Quadrajet Idle Problem

[67_Eldo]

A test to which I almost resorted was a "smoke" test. There are a variety of high-tech to extremely-low-tech ways of getting smoke into the engine and some folks swear by smoke tests. My friends, however, are more prone to use the squirt-carb-cleaner-everywhere-and-listen-for-changes-in-the-idle test (which ultimately worked for me).

A smoke test has the advantage of pointing out leaks in unlikely spots (e.g. in the intake-manifold gaskets).

Here's one short smoke-test writeup. There are about 1000 smoke-test videos on YouTube.

https://www.tomorrowstechnician.com/use-a-smoke-machine-to-locate-a-vacuum-leak/

["Cadillac Kid" Greg Surfas 15364]

FWIW My 66 (with a 67 intake and QJ) ran best at 10* initial timing with the vacuum advance (which I would suggest you check) hooked directly to manifold vacuum and running 93 Octane gas.
Greg Surfas

[MikeLawson]

Here is an update on my progress:

I have replaced the distributor cap, rotor and points.
Checked ignition wire resistance and coil resistance, all are OK.
Cleaned all ignition connections at coil and in distributor.
I replaced the AC44 spark plugs with new AC R43S plugs gapped @ .035
Set dwell at 30 degrees and rechecked timing. Advanced timing about 3-4 degress to obtain best vacuum reading, now at 8-9 BTDC.
Adjusted idle screw to get best vacuum reading.
Disconnected vacuum lines and plugged ports, no change noticed. Sprayed carb cleaner around intake manifold, no change noticed.

Idle has improved a little bit but it still idles best at about 750 rpm in park. Vacuum gauge reads between 19-20 in. but still needle still has a vibration.

I can live with it the way it is but I'm very willing to try other things that may be suggested here.

Thanks for any other input.

["Cadillac Kid" Greg Surfas 15364]

Mike,
Forgive me if this has already been discussed/done, but do you have the SS shim under the carburetor?
Greg Surfas

[67_Eldo]

I don’t know if solving the problem is worth $300-$400 to you. If it is, I’d try the “remanufactured” carb route. It seems as though you’ve covered everything else.

Except â€" long shot here â€" the transmission’s vacuum modulator. My transmission was rebuilt almost three years ago. Two years later â€" just as the repair warranty was about to expire â€" I accidentally pulled off the vacuum hose that ran from the carb to the transmission. As I was reattaching it, drip! A drop of transmission fluid came out of the vacuum hose! Not good.

So I took the car back and got the vacuum modulator replaced under warranty. It took him two months to perform that 15-minute task, so the joke was on me. But at least I had a fully functional vacuum modulator again. 

[MikeLawson]

Mike,
Forgive me if this has already been discussed/done, but do you have the SS shim under the carburetor?
Greg Surfas

Yes Greg, the stainless shim is in place. I used a new high-temp composition gasket below and above the shim.

[Greg C]

my 472 had a slight  rough idle,slurping sound from tailpipe and vacuum gauge fluctuated
it was a bad intake valve

[Cadman-iac]

The fluctuating needle on your vacuum gage is a clue that you have a mechanical issue in your engine.  My guess,  you have a carbon build up on the heads of the intake valves that's causing an uneven flow into your cylinders. Have you tried using a cleaner in your fuel system to get rid of any build up?
If your valve seals are worn, it allows a small amount of oil to run down the stems over time and the heat will "cook" it onto the top of the valve. In worst case scenarios it looks like a "carbon copy" of the intake runner,  and it severely restricts air flow.
There's an additive called 44K that's made by a company called BG and I've used it several times for just such a problem with great results. (Not the severe case obviously,  but build up nonetheless).
It will work slowly when added to the fuel, but if you want faster results,  it can be added through a vacuum hose inserted into the can and drawn into the engine.
You Let it draw in about 2/3's of the can before you take the rest and pour it down the top of the carburetor and let it stall the engine. This gets a concentration of it on the valve heads. Let it sit then for about 30 minutes,  then start it up again and rev the engine to clear it out. It will smoke like a locomotive for a bit, but it will clear up after a few minutes.
This is a chemical fix for a mechanical issue,  but it's a lot cheaper than replacing the valve seals, and even cheaper than a valve job. Obviously it won't prevent it from happening again,  but if it works,  it will tell you what the problem is.
The last time I bought a can of it, it was around 20.00 bucks, and you will have to buy it from a shop. It's not sold directly to the public, although the shops will sell it to you.
Just food for thought.
Rick

[67_Eldo]

Coincidentally, the BG product was mentioned on the most recent episode of the Car Wizard.

https://www.youtube.com/watch?v=8zmXyB38mRg&feature=youtu.be&t=320

[MikeLawson]

I might give the fuel system cleaner a try. My compression test results were fine, all cylinders between 180-185psi and pumped up quickly. Spark plugs were all clean with no signs of oil burning. Could it be as simple as a leaking intake manifold gasket. I did try to check for this but it isn't possible to reach all the areas. Replacing the intake manifold gaskets shouldn't be too difficult on this engine.

[Cadman-iac]

that's typical for this problem. The cranking speed is slow enough that it won't show up.
The product in the video must be a new can size. It's about twice the size as the one I used to get. And the one I get has a pop and peel top on it so the whole top comes off.
Regardless,  it should work on the problem. Good luck with it, and please let us know how it goes.

