HELP-Car spitting and sputtering at me

[BLACK MOON]

Well I'm going to start a new post because this problem has gotten worse. This started after rebuilding my 327/300 hp motor. I removed and cleaned all electrical connections before reinstalling the motor. Now setting the timing to a good running condition has been impossible. Well I broke down and took it to a reliable shop and low and behold the motor has the wrong timing cover and welded tab on it. The guy puts in heavier springs and corrects the timing. The car runs ok for about 10 minutes and then starts hesitating, pulsing, spitting thru the pipes and what sounds like backfirring. The sidepipes makes this racket sound like gunfire and the pedestrians don't seem to care for it. This occurs at a steady speed or decelerating. Acceleration is strong and no popping. I've changed coil, and installed hotter plugs at his suggestion but neither helped. I'm using an MSD tach drive dist. and a 6A box. Does the box need to be grounded? Could I have missed a ground when I detailed the engine compartment? We're all scratching our heads and butts trying to figure this one out. Any help would be appreciated. We are pretty confident it's electrical but that about I know. And we could be wrong.:crazy

 

[BLACK MOON]

Why would you move the distriburator a tooth. Wouldn't that be the same as turning the dist.? Rebuilt motor, new timing gear and chain.
Thanks

 

[allcoupedup]

Blackmoon,
When you rotate the distributor, you are only rotating breaker plate, the points, and the cap. The mainshaft and therefore rotor remains stationary. When you rotate the housing all you are doing is changing the relative relationship between the rubbing cam and the points --- the rotor doesn't move. If you think about it, the mainshaft (and rubbing cam) are connected to the camshaft via gears so moving the housing cannot move the mainshaft and the cap.

Have you checked your dwell at idle and at high RPMs? If it changes much you need a distributor rebuild.

hope this helps.Brian

 

[BLACK MOON]

My point was what difference does the position of the mainshaft make as long as it lines up with number one at TDC. Do you see what i'm saying. Pulling the dist and rotating it a tooth or 180' doesn't matter if you rotate the housing with it. Otherwise moving the shaft a tooth will only cause you to rotate the housing. I hear you but I don't see the difference. It's a MSD electronic breakerless and pointless dist. No dwell.
Thanks for the help.

 

[allcoupedup]

You've probably been over this but have you ever considered checking your carburetor. A lean condition can cause backfiring. Since your car accelerates nicely, I'd take a quick look at the idle screws and play around with them to see if anything changes. A small vacuum leak would cause this same condition. Since idle produces the highest vacuum, the leak may only be signifigant enough to cause a problem at idle.

just a guess.


Brian

 

[BLACK MOON]

It's set at 8' btdc and 32 total byt we've played with several variations and the problem is still there to different degrees. Only seriously retarding the ignition helps and but it still pilses and pops.
Thanks everyone. This forum is great.

 

[Mikey1]

Have you checked to have the correct type balancer on your engine....GM did move the mark....guess around ´70 by 10 deg.

Did anyone work to the distributor ? The drive gear could have been mounted wrongly....there is a small dent that has to be lined up with the rotor contact....

What about points.....I've seen all sorts of sh*t with this crap !

 

[Subfixer]

I had a similar problem with my stock 327/300. It would spit and stumble while cruising, accelerated well, and noisy backfiring when decellerating. The problem turned out to be a broken diaphram in the vacuum can. This kept total advance lower than optimum and caused a small vacuum leak. Once I replaced the vacuum can, all my problems went away.
Just because it's a new distributor, don't assume the vacuum can is good. One good backfire and the diaphram is history.
You can check it by watching the initial advance at idle while removing and replacing the vacuum house to the can. If the timing does not change, then the can is bad or the mechanism is binding.
Hope this helps.

 

[BLACK MOON]

That makes sense. I'm almost starting to think it mite be the carb. I'm going to try a dist change and was planning on going to a Holley Street Avenger which I have already purchased. I just wanted to fix this issue first. The car does run better with the vacum advance disconnected.