[pontiaclady]

66 GP - starts fine, smooth, but will not stay running unless keep gas petal down or feather it. As soon as try to idle, stops. Have been thru the fuel system. Gas tank, sending unit restored, tri-powers rebuilt, new fuel lines - pump working fine and gas getting to carbs no problem. played with idle screws, but even when at a too high idle (car roaring) it will die as soon as foot off gas. someone in the past had put a resistor block on firewall that has a wire from starter to coil, then to resistor and back from other resistor plug to negative coil wire then to distributor. My 65 2+2 does not have this so unhooked resistor and it acts the same. would a bad coil affect running after started? Not sure what else to try?

[Deadhead]

2 thoughts: Carb linkage/idle screw on linkage not adjusted right or maybe Vac. leak? Try disconnecting all Vac. lines & plugging w/ a screw etc. & see what happens.

Have had this happen before, but will have to think longer to remember the cause in my case.

[pontiaclady]

Thanks - tried not any difference, but some of the hoses are very brittle/old - I'll try replacing and see if there might be a crack I can not see. They need it anyway. next weekend project.

[mkoser]

I vote vacuum leak 100%. While the engine is revving, it produces enough vacuum to pull fuel/air through the carbs. At idle, the leak is so bad, that it's pulling vacuum through the leak, and not the carbs.

MK

[stevep]

If you block the air horn on all 3 carbs and the car stays running, you have a vacuum leak.

Try disconnecting and blocking the PCV @ the intake.

[Deadhead]

I hate to say it, but if you have trips, you might have to do a block-off plate on the 2 outboards & run with center only to narrow it down. Block everything off on vacuum side as described above in addition to that & see if it solves Prob. It's part of the joy of 3 carbs! The base gaskets can leak & cause a Prob.

[pfilean]

Get it warm and running as slow as it will continue to run. Spray a little choke cleaner at various places where it might have a vacuum leak. Carb bases, intake manifold to head, hoses etc. When you hit the place where it is leaking the engine speed will increase and smooth out momentarily. Even a power brake booster diaphragm that leaks can be a problem.

[pontiaclady]

Thanks much for all of the advice. Has been very helpful and have fixed some of the issues, but still not quite there. I'm sorry to ask for such basic advice, but would be grateful for some more assistance - helps me learn and keep the pontiac going.

I checked for manifold leaks (none), replaced all of the engine vacuum hoses and there were two that were really brittle and had cracks. The engine now idles ok - the vacuumn gauge is at about 16 in. hg when warmed up. The engine runs fine until put into gear, it then slows and stalls. Increased the idle, but did not make much difference and then when turn ignition off - diesels and knocks. Have to turn off in gear or knocks. Put idle back down where vacuum is at 15 in. hg on the vacuum gauge and it turns off ok without knocking, but will not run in gear. So now it is at a point where it will run at idle, but not in gear.

Dont know if makes difference or not, but plugged end leading to the vacuum advance at the distributor to disconnect, car ran the same.

Anything else to check?

[mike nixon]

Have you checked the ign timing? Do it with advance hooked up and not.

Also if it's an suto car, make sure the vac lin to the trans hasn't come of the modulator causing it to suck air down low.

Mike

[pontiaclady]

I have not checked the timing - quick question, would it be the same degree timing with the advance on and off? It is an automatic and have replaced the hose to the modulator on the transmission (was oily).

[mike nixon]

No, normally the older cars run Manifold Vacuum which will advance the timing at idle. Unhooked will drop the timing about 12 degrees. I like 32-36 degrees of total advance, mechanical,base and vacuum combined. That'll change depending on Cam, Head flow numbers, ect. Also be sure the mechanical advance isn't stuck. It needs to advance and return freely. Dwell should be set @ 28-32 degrees. If it's off it will affect timing and that in turn will afect the idle.

[Deadhead]

To Mike's point - take off the Dist cap & see if the weights and springs are free. They get frozen/rusted in case you are not familiar with these.

Also, even if hose is good could be that modulator is toast.

[stevep]

If the modulator hose is oily, I'd say that the modulator is bad. There shouldn't be oil in the hose.

