News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

Quadrajet Idle Problem

Started by MikeLawson, April 14, 2020, 06:42:28 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

MikeLawson

There have been a number of recent posts about Quadrajet carburetors so I thought it might be a good time to bring up a problem I'm having the one on my '67.

I've had the car for a little over a year now and although it runs fine out on the road, the idle has always been somewhat rough. After many attempts at adjustment it would only idle best at around 750 RPM. Recently, I rebuilt it and I was very careful to clean out all the passages. I ran a wire through every opening, blew compressed air though them and shined a light through wherever possible to verify they were clear. I did not replace the idle tubes but I know for certain they were clear. I carefully followed the shop manual instructions and checked off each step as it was completed. The car only has 45,000 miles and the carburetor appeared to be in very good condition and was quite clean inside.

After reinstalling the carburetor on the car I pretty much have the exact same problem as before. I cannot get a smooth idle at 450 RPM no matter what.  At 750 RPM,I have a pretty steady vacuum reading of 20".  At about 600 RPM, the reading is 17"-18" with a rapid fluctuation of about 1/2 a point. I get the best vacuum reading with the idle screws turned out about 2 turns. The timing is set at 5 degrees advanced and the dwell is at 30.

I am at the point where I don't know what else to try and I'm looking for suggestions. Also, if it seems like it might be best to send the carburetor out for "professional help", I'm willing to spend the money to get it fixed rather than prolong the frustration. I'd certainly appreciate any recommendations for carburetor rebuilders on the east coast as I live in PA.

Thanks for any help or suggestions.


35-709

#1
You don't mention having done a thorough search for a vacuum leak.  You may already have, but --- just in case.
Block off every vacuum port on the engine and carburetor (if it sucks, block it, at the source), including the power brake booster (at the carburetor) and the hose/pipe to the transmission vacuum modulator, and block the vacuum port in the intake manifold.  Then run the engine, if it helps, start adding back one hose at a time until you find the leak.  Also, while everything is blocked off, check for vacuum leaks around the entire perimeter of the intake manifold --- the front and rear corners especially.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

35-709

#2
To add --- QJets also have a reputation for developing vacuum leaks at the primary throttle shaft, there is a kit to re-bush them.  I would expect this sort of problem in a carburetor with higher miles than yours but anything is possible at that age.  Use brake cleaner judiciously with a "straw" inserted in the nozzle to spray around the carb and intake manifold.  Warped base plates and air horns are also common from overtightening the fasteners (hoping to prevent vacuum & fuel leaks! ;D)
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

67_Eldo

I don't know which '67 you have but I have a '67 Eldorado. I just went through the same routine you described over the course of more that two years after having many things "rebuilt" for an astronomical sum.

Over time, I got the car to idle better -- but not perfectly -- by doing the following:

* Disconnected the whole Automatic Climate Control system. That is a snake pit of hoses and valves I did not want to mess with so I plugged it all off.
* Disconnected every other vacuum line that wasn't essential (e.g. parking-brake release, trunk release).
* Disconnected the headlight doors.
* Rebuilt the distributor, adding a new vacuum advance.
* Replaced all the hoses that are essential to operation (e.g. the hoses to the THM 425's vacuum modulator).

After all this, the car ran well but still idled in a way not befitting a Cadillac. I was sort of embarrassed last summer when, in the not-so-well-to-do part of town in which I live, a late-60s vintage Rolls Royce pulled up next to me at a stop light. He out-smoothed me at idle!

So I asked a friend who is a very good mechanic (and excellent body-shop fellow) for advice. He hosed down my carb with Gumout and said take a look at it again in a few days. Sure enough, even though my carb had been subjected to a megabuck (and I mean $1k +) "rebuild" two years ago, gas was seeping out of every seam. Obviously there were vacuum leaks. But there were even more non-carb issues.

He suggested that I change the plugs. Up until then I figured plugs would have nothing to do with it since the car had been subjected to more than $25k worth of work a mere two years earlier. I hadn't even put 5k miles on it since then. But I went ahead and pulled the plugs. Surprise! I found two different types of spark plugs, six Japanese plugs and two rusting old AC Delco plugs. The range of plug-tip coloration varied from dark grey to chalky white, and none indicated serious failures. Still, all that money and old plugs ... grrrr.

