Topic: Need help, please. Engine not running good.

[1976T/A]

Need some help. My car is not running real well and I’m not sure where to start. I suspect my problems are ‘carb’ related but I’m not sure.

Car is a ’76 T/A with L78 400, auto. 48,000 original miles. Engine has never been apart and the only mods have been the removal of all emissions related components and the addition of headers and 3.42 rear gears. Everything else is stock.

I recently had the engine bay apart to do some detailing so I changed the plugs, wires, distributor cap, and coil. The hot air choke had been disconnected by the previous owner so I hooked it back up. The engine had been running ‘fair’ before I did any of this so my hope was that it just needed a mild tune up (guess I was wrong).

The carb was rebuilt about five years ago but I do not know who did it and I’m pretty sure it was a ‘stock’ rebuild. This was before I really started learning about Pontiacs so my ignorance is the culprit for not being more concerned about “who” did it and “what” they did.

Here are the symptoms – fires up after about three cranks. I need to keep my foot on gas pedal for a couple of minutes until it will idle on it’s own @ 500rpm. It used to idle at 750rpm before I hooked up hot air choke. When I first take off, it sputters and even mildly backfires a couple of times. After the engine warms (160 degrees), it starts to run better but still not great…..and it is sucking down gas big time. Throttle response is very poor until engine warms but is still poor even after it does……UNLESS I jump on it. If I punch it, it will take off like nothing was wrong…..and if I’m doing, say 40mph, and I go WOT, it kicks down like it should and goes like a bat out of he**.

So, to summarize, it runs like crap when until it warms and still rough even when I’m just driving it around…..BUT….seems to be ok at WOT.

Any ideas, suggestions would be GREATLY appreciated. I can diagnose and correct some basic problems on my own, but when it comes to this kind of stuff, I don't know where to start or what to do.

Thanks !!

[eroc022]

sounds like an ignition issue, somewhere your timing, or something isnt fully working to its potential..... thats where i would start

[ponchonutty]

You may have a few things going on.  I ran into this very issue when I did about the same thing to my car a few weeks ago.  I didn't end up replacing the cap/rotor/or wires.  I did however had it all off while I was painting.  The only thing new was that the carb was rebuilt and new plugs.  When I got it back together it would behave like you stated but it still even at WOT seemed a little off and would backfire a bit.  Ended up having to reset the timing AND I had plug wires #2&4 swapped.
Like you, I had most of everything unplugged from one of the previous owners.  The choke tube was there but it was rotted apart.  Also, the gasket inside the bowl that houses the coil spring had almost half of it missing.  All of this was corrected so I had a lot to mess with to get it right.  I had to readjust the idle mixture along with the idle and fast idle.  I still need to get the timing on a little better than what it is but it's sooooo much better than before.

[jphillips3333]

Carb/tuning issues - quadrajet?
Dirty fuel filter?  Sounds like you get fuel flowing into the secondaries and it's there when you need it.

Disconnect the hot air choke and see how it runs ... sounds like it's starved for the right air/fuel mixture.

[1976T/A]

Yes, it's a quadrajet.

I've checked and re-checked the wire order to make sure it's correct.

Already tried plugging the hot air choke tube...no better.

Guess I'll have to get out the timing light and my quadrajet book and start trying to narrow it down. Was just hoping that perhaps my particular symptoms would point to something obvious that someone had experienced.

My gut is telling me it's the carb that needs some adjusting but I hate guessing.....and I hate the thought of taking it to a shop even though I know the people where I go. So hard to find someone who *really* knows these old cars....at least around here.

Thanks for the feedback. Much appreciated!!!!!!!!! 

If anyone else thinks they know what is causing this, please let me know.

[stimpy]

sounds like a  timing issue ( late timing or worn chain  ) , put a vacum gauge on it when its warm and see what it does ,

[4speed76]

Did you happen to gap your plugs when you put them in?  Carb might need to be adjusted, as well as timing.

[1976T/A]

I gapped the plugs at .50

How do I go about checking to see if my choke is functioning properly?  I have a suspicion it may not be disengaging when the engine is warming.

