogus View Post
It stumbles under hard acceleration. The spring tension, should it be increased or decreased?
Increased- IF it's being caused by the air valve opening too quick. But it may be the accelerator pump giving an insufficient shot or the power piston spring too weak, or the secondary choke pulloff is too fast, not enough timing or even too much timing, etc.

Start out by setting up the ignition advance first. THEN work on tuning the carb. Info on setting the advance curve here.

if it is a timing problem would that normally be too far advanced or retarded?
Most often the initial advance is too low. But you can't just add a bunch of initial timing w/o seeing where that puts the total timing. This is covered in the link above.

One last question. I noticed when I rebuilt the engine the vacum measured at the intake manifold increased to 25 inches while at idle (about 1000 rpm). Can this be part of the problem?
This could be caused by too much initial timing, idle speed too high (and too high of an idle speed can start the mechanical advance to come in). Unless you have a radical cam, the idle speed needs to be lower.
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