I also checked the radiator. There was a tiny bit of oily scum floating on top, but I thought that might have been left over from the flushing/de-rusting of the cooling system I performed last summer. I let the car idle for quite a while and eventually I saw some tiny, but dreaded, bubbles. Maybe I had a leaky head gasket or cracked head? On the 429, that's within the realm of possibility.

I drained the cooling system, bypassed the heater core, pulled the thermostat, and flushed it out with water a few times. Then I refilled with water + 1/2 bottle of K&W Fiberlock nanotechnology head sealant. After three days and 200 miles, I drained the system, filled it with water, and let it idle for quite a while again. Sure enough, bubbles were still there, but they were much smaller and there was no oily residue in sight. So I drained and refilled again, using the second half of my bottle of K&W. After another few days and 200 miles, I drained the system, hooked up the heater core, popped in a new 180-degree thermostat, added antifreeze, let it idle, and ... no bubbles! Yay! (Fingers crossed.)

By this time, the Eldorado was idling pretty well -- maybe Chevrolet well -- but still not Cadillac well. (The 429 is, after all, legendary for its smoothness.)
So I bit the bullet and plunked down $400 on a remanufactured carb. Using the number that was stamped on my original carb, the carb guy told me I had a 1969 QJ. He could send me either a '67 QJ that didn't match my carb number or he could send me a '69 carb that was a match for my number. I went with the number match (which is what he recommended as well).

When I removed my old carb, I noticed that there were carb gaskets on both sides of the stainless-steel shim. I called the carb guy and he said that some folks use two gaskets and some follow the original spec (carb -> stainless -> gasket -> manifold). Since they machined the bottom of the remanufactured carb flat, I decided to go with the manual recommendation and use only one gasket.

The new carb had its vacuum outlets located in slightly different positions as my old carb, but everything bolted right up. I bypassed the thermostatic vacuum control on the radiator and connected the carb's manifold vacuum out to the distributor advance in. I plugged the carb's ported vacuum outlet.

I didn't have a torque wrench handy at that moment, so I torqued the bolts and screws gently by hand to what I figured would be a safe degree that was probably less than the manual-specified torque.

The Eldorado fired up immediately and idled like a Cadillac! When I got it out on the Interstate, my built-in Bosch O2 sensor was reading a mixture of 14.4! Perfect! Fuel injection couldn't do better. I drove it for a day like that.

Then I tracked down my torque wrench and tightened everything to spec. The idle was still perfectly smooth but on the highway, the O2 sensor read out between 13.5 and 14.4. So my under-torquing of the bolts must have been allowing a tiny bit of air in around the carb base.

So now I'm done chasing the rough idle. If a leak in the head opens up again, that won't be fun. But until then, I'm OK.

I hope there was a helpful clue contained somewhere in that story. :-)

35-709

 :)  Good one!
And yes, check the plugs, whether you replace them or not, be sure the gap is correct.  Check the points for condition and the dwell AND, if we are this far with no good results, replace that d*mn condenser.  Cheap part and can cause weird problems.  Remember, as Greg Surfas might say ( :)), if you think it is the carburetor it will be ignition --- if you think it is ignition, it will be the carburetor.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

67_Eldo

I didn't have to worry about points because I have an Ignitor I.

Now I have to worry about keeping the ignition switch in the ACC position for too long! :-)

savemy67

Hello Mike,

I can't concur enough with Geoff's and Scott's posts.  There have been many posts on this forum re carburetors (or some other part) wherein the implicit expectation is that after the expenditure of a small fortune, said part should make the car run like it came off the showroom floor - even though the rest of the car is fifty years old.

Most engine components are dependent on each other.  A beautifully rebuilt carb will not resolve a vacuum leak in the climate control system, but that leak in the climate control system will affect the engine's ability to idle properly.  My suggestion is to take a holistic approach to your diagnosis.  This involves a broader understanding of how the components work together.  Sometimes this understanding can be gleaned from the service manual, and sometimes other sources and experience need to be found (this forum being a reasonably good resource).

