[curtis73]

Here is the back story. 67 Lemans 326. It had a complete tune up including a carb rebuild, then the previous owner parked it for 8 years before I bought it.

Drained old gas out of the tank (probably left 1 gallon in the bottom)
Refilled with 12 gallons of new
new cap, rotor, plugs, points
found that the vac advance diaphragm was broken so I replaced it.
Set dwell and gap (turn in until misfire, then back out 1/2 turn)
timed to 6 degrees BTDC with the vacuum line off and the hole plugged

Starts and runs great. I have driven it this winter in 10 degrees and this spring in 90 degrees. Always starts, WOT is perfect. Always around 10-15% throttle, it dies. I can usually keep it running by either stabbing the throttle to get past it or feathering the throttle to get a couple little acc pump squirts. Very important to note that it doesn't seem to be an acc pump issue since it doesn't recover AND the same thing happens when decelerating. If I'm cruising at 35 and let up on the throttle, it still sputters and dies when I get to that throttle range.

So then I did the following:

replaced every vacuum line
tested for vacuum leaks with brake cleaner
verified timing advance with the vacuum line on and off - tests good
Pulled the carb apart and verified no throttle shaft play, cleaned every single orifice, verified correct gaskets.

Same exact problem. I then pulled the carb apart again and re-replaced the accelerator pump. I verified that it is pushing a good stream the instant the throttle is touched and for a good complete stroke. I tested plug wires and they have good even continuity. I tried using jumper cables to ground the block, no change. I tried bumping up the timing to 12 degrees. No change other than getting detonation.

I took a video of it. Link below. I tried doing a video while driving so you could experience the decel sputter, but you can't hear the engine.

What am I missing? Ideas?

https://www.youtube.com/watch?v=vt6CE77EGSE

[jd66]

contact this guy, knows his stuff. mike@pontiactripower.com jdgrim66 gto

[Kenth]

Carb is calibrated for yesteryears fuel.
I would open the idle tubes 2-3 thousands of an inch and use a couple of thou. larger main jets.

[fyrffytr1]

How about the distributor advance plates? Could the bushings be worn or the arms not even moving?
I don't have much room to talk because I am chasing the same gremlin with a brand new 4-bbl quadrajet. WOT is amazing but it falls on it's face if I just ease into the gas.
You might try backing the idle mixture screws out two full turns from where they are now. If that solves your problem then look for a vacuum leak.
I did that and the car ran great so I checked all possible sources for a leak. I replaced the vacuum hose to the transmission line, tightened the carb down as much as I dared to and put hose clamps on the brake booster line because it pulled off the fittings easily and I didn't have any new line to replace it with.
That helped a lot and I turned the screws back in1 1/2 turns but I still have a stumble. Any adjustment to the idle mixture screws does nothing now so I know a vacuum leak was part of my problem.
My next step will be to replace the fuel pump with the correct one. The one on my car is for non A/C and my car is air conditioned. There is a big difference is the two. If that doesn't do it I am not sure where to go.

[curtis73]

Originally Posted by fyrffytr1

How about the distributor advance plates? Could the bushings be worn or the arms not even moving?
I don't have much room to talk because I am chasing the same gremlin with a brand new 4-bbl quadrajet. WOT is amazing but it falls on it's face if I just ease into the gas.
You might try backing the idle mixture screws out two full turns from where they are now. If that solves your problem then look for a vacuum leak.
I did that and the car ran great so I checked all possible sources for a leak. I replaced the vacuum hose to the transmission line, tightened the carb down as much as I dared to and put hose clamps on the brake booster line because it pulled off the fittings easily and I didn't have any new line to replace it with.
That helped a lot and I turned the screws back in1 1/2 turns but I still have a stumble. Any adjustment to the idle mixture screws does nothing now so I know a vacuum leak was part of my problem.
My next step will be to replace the fuel pump with the correct one. The one on my car is for non A/C and my car is air conditioned. There is a big difference is the two. If that doesn't do it I am not sure where to go.

If I come out just a 1/2 turn on the idle screws it barely runs... bad enough that I can't really test it because it keeps dying. I tried it 1/4 turn out and it didn't solve the issue... which means it either isn't the problem, or I can't get them out far enough to cover the vacuum leak before its too rich at idle.

The advance weights move freely. I verified it by hand and also revved it with the vacuum hose off and watched the timing light. At very fast idle its at about 20 degrees advanced, so they seem to be doing their job. The stumble seems to be happening before the weights should be advancing, but its a good idea.

One of my next steps is to pull the throttle shaft and put a mic on it all around to see if its worn in an oblong shape. That might make it seem tight but still have a leak. I tried revving it up a bit to the point where it stumbles and soaked the shaft area with brake cleaner and it didn't change, but its possible its still an issue.

[fyrffytr1]

How far out are your idle screws now? I was telling a mechanic about my problem and about using brake cleaner to look for vacuum leaks around the intake. He said to punch a small hole in a plastic coke bottle and dribble water along the intake. If there is a leak it will suck the water in. There won't be enough water to harm anything though. I haven't tried that yet because I am down in my back this evening and pain pills don't mix with mechanicing!