Hello, I have a 69 deville convertible with a stock 472. It's got a Quadrajet but not the original one. It looks rebuilt though I do not know how long ago nor how good of a job was done during the rebuild. The performance of the car was flat across the RPM range. Checked the timing and it was advanced beyond the timing marks on the pulley but retarding it would make it work even worse. When flooring it it would simply die on me unless I let the accelerator off. In cold weather the hesitation was not as bad. I found the timing chain to be severely stretched. Just finished installing a Crane Cams roller timing chain set (OEM timing marks), new vaccum pot, new fuel pump and gas line. I switched the points to a Crane Cams electronic ignition and put in new plugs set to .035. I set the timing according to the shop manual (5 degrees BTDC). Now my acceleration is much better but if I step on the gas the hesitation is still as bad as before. It just quits on me. Once again when its cold outside the hesitation is not as bad. If I remove the vaccum advance hose from the pot the hesitation almost goes away when I floor it from a stand still. Any help would be greatly appreciated. By the way my gas mileage sucks!!!!

Well if that Crane Cams electronic ignition is HEI, then your spark plug gap should be closer to .06 I think. The original points system was much lower power and could not handle the larger gap the HEI uses. That'd be a place to start anyway.

Thanks for your reply. The ignition module I used was to simply replace the points, it is not HEI. I am still using the original distributor.

Thanks for your reply. The ignition module I used was to simply replace the points, it is not HEI. I am still using the original distributor.

Have you tried adjusting the air/fuel mixture on the carb? Seems to me that could be another likely culprit, especially since you say it works better in cold weather.

Sounds to me like your secondary air door is opening too fast.
First, check the air valve damper on the passengers front side of the carb.
With the enigne off, push the damper arm all the way in, then see how long it takes to go back out. If it just snaps back out, you needa new one.

Next, look into the spring tension on the secondary air door. Look at the bottom of the page on this link: http://www.73-87.com/7387garage/drivetrain/myqjet.htm

HTH