[4speed76]

see if disconnecting the choke makes any difference?

[Grand73Am]

I agree that the choke could be the problem, since it's something you changed. It had been disconnected before and you said it was running "fair" that way. Then, you've hooked it back up and it runs poorly and sucks the gas. Sounds like the choke isn't opening. I'd disconnect it again and wire it open, then see how it runs. That's a quick and easy thing to do to see what difference it makes. Just leave it that way if it runs good.

[1976T/A]

Thanks for the input, guys!!

Choke seems to be functioning properly. Must be something in the timing. Half thinking of maybe buying a new aftermarket distributor and installing. When I had the cap off a month or so ago, there was some noticeable rust build up.....which might be contributing ??

Dang idler pulley on the front of the engine almost completely blocks the timing mark. Going to be hard to get a good angle with the timing light !!

[stimpy]

how many miles on the engine ? as replacing the distributor might not be the problem (GM HEI's are one of the best ignition systems out there ) , pontiacs are hard on timing chains for some unknown reason and if your still running the original one its way overdue to be changed as the plastic they put on the teeth drys out over time and starts to flake off  and will retard the timing as the chain stretches and then one day it will slip all together when it breaks off ( the nylon cover ) the rust you see in the cap is not really rust its Ionized particles in the air  ( the dust and stuff in the air ) the high voltage zaps it and will start to turn it into carbon that will conduct electricty and cause misfires and ultimately fry the coil out , just buy a new cap with a carbon resistor stub and rotor  ( I recommend either Accell , MSD , or a Standard auto parts ( Napa ) cap with Brass terminals as the aluminum ones are Junk and form oxide layers on the innner terminals and act like a resistor and will cause tracking as the aluminum burns from the high voltage discharges and sprays onto the inside of the cap ) , first check the chain for play (its easy and you don't have to pull the cover off  and you do it when replacing the cap and rotor   ) ,what I did to make it easier to time the motor with alot of pulleys was to extend the mark with a white  painted  line onto the back of the pulley ,and over the pulley grooves but if trying to see the marker is a pain trypainting  it flat black  so it wount reflect back light making it easier to see and use flat white on the numbers and lines)        

[1976T/A]

I was out in the garage last night looking at the timing mark again. With the idler pulley in the way, I can’t even see enough of the mark to set the timing (it blocks 85%-90% of the mark). I don’t have a service manual but I would really like to know what GM’s instructions were for working around that obstacle. I can see I am going to have to get creative and maybe do something like stimpy did……although I can’t seem to visualize what you did, stimpy….even after reading it a couple of times??? By the way, thanks for the input !! The engine has 48,500 miles on it. I just put a new cap and coil on about 100 miles ago.

I am still learning about making carb and timing adjustments in order to improve performance. I really envy those of you who understand this stuff as well as you do. I know how to operate a timing light and do some basic tuning, but when it starts involving changing springs, weights, center plates, etc….and then trying to dial-in a “vacuum + mechanical” that the engine responds well to, I start realizing just how much of a challenge this can be. I’d be happy if the thing just ran good…..I’m not looking for a perfectly dialed in beast that blows the doors off of everything.

[brian c]

Here's what I did for mine to make it much easier to see.....

I'm running a chrome harmonic balancer which is a royal pain to see any of the cast in markings. I bought some timing tape for Pontiac engines. From underneath the car, I lined up the timing tape with the cast in markings and then stuck the tape to the balancer. There was a lot of extra tape so I cut off what I didn't need. Much easier to read now.

You could do the same for painting a line on the pulley - procedure Stimpy mentioned. Just use a good shop light while you're under the car so you can see the markings to carry over to the pulley.

And please be careful when you're under the car. Make sure its properly supported BEFORE you crawl under there

[ponchonutty]

I 2nd about being carefull under there.  Almost 2 years ago I about ended it all when I had a truck go on top of me.  Luckily I only ended up with 8 broken ribs, bruised lung and kidney.