ricknhis69 said: I know you said you had your Rochester rebuilt, BUT, this sounds an awful lot like a carb problem. It sounds like it might be running too lean. That could be why it runs ok when the choke is closed. It's probably just a matter of doing some tuning.

Hmm....well, I just checked the dwell and timing. I guess the mixture could be too lean though. But why is it that it idles fine in Park or Neutral, and dies only when I put it into Drive? Seems like if the mixture was too lean, the engine would die out even idling in Park?
But maybe not? I know the choke is working. I see the throttle plate go vertical when the motor is warmed up and is closed when cold.

Steve

Let it warm up. Use your hand, a rag, or the choke plate and choke the engine a little bit at a time. You can also add small amounts of carb cleaner. No matter which way you chose this richens the fuel mixture. If the engine speeds up, it's running too lean. Lean can be due to vacuum leaks anywhere or carb adjustments. Don't richen it too much or it will bog down and stall. Just go a little bit at a time.

You say it dies in drive but not in park or neutral? It idles faster in drive and neutral, and kicks down in drive. It does sound like you have a lean idle condition. Does it tend to bog down a bit when you try and accelerate?

It sounds like either there is a vacuum leak, or more likely, the primary jets are too small. Is this the original carburetor? Has the cam been changed to a more aggressive profile? There may be a mismatch between the jetting and the cam (I know from personal experience). Try changing to the next size larger jets (or maybe even two sizes larger), and see if this cures your problem.

Yep, it bogs down when I try to accelerate. But only after the engine has almost fully warmed up. When cold it accelerated fine. So the temperature of the engine has something to do with the problem. I definitely agree that something is causing it to run too lean when the engine is fully warmed up and in drive. In Park or Neutral, it's fine.

I'm going to try to change the fuel filters this weekend. The car has been in storage for around 13 years, so I'll be the filters have junk in them.

Wouldn't a vacuum leak cause problems whether or not the engine is warmed up or cold?

The cam is original and the carb is the original Rochester Quadrajet.

--Steve

|UPDATED|12/4/2003 11:20:53 PM (AZT)|/UPDATED|

I had similiar problems with my Q-jet, took the easy way out and changed it out with a holley and haven't had any problems since. I'm thinking about rebuilding the original Q-jet and putting it back on though.

When there is no load the engine will idle ok on a lean mixture, as soon as you put a load on (putting it in drive) the lean condition will lead to a stall. The carb needs to be set to run rich enough to deal with any situation but it shouldn't be set any richer.

So I changed my fuel filters this weekend. But I'm still having the same problem. The engine runs fine (both at idle and actually under load driving) when the motor is cold. But as soon as it fully warms up, and I shift it from P or N, to 3, 2 or 1, the engine idle speed drops way down and the engine sputters and dies.

So yep, must be some kind of vacuum leak. My PCV valve looks fine and it rattles.

So yikes, how do I find a vacuum leak? I've looked over all the vacuum lines to the headlights and wiper door and they all look fine. My headlights and wiper door work great. Is there a common vacuum line that leaks on these cars? If so, which one or ones?

Also, after changing the big fuel filter canister on my 327, I'm getting a small fuel leak from the bottom fitting. I tried using plumbers pipe thread sealant, but it didn't do the trick. Should I try silicone tape?

Thanks,
Steve

Hello Steve,

Have you adjusted the idle air screws at the front of the carb? Rough adjust them 2 1/2 turns out from bottom. Then use a vacuum gauge to adjust each for max vacuum. If you have adjusted the idle air already, but with no discernable effect, pull the screws completely out and make sure they are intact. I have heard of them breaking in the seat. This would give a lean condition.

You might also look at the vacuum gauge for a jumpy needle. At idle, this may mean bad valves and the leak is inside the engine. You can check valve lash, but you should have hydrolic lifters and they typically hold lash.

To eliminate leaks in the vacuum accessory circuits you can pull the line off the back of the carb. If this helps then look at the vaccum resevoir canister. It is located in the fender drivers side back of the wheel well. Often these can rust through. Check it with the engine off with a hand vacuum pump.

Alex

alexnelsen said: Hello Steve, Have you adjusted the idle air screws at the front of the carb? Rough adjust them 2 1/2 turns out from bottom. Then use a vacuum gauge to adjust each for max vacuum. If you have adjusted the idle air already, but with no discernable effect, pull the screws completely out and make sure they are intact. I have heard of them breaking in the seat. This would give a lean condition. Alex

Nope. Haven't adjusted them yet. I guess I really should eh? Should I adjust them with the engine warm and at idle? Or with engine warm and transmission in Drive? I have an automatic and the sticker in the engine compartment says my idle speed should be 600rpms with engine in DRIVE.

Where do I connect the vacuum gauge on my Rochester carburetor? I see a vacuum tube going to the vacuum advance on the distributor and a tube to the PCV valve.
Where do I connect the vacuum gauge to? You mention back of the carb?

alexnelsen said: Hello Steve, To eliminate leaks in the vacuum accessory circuits you can pull the line off the back of the carb. If this helps then look at the vaccum resevoir canister. It is located in the fender drivers side back of the wheel well. Often these can rust through. Check it with the engine off with a hand vacuum pump. Alex

What pressure should I pump up the canister to? I don't want to over pressurize it, do I?

Thanks,
Steve

Hello Steve,

Make sure the engine is warm, choke open, car in park. Connect the vacuum gauge to one of the ports on the base of the carb as this will read manifold vacuum.

There is a port at the base of the carb, towards the firewall (back). If not then there is a port on the manifold between the carb and distributor that the main vacuum is taken for the accessories. If it is on the manifold, make sure there is a plug or cap on the rear carb port.

On the vacuum canister, use a hand pump such as the Mity Vac. Pump it to 15-20 in/hg and watch to see if the needle drops once you have stopped pumping. If you have isolated the canister and the needle drops replace the can. Also feel free to call 303-888-6577 (Vette Specialties) if you have any questions that I can help with over the phone.

Alex