Chevrolet small block 400 High idling in drive, almost stalls in park?

Question

I have an 1980 Pontiac trans am, powered by a 400 small block chevy.. Its got some problems, first of all. I have it idling in park at around 13-1500 rpms, only because when i shift it into drive, the idling drops right down to almost stalling idle at 5-600 rpms.. Its lacking in power and sometimes when I acclerate, it will backfire and hestitate.. Im guessing its a timing issue, it has a mallory twin point distributor jobbie on it, does that require a different method of timing or just the same?? because it has no vaccum advance?? No i dont much about them, but i know the local speed shop is trying to rip me when they say it needs a recondtion!!! the whole bottom end is sweet and it blows no smoke.. I really like this car and dont wanna wreck it!!!

Answer 1

The first thing I would do is can that distributor, and put a good HEI in its place. Those dual point distriburors were crap, but if they are right they are hard to beat. Keeping them right was the problem. Your timing works in relation to your #1 cylinder, so the timing is no different. You do have to set the points with a dwell meter. The dwell is usually at twice the gap. For example if the gap is .016, then the dwell would be around 32 degrees. Try setting your point gap at .018" on each set. Use a dollar bill, and close the points on the dollar bill, now pull it out. Do this a couple of times on each set. What it does is cleans anything off the points that doesn't belong there. Don't get carried away with the cam lube for the points, but use enough (on the area where the fiber on the points contacts the cam) to where it won't get hot and sling the grease everywhere. The common problem with these distributors is the fact that a lot of people forget to use the cam lube, and the points burn out very quick. The reason is the fiber that contacts the cam will wear down quick if it has no lube on it. Remove the #1 spark plug and have a friend bump the starter over while you hold your thumb/finger over the spark plug hole. Bump it just until it blows your finger off, and stop. Look at your harmonic balancer and timing marks. You should be at or very near the 0 degrees or TDC. If not move it to the TDC in the nearest direction and stop. Remove the distributor cap, but take note of where your #1 wire on the cap is at. Make a refference mark on the engine as to the correct place it is at. Your rotor should be pointing at or just a few degrees before the #1 spark plug wire on the cap. I'm thinking you may be out one notch on the distributor, but if it looks good, then make a mark at 8 degrees before TDC on the balancer, hook up a timing light, and set the timing. One thing I would do before putting the distributor cap back on is to get a hold on the top of the shaft of the distributor. Can you move it from side to side any? If so the distributor is worn out, and needs rebuilt.
Back fire can be caused by a couple of things. Bad spark plugs will do this, either they are burned up and/or wrong heat range, and wrong gap. They should be gapped at .035" no more. With dual points you don't need a vacuum advance due to the firing of the points. They fire all the way across the advance area, so there is no need to advance. They actually fire two times one right after the other, so this covers the advance area in total degrees of about 36-40 degrees of total timing. The other bad thing that can make it back fire is; the cam being worn out to the point of the lobes not opening the valves enough to fire properly. It can also be a bent push rod, or a worn out rocker arm. A vacuum gauge can tell you right away what the problem is, that is if you still have the problem after doing your timing.
Glad to help you, Good Luck!!!

Answer 2

I have never heard of a small block 400 for starters!! As far as I can remember the TA coming from the factory is this year were equipped with either 305 or 350 chevy motors, or with the 403 Olds motor. I would suggest getting rid of that distributor and going back to the original type as it was a beefy distributor which could be easily re-weighted to be timed for anything you would need. It sounds like you either have a big vacuum leak in the motor or the chain could have jumped which makes the motor act like it has a timing issue. Good luck.

Answer 3

check for vacuum leaks by spraying carb cleaner all around the carb and vacuum lines.When the carb cleaner hit where its leaking your engine will rev up a little