A good question to ask a Q-jet rebuilder is, do they check the underside of the air horn and top of the fuel bowl for flatness?  Do they use a dial indicator to measure primary throttle shaft side play in two axes?  The point being is that a shop is only as good as the tools they use and the skill of the tool operator, so be sure to ask questions.  But you won't know what questions to ask until you become more versed in how things work as a system.

Scott's adventures should be instructive.  The fact that he uses an O2 sensor means he understands the importance of stoichiometric ratios (and he can optimize his fuel economy while avoiding too lean a mixture).

Here is an example of what might cause a rough idle that has nothing to do with the carburetor.  If two of your engine's eight cylinders have a compression test reading that is 12 percent lower than the other six cylinders, what happens?  Some of the compressed air/fuel charge in the combustion chamber escapes due to a defect in the rings or a valve.  The air/fuel charge will ignite, but the effect of the energy output will be somewhat less in the two cylinders that have lower compression.  This means that the two pistons in those cylinders will not be driven down with the same force as the other six cylinders, so the crankshaft will rotate somewhat slower.  In other words, a drop in engine RPM.  The carb may be perfect, but the air/fuel charge in the lower compression cylinders won't have the same energy content because the volume of the charge has decreased.

I wouldn't necessarily rebuild the engine to restore equal compression because I had a rough idle.  I might do a compression test and or a leak-down test to know how well the cylinders were sealing.  Then I would rebuild or adjust the carb for the best outcome given the condition of the cylinders.  Again, the engine works as a system.

I have a way to go before my '67 is ready for prime time.  My engine has 90,000 miles on it.  Is it perfect?  No.  Does it idle as it should based on the service manual?  No.  Can I live with it?  Yes, and it keeps me thinking about the next incremental improvement.

I live near Baltimore.  Where in PA are you?  My brother lives in Philadelphia, so I am in Philadelphia a few times a year.

Respectfully submitted,

Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

79 Eldorado

Quote from: MikeLawson on April 14, 2020, 06:42:28 PM
There have been a number of recent posts about Quadrajet carburetors so I thought it might be a good time to bring up a problem I'm having the one on my '67.

I've had the car for a little over a year now and although it runs fine out on the road, the idle has always been somewhat rough. After many attempts at adjustment it would only idle best at around 750 RPM. Recently, I rebuilt it and I was very careful to clean out all the passages. I ran a wire through every opening, blew compressed air though them and shined a light through wherever possible to verify they were clear. I did not replace the idle tubes but I know for certain they were clear. I carefully followed the shop manual instructions and checked off each step as it was completed. The car only has 45,000 miles and the carburetor appeared to be in very good condition and was quite clean inside.....

Thanks for any help or suggestions.

Mike,
I didn't see in your description if you did anything to the plugs on the bottom of the fuel bowl. They are visible when you remove the base plate. There is often a sponge in that area because they are known to leak. There are 4 positions which need to be checked. The sponge was there to catch leaking fuel but when a sponge eventually gets saturated it still drips. The book I read recommended filing them and resealing them.

I have better tools now than when I did mine. At the time I didn't leak check them but I suspect you probably could figure out a way to leak check them using a Mighty-Vac or similar. Seal the area from the top, switch to pressure and spray the plugs with soapy water like kids bubble blowing solution.

If you repair them just be careful that the repair doesn't stick out to the point where you can no longer assemble the base. I guess you don't need to ask me how I know.

I don't know if that could be an issue in your case but I thought I would mention it.

One other thing I just thought of which I wonder if it could cause something like you described would be float level set to a point where it was slightly over filling.

Scott

Cadman-iac

Those plugs on the bottom of the main body can be purchased through Napa,  and the replacements have a small spike or tooth, whatever you want to call it, that sticks down and rests against the base plate when it's installed.  This helps to keep them pressed in place. They also have an "0"ring seal on them for a more positive sealing.
If memory serves,  the part number is something like 2-88 and it's in their Echlin carburetor line. It's been some time since I last bought one, but I believe they are still available. It also has a small instruction sheet that comes with it.
HTH,
Rick
CLC# 32373
1956 Coupe Deville A/C car "Norma Jean"

MikeLawson

Thanks for all the advice so far.

