I just completed the rebuild on the drivetrain on my 68 Firebird Conv. It has a 400 motor with a comp. cam XE268H 268/280, edelbrock performer rpm, edelbrock 750 card. The th400 was rebuilt and I'm running a TCI 2000 stall converter. If I take a trip or ride in it, and go to start and drive it afterwards, when I but it in gear it quits running. I restart it and it repeats the stalling. Only after I have to "power brake" it can I get it in gear to it drives fine. What is my problem? Has this happened to any of my fellow Bird lovers? If so what did you do to fix the problem?
Once you get the car in gear, do you still have to "two-foot" it?
I had very similar symptoms, with the engine also lungeing from about 400 rpm to 1200 rpm every couple of seconds when in gear. I solved it by changing my mechanical advance curve to have it start at about 1200 rpm, have a total of 22 degrees in by 2500 rpm, and set the initial timing to about 12-14 degrees. The vacuum advance was hooked up to ported vacuum, not manifold vacuum.
My problem appeared when I put in the 041 cam (231/240 degrees @ .050"). Yours has enough duration and overlap to be the culprit. If you haven't set up your distributor similar to this, that would be the first place to start IMHO.
Thanks for the replies. The choke is wired so that it would not interfere with the carb. After it get hot I have to "two foot" it to get it in gear and keep it from stalling. I appreciate the info on your experience and will have to look into the dist. By chance can you give me some idea on how to perform the changing of the advance to move up the rpm.
Heavier springs on the mechanical advance will raise the starting point of the curve. To help isolate the problem, you can temporarily wire the advance mechanism to keep it from moving, unplug the vacuum advance, and set the initial timing to about 12 degrees BTDC. If you still have the problem then it isn't in the distributor; if it is now stable, you know what to work on.
TOHCan, did you recommend 12 degrees BTDC because that is about where the timing would be with the distributor vacuum hooked up and the car idling? I'm experiencing vaguely similar symptoms after swapping carbs to a Q-jet, and I was wondering if my vacuum advance was coming in too soon. Thanks,
vacuum must be disconnected when setting the timing, the vacuum advance will advance the timing and your adjustments will be incorrect, disconnect it and plug the vacuum line before setting to 12 degrees btdc
Thanks Blue Bird, but maybe I didn't make my question clear. I understand exactly what TOHCan meant. What I was wondering is if I was to set my initial timing to specs like usual, then hook the distributor vacuum back up--what should I get for timing with the vacuum hooked up at idle. I'm wondering if my vacuum advance is providing too much advance while I'm at idle.
Maybe I'll have to try unhooking vacuum and setting initial to 12 and see how it runs. Thanks,
Bruce, that number is kind of a baseline to start from. It should allow the car to idle reasonably well, and depending on the combo the engine might tolerate or want more. That can be from more initial if the total advance isn't too much, or from the vacuum advance as you suggest. No real hard numbers, just what the engine likes.
With a big cam, the engine will do less "hunting" if it's running just on the initial timing (ported vacuum). With manifold vacuum, if the engine speeds up slightly, the incease in vacuum may also increase the timing enough to speed the engine up, which can increase the vacuum advance, which speeds up the engine, which can start the mechanical advance to further complicate things.
Usually the problem is that the idle speed is set in neutral and both mech and vacuum advance are somewhere in the middle of their range. Then the car gets put in gear, the engine slows down, and the timing backs down, and everything drops off until the only way to keep the car running is the "two-step".
One other part of my problem was keeping the correct amount of total timing at the higher rpm. When sorting out the timing requirements, I found that when I had enough total timing for the engine to pull hard in the upper rpm, I had to turn the distributor back to restart the engine because it had too much initial. Most people have the opposite problem.
Once I "mapped" the timing that the engine wanted in steps of 500 rpm, I was able to tailor the right advance curve, and the engine started and idled nicely (considering the cam) and pulled hard all the way from about 2500 to 5500 rpm.
