[steve25]

One quick way to check jetting is this.

Get the motor fully warmed up.

Disconnect the carbs accelerator pump.

With the motor out of gear and idling wing the carb wide open.
There should be no backfire which would indicate a lean condition.

If you hear no backfire which then you at least in the start of ball park in terms of wide open jetting needs.

[Kenth]

Originally Posted by steve25

One quick way to check jetting is this.

Get the motor fully warmed up.

Disconnect the carbs accelerator pump.

With the motor out of gear and idling wing the carb wide open.
There should be no backfire which would indicate a lean condition.

If you hear no backfire which then you at least in the start of ball park in terms of wide open jetting needs.

No one in their right mind should use your method.
It says NOTHING about how accurate the calibration is.
If it would work without an accelerator pump why do ALL carburetors have one?

Instead use the "tip-in" test with the choke blade or the palm of your hand at about 2200 rpm.
A small increase in rpm of about 50 rpm indicates a proper mixture.
If the test run turns out to be satisfactory then all is well.

FWIW

[Skidmark]

Originally Posted by Kenth

No one in their right mind should use your method.
It says NOTHING about how accurate the calibration is.
If it would work without an accelerator pump why do ALL carburetors have one?

Instead use the "tip-in" test with the choke blade or the palm of your hand at about 2200 rpm.
A small increase in rpm of about 50 rpm indicates a proper mixture.
If the test run turns out to be satisfactory then all is well.

FWIW

I don't understand how attacking a fellow Pontiac guy is helping the hobby. I mean how is helpful saying "no one in their right mind" so I guess calling Steve crazy is good for the hobby.
I went back and read all your reponses for the last few months and I see a pattern.

I don't know Steve, but he sure offers a lot of help here to fellow Pontiac fans and I for one appreciate it. No place for bullies here.

FWIW

[chiphead]

Do you have pin gauges and the tiny carbide drill bits? I'd pin gauge those accel discharge holes and go up 5-10% on the area of the holes. Depending on diameter, about .002"-.003" larger should be a good starting point.

If you can figure out where the IFRs are, you can go up a scootch on those too. If the transfer slot is lean, then richening the IFRs will add fuel.

[Formulajones]

Usually when you have a brief stumble or lean spot off idle before the main circuit takes over as you described, it either the pump circuit or the power valve circuit.

If you increased main jet and it helped it's likely covering up the issue you can accomplish the same with the idle circuit as well by richening that. Typically not the best approach but some engines also don't like lean mains or lean idle circuits either. It's a game of back and forth.

If youve messed with the pump circuit with no improvement then the other likely cause could just be too much of a delay in the power valve circuit. It has to work in conjunction with the pump shot. The pump shot alone won't always cover the lean spot when the throttle cracks open. That momentarily drop in vacuum should also trigger the power valve circuit if for only a second.
You may just need to change the power piston spring.