Before I rebuilt the carburetor, I went through many of the steps which have been suggested here. I'm going to systematically repeat the process in hopes that I missed something the first time or possibly a replacement part I installed was actually bad. As suggested, I did run the engine with all the vacuum lines disconnected and it did not change. I checked the compression and all the cylinders were at 180-185 psi. I checked the vacuum advance unit and it functions properly. When I rebuilt the carburetor, I installed the repair plugs mentioned above. The current spark plugs are AC44 which may have been installed a long time ago but they showed little signs of wear and appeared to be firing normally. I glass beaded, regapped and reinstalled them. I now have a new set of AC43S plugs on order which I'm going to try. When I first started working on the engine, the air filter, distributor cap and rotor looked in very rough shape but replacing them had no effect. It sure would be nice to find the "smoking gun".

MaR

My 50k mile Q-jet had a leaking, rough idle issue before and after a rebuild. I took the air horn off of it again and checked it for flatness and it was warped by about .070". After reading extensively about the subject of warped airhorns, I just decided to use to old school route of using two airhorn gaskets and that seems to have fixed the issue.

67_Eldo

As far as vacuum connections go, there are many that can be easily overlooked.

I replaced the hose and the check valve going to the power brakes.
I replaced the PCV and the vacuum hose running to it.
The rubber-attachment ends of the pipe that carries vacuum to the transmission.
Any vacuum canister for options like door locks can leak.

Its quite an Easter-Egg hunt!

Jeff Rosansky CLC #28373

Quote from: 67_Eldo on April 15, 2020, 08:45:54 AM
Its quite an Easter-Egg hunt!
Believe me, I know. Have been chasing it for years.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

klinebau

Quote from: MikeLawson on April 14, 2020, 06:42:28 PM
I did not replace the idle tubes but I know for certain they were clear.

The restriction in the idle tubes is only at the very bottom of the tube.  It is best to remove the idle tubes to clean them out and to make sure that the area underneath the idle tubes is free of build-up/debris.  If this is not possible, you can insert a long fine wire (welding wire would work) to clean the ends of the idle tubes.  You need to make sure that the engine is getting enough idle fuel. 

Checking for vacuum leaks will be the next most important area.  Vacuum leaks through the primary throttle shaft are possible, but with a carb with so few miles, this would not be high on my list. 

If you were to rebuild the carburetor completely, I would do the following: 

1.  Remove and clean the idle tubes.  You can replace and re-drill them if needed.
2.  Re-bush the primary throttle shaft
3.  Remove and replace the fuel well plugs with threaded inserts
4.  Use all new ethanol-safe parts (float, needle/seat, accelerator pump)
1970 Cadillac Deville Convertible
Detroit, MI

67_Eldo

As far as carb rebuilding goes, in addition to my own QJ struggles of many years ago, my Eldorado's carb was rebuilt by full-time mechanics two years ago. I figured that if they couldn't do an adequate job, given all the tools and umlimited funds (!) they had at their disposal, the odds of my success were pretty low.

Nonetheless I did lots of reading. If I were to rebuild my own carb now, in addition to the steps mentioned above, I would:

* take the main sections of the carb to a machine shop and have all of the mating surfaces trued up.
* have the completely disassembled body boiled for at least a day. (My old carb, which was full of varnish, was boiled for a week.)
* in addition to new throttle-shaft bushings and fuel-well plugs, I'd place a layer of epoxy over those once they were fitted.
* I'd try to figure out how to line the entire inside of the fuel bowl with epoxy to make double sure it is all sealed. (There's a QJ rebuild place in TX that claims to do all this. But their lead time at the moment is 11 weeks.)

After thinking about all the running around I'd do in the process of performing the above steps, I figured it was better to simply buy a carb that had been massaged by folks who do nothing but carbs. The only thing not done to the carb I received is the line-the-bowls-with-epoxy step.

BTW, QJ casings were thicker in post-1974 models to minimize warpage.

67_Eldo

Another interesting step that the TX carb people take is to re-jet the QJ. The difference in gas quality between the 1960s and now, in their opinion, merits rod and jetting changes.