Rick
PS:
You do know that it's not necessary to remove the intake manifold to use this product on your engine. If the carbon buildup is not so bad as to block off the runners, then just drawing it into the engine via a vacuum hose will work.  You just need to be sure that you pick a vacuum source that will distribute the cleaner to all 8 cylinders. The PCV port is a good one, it's right up front on the carb, and it's big enough that it gets into both sides of the intake.
I also watched that video that 67 Eldo posted the link to, and on the car he's working on, the runners in the heads were very short and easy to get at the valves.  The 472 won't be as easy because the runners are a lot longer.
For the price,  i would personally try it through the vacuum hose first, and then if there was no improvement,  then take the intake off and have a go at it that way.

[MikeLawson]

Rick,

I do understand that it is not necessary to remove the intake manifold in order to use the fuel system cleaner. I was thinking about removing it in order to replace the gaskets to eliminate the possibility of a leak there. I should also add that this engine only has 46,000 miles on it and other than the imperfect idle, it runs great.

[J. Skelly]

The fluctuating needle on your vacuum gage is a clue that you have a mechanical issue in your engine.  My guess,  you have a carbon build up on the heads of the intake valves that's causing an uneven flow into your cylinders. Have you tried using a cleaner in your fuel system to get rid of any build up?
If your valve seals are worn, it allows a small amount of oil to run down the stems over time and the heat will "cook" it onto the top of the valve. In worst case scenarios it looks like a "carbon copy" of the intake runner,  and it severely restricts air flow.
There's an additive called 44K that's made by a company called BG and I've used it several times for just such a problem with great results. (Not the severe case obviously,  but build up nonetheless).
It will work slowly when added to the fuel, but if you want faster results,  it can be added through a vacuum hose inserted into the can and drawn into the engine.
You Let it draw in about 2/3's of the can before you take the rest and pour it down the top of the carburetor and let it stall the engine. This gets a concentration of it on the valve heads. Let it sit then for about 30 minutes,  then start it up again and rev the engine to clear it out. It will smoke like a locomotive for a bit, but it will clear up after a few minutes.
This is a chemical fix for a mechanical issue,  but it's a lot cheaper than replacing the valve seals, and even cheaper than a valve job. Obviously it won't prevent it from happening again,  but if it works,  it will tell you what the problem is.
The last time I bought a can of it, it was around 20.00 bucks, and you will have to buy it from a shop. It's not sold directly to the public, although the shops will sell it to you.
Just food for thought.
Rick

GM sold the same product, and called it Top Engine Cleaner.  I used it on my '71 Eldorado.  I don't know if it is still available at GM dealers, and I sold the car in 1987. 

[cadillacmike68]

600 RPM in Drive is a good starting point. Dwell at 30, AC OFF, Vacuum advance disconnected and plugged, Timing at the spec for that year (0 to 3 to 5 Deg BTDC - whatever your year specifies) and idle screws backed off 1 & 1/2 turns from a 20 RPM lean drop on each side.

[MikeLawson]

Today I figured I would try a simple cylinder balance test. I disconnected one ignition wire at a time and observed the RPM drop.  All 8 cylinders were the same so it doesn't seem like my problem is with any particular one. I'm thinking about pulling the intake manifold and installing new gaskets just to eliminate them as a potential source of a vacuum leak. Does that seem reasonable?

["Cadillac Kid" Greg Surfas 15364]

Be sure and check the PCV connections in the valley cover under the intake
Greg Surfas

[67_Eldo]

Does that seem reasonable?

Other than the fact that it's a fair amount of work, it seems reasonable.

I had the intake-manifold gaskets replaced three years ago. There was apparently a tiny leak or two in those, although there were so many other leaks that the intake-manifold leaks paled to insignificance.

[cadman56]

Let me jump in for just a sec.
Does you car have the vacuum operated air pump?  That one item can cause a great deal of issues regarding idle quality.  I finally had to disconnect mine until I was able to locate all the parts to rebuild it.  That was in the early 80s.  I don't think parts are available for those anymore.
Anyway, once I got my pump rebuilt  all idle problem disappeared.
And yes, I did go through everything mentioned above.

[E Masters]

Hi Mike and to all members. I'm Ed and new to the site.

I recently had the same issue and found a few issues with the carb.

The first being the little bypass seal at the back of the carb where it leans the mixture when hot. The tiny seal was cracked.

The second was the secondaries weren't seating properly on occasion.

The third and main issue was the metering rods position in the jets. The thin retainer wire holding the rods somehow moved and was not allowing the rods to fully go down with vacuum at idle. It was no more than one millimetre but made a difference. The rods were also not sitting at the correct depth in the jets. Somewhere in its history it had been altered.

It was difficult to find specs for correcting the rod height but luck has two diagrams in the workshop manual clearly showing the position.

Not only was the idle improved the acceleration up to the opening of the secondaries was also improved.

It changed the car. Hope it helps.

[www.eldorado-seville.com]

Yes Greg, the stainless shim is in place. I used a new high-temp composition gasket below and above the shim.

Only one gasket was used on the intake, then the shim and the carburetor.
https://www.eldorado-seville.com/files/blowngasket.php