[mkoser]

Does it stall when you shift it into gear, or when you step on the brake?

Maybe your brake booster is bad, and you lose vacuum.

Just a thought.

MK

[BVR421]

Is this a new startup or a new problem that ran well in the past? If so what have you changed since it ran well?

Every tuneup begins with ignition, 9 of 10 carb problems are actually ignition problems, it took me many years to understand this concept now its a mantra LOL
Once you have verified 30º dwell, 6º initial and no problems with wires, weights etc under the cap, reconnect vac advance and set idle speed to 650 with motor thoroughly warmed up. Who knows it might help.
It may be informative to, with a helper, have a timing light on while slowly reducing throttle speed to the point of faltering. That would highlight any weird ignition short as rpms change.

Sounds easy when Im way over here typing LOL

[Deadhead]

Originally Posted by stevep

If the modulator hose is oily, I'd say that the modulator is bad. There shouldn't be oil in the hose.

Steve - Will this produce white Exhuast smoke the majority of the time?

Might help diagnose.

[stevep]

Originally Posted by Deadhead

Steve - Will this produce white Exhuast smoke the majority of the time?

Might help diagnose.

Yes it could, but it depends on how bad that it is sucking fluid. I have taken many vacuum hoses off cars with leaky modulator diaphrams that did not smoke.

[pfilean]

The engine now idles ok - the vacuumn gauge is at about 16 in. hg when warmed up. The engine runs fine until put into gear, it then slows and stalls. Increased the idle, but did not make much difference and then when turn ignition off - diesels and knocks. Have to turn off in gear or knocks. Put idle back down where vacuum is at 15 in. hg on the vacuum gauge and it turns off ok without knocking, but will not run in gear. So now it is at a point where it will run at idle, but not in gear.

Not sure what year they started using them but by 68 a lot of cars had an anti-diesling solenoid. It's on the throttle linkage and about the diameter of a half dollar and 1 1/2 inches long with a single wire hookup. The solenoid extends when the key is on and retracts when the key is shut off. The idle adjustment is on the solenoid plunger and you adjust the idle with the key on (of course - cause it's running). Then when the key is turned off the plunger retracts to allow the throttle blades to close completely to shut off any air flow that might cause diesling. If this solenoid doesn't work then you will get some of the symptoms you describe.

[pontiaclady]

Thanks all - sounds like I have a lot of things to check. I'll start with the timing/distributor etc. Will tackle next week - going to check out Norwalk.

Actually car has been running crappy for a while now. Started as problems with running terrible when got hot, then stalling whenever at an idle unless under power. Took to mechanic, got better, but idle was too high and dieseled and rough. They did checked over etc...nothing changed. Then I got the 61 Tempest and neglected the 66 GP by letting it sit too long. It always had tripower issues and sitting made them worse. Ended up with the front carb becoming a drinking fountain and gas leaking into valley pan from several spots - so decided to bite the bullet and took off all 3 carbs and sent to Mike Wasson. He found a lot of issues and clogged areas. Put back together, dropped gas tank, had it redone, had sending unit rebuilt, cleaned out fuel lines, replaced all rubber fuel lines. Ran much better, but then ended up with my first post that started this thread. I made assumption that mechanic checked timing and ingition, but after going to parts house several times this weekend because they gave me wrong parts - I am learning not to take it for granted....

Trying to do more inhouse to save money and have been finding some of the mechanics out there only know how to hook up the diagnostic and do not know how to do anything on these old cars. I've got a great book called AutoRepair for dummys from 1976 and that with the chassis manual and help from you all at the forum seems to be working out pretty good so far. Thank you very much for all your help.

[BVR421]

I've got a great book called AutoRepair for dummys from 1976 and that with the chassis manual"

good to have those and check also used book store and Amazon and ebay for a MOTORS Manual that covers 66 they go in 8-10 yr increments of coverage. A greasy dogeared copy will go from 25-40 bucks. Not because they are antique but because they are so darn useful. A lessor but still effective manual is the Chiltons, often for 15$
A CD copy of the original Pontiac factory manual can be had for $35-50. Public Library have manuals you cant check out but can make copies of pages from.