[charles bledsoe]

I am posting this here in hopes that someone runs the AFB on their vehicle and has experienced the same issue I am having. I have a 66 GTO with a B body 66 389 in it, it might be from a Catalina but I'm not sure. It was a 2bbl setup that I swapped over to a 66 4bbl intake and a Carter AFB carb. I'm having an issue with a hesitation when I apply full throttle and I hit 50-55 MPH from a stand still and at 65-70 MPH when I punch it at around 40 MPH. I don't have a tach so I have to use a speed instead of a RPM to see when the hesitation kicks in. When I hit the hesitation it's like hitting a governor speed limit, but if I back off slightly it picks back up in acceleration. If i drive it normally with out stomping on the throttle she runs just fine. I have replaced the fuel pump and the vacuum advance canister, as the canister was bad. I am now wondering if I need to adjust the setting on the accelerator pump lever linkage, or maybe look at changing out the springs on the metering rods? I bought my AFB from carburetors and more about a year ago completely refurbished. It was supposedly for a 66 Pontiac. As I understand things my problem sounds more like a carb issue than a vacuum or distributor one. I did some diagnostic test and here is what I found out.

At the vacuum advance source off the tree on the back of the carb (I do have two other sources on the tree, the break booster, and the transmission modulator.) I am pulling 16.5 Hg Vac on the port going to the canister.

I am showing about 7-8 degrees BTDC on the timing placard (granted I only have 3 marks, center is 0 degrees which is TDC, and when facing the engine the left most mark is 6 degrees BTDC. The right most mark is 4 degrees ATDC, so I am guessing on the 7-8 degrees) when the knob on the timing light is set to 0 degrees and advance canister is
disconnected and the line is plugged. The book calls for 6 degrees BTDC.

When lining up the mark on the balancer to the 0 degree timing mark on timing placard by moving the knob on the timing gun, I am showing 12 degrees on the knob.

I'm showing on the timing gun knob indicator that I have 27.5 degrees total timing.

With the vacuum advance canister disconnected and the line plugged I am showing 725-750 RPM and the dwell is at 29.5. With the canister plugged back up I am showing 850 RPM at idle.

At 2000 RPM I am getting 33.5 degrees of advance. I cannot test for more than 2000 RPM as my testing unit only goes to 2000 RPM. I will look up in the book for what it calls these parameters to be at, but I think off the top of my head they are close.

Sorry for the long drawn out post, but I was hoping to give a picture of what I have and what I have done. Most of the folks over in the 66-67 side use different carbs and distributors than stock. Any help is very much appreciated.
Thanks.