07-15-2010, 03:11 PM
Sounds like the vacuum port is ported vacuum. It will not have any vacuum at idle, but as the RPMs increase and the throttle plate opens the vacuum will be applied. If your getting too rich of an idle you may try using manifold vacuum. That will give you more advance at idle to help burn the extra fuel. But still set your base time with the advance disconnected.
As for the backfire, I don't believe the idle circuit would be causing your problem. The intermediate/cruise circuit sounds a bit fat. Have you tried changing the primary jets? You can get this mixture close with the jets, then fine tune with the power valve.
The backfire will also be aggravated by any type of exhaust leak. Fuel and burned exhaust won't burn. But let a little fresh air seep in and pow!
As for the backfire, I don't believe the idle circuit would be causing your problem. The intermediate/cruise circuit sounds a bit fat. Have you tried changing the primary jets? You can get this mixture close with the jets, then fine tune with the power valve.
The backfire will also be aggravated by any type of exhaust leak. Fuel and burned exhaust won't burn. But let a little fresh air seep in and pow!
'72 TBA...