The place I got my carb from, however, sticks to the original specs. Their claim is (as we've heard in this forum on occasion) Cadillac knew better than anyone how to jet the QJ. Don't mess with it.

"Cadillac Kid" Greg Surfas 15364

Mike,
Just a thought here. Your car should have a switch pitch transmission that allows the converter to go to high stall speed when stopped at idle in gear WITH YOUR FOOT ON THE BRAKE. I am assuming you are setting the idle speed with the car in gear following the FSM's instructions. 
I might suggest trying to set the idle with someone in the car holding their foot on the brakes, assuming your switch pitch is functional this might improve your results.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

TJ Hopland

One tip I would like to add that isn't likely the problem here but I'm sure others with their own issues will be reading this thread in the future is something I have seen more recently with replacement floats. 

I don't know what the official name or material is but in the float area there is a non metallic plug that fits in before you put the top on.   It sits over the float arms and I have now seen it more than once where the arms on the new float will hit this plug before the needle actually seats. 

You almost need a few more hands and fingers to hold it all together and flip it upside down to check it but you really need to make sure that when the needle is seated there is still some clearance between the arms and the plug.  My fix was to take a file or dremel sort of tool and grind a little out of the plug to clear.  It doesn't take much to clear but on the ones I have seen it wasn't hitting by much either just enough to cause the needle not to seat when it was supposed to.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

MikeLawson

Quote from: "Cadillac Kid"  Greg Surfas 15364 on April 15, 2020, 01:06:53 PM
Mike,
Just a thought here. Your car should have a switch pitch transmission that allows the converter to go to high stall speed when stopped at idle in gear WITH YOUR FOOT ON THE BRAKE. I am assuming you are setting the idle speed with the car in gear following the FSM's instructions. 
I might suggest trying to set the idle with someone in the car holding their foot on the brakes, assuming your switch pitch is functional this might improve your results.
Greg Surfas

Greg,
I did make the idle adjustments with the car in Drive.  I pretty much followed the procedure in the 1967 Shop Manual and there is no mention of the need to apply the brake. When I reinstalled the carburetor, I readjusted the transmission switch according to the procedure in the manual. I also checked the operation of the switch by turning the ignition on and pulling back on the throttle. With the throttle just slightly off idle, I heard a click in the transmission as the switch pitch solenoid operated. As I pulled the throttle back further, I heard a second click which was the down shift solenoid operating. As far as I can tell, the brake pedal does not need to be pressed down for this to happen.

I have another question regarding the preferred spark plugs for this engine. The originals were AC44 which have discontinued for a long time. The current AC catalog specifies R43S plugs and a 1990 AC catalog I have specified R45S plugs. I looked through my parts stash and I have R43S, R44S and R45S plugs on hand. Because the R44S plugs are also discontinued, I can't find anything that tells me if they are the same heat range as the original R44 plugs. Of these three choices is there one that is "just right"?

I have some new tune up parts coming from RockAuto and once I get them installed, I'll report back with the results.

fishnjim

Just consider, it's only necessary to idle at that speed to set the timing correctly.   The earlier procedures it was 450 in "drive" - so foot had to be on brake - but I don't recall specifics for '67 procedure.  I put a tach inside for ease to monitoring.   Dwell/tech meter is handy.   
I rebuild '67 rochester years ago with no issues, but how they are today with newer parts, gas, etc is a subject unto itself.  You don't get everything in the rebuild kit that maybe needed.   Check for worn parts.   I agree rejetting maybe necessary at WOT if it's running lean.  The plugs will show this.   But you'll need a exhaust gas analyzer or bench/test stand/motor (carb shop equipment) to tweek it.   Ethanol is less combustion energy, so less "fuel" in fuel/air.   But only 10% or so.
600-750 rpm is not necessarily an "idle" issue, rough is a different story, if that's where you car wants to run now in park barring other issues.   I doubt it's in perfect order everywhere.
Any idle up system has to be disconnected when tuning it.   Plug the advance holes.   A  rubber plug and golf tee is standard '60s tune-up equipment.
Generally speaking, "rough" idle is instant vacuum leak territory with carbs.  Air influx messes with the idle circuit.