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

67 deville quadrajet problem

Started by Julien Abrahams, September 01, 2018, 02:55:52 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Julien Abrahams

Hry guys, and update on the vacuum leak topic earlier.
So, last week I cleaned the fuel filter,  which was slightly dirty some very minor debris. Took apart the carb to check the gaskets. They were/are fine. Put everything back together let it sit for a week.
Started the car today, after 2 seconds of cranking, the fuel filter was almost full. After the fuel bowl of the carb had filled (second time cranking for about 3 seconds) the engine fired up and ran OK. Took it for a short drive around the block to let it somewhat warm up. Then opened the hood, took off the air cleaner and checked the choke vavle (if it was working correctly). That was fine. It was about 3/4 open. Manually set it to base idle. Engine ran smooth. Closing the choke valve by hand made the engine run worse. Nothing out of the ordinary.  :(. I had not really changed anything and now it was idling just fine. Went grocery shopping. Car ran fine. After coming back started the car, and slowly but surely the bad idling symptom returned. What the...? Took it home, idling got worse.
I spent about an hour to look for vacuum leaks uring a propane torch and brake cleaner. I found none. No matter how much i tried, the engine RPM would not change. A shot of brake cleaner down the passengers side of the primary side of the carb had an immediate effect (engine rpm rise). Doing the same on th driver's side made the rpm drop. I got the same effect whith drops of gasoline (from a bottle). It has the symptoms of a vacuum leak, but the are none. Could there be an internal carb leak while the gaskets are good? This one has me stumped. Help isverymuch appreciated.

1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

savemy67

Hello Julien,

One of the talked about problems with the Q-jet is the fact that the airhorn can get warped by over-tightening the two front mounting bolts.  When I recently rebuilt my Q-jet, the air horn was warped.  If the airhorn is warped more than the fuel bowl, it is possible to get an internal air leak which could affect idle.  In my case, my fuel bowl was warped in the same way as the airhorn, so I got a good seal.

Photo 5063 shows to top of the fuel bowl.  Notice the very fine raised lines around the passages.  These lines are part of the fuel bowl casting and they help seal the passages when the gasket is sandwiched between the the top of the fuel bowl and the underside of the airhorn.  Photo 5062 shows the gasket that is between the fuel bowl and the airhorn.  Notice the indentations in the gasket that are formed by the raised fuel bowl casting lines when the gasket is clamped between the fuel bowl and the airhorn.

When you took apart your carb, did you place a straightedge across the bottom of the airhorn and top of the fuel bowl?  Did you notice if the fine casting lines on the top of the fuel bowl were present?  Did the gasket show the indentations of the fine casting lines completely around every passage?

Another issue I had with my Q-jet was very worn primary throttle shaft holes in the throttle body.  I rebushed them and all the play in the shaft was eliminated.  If you have very worn primary throttle holes, it is possible to get a vacuum leak at this point.

From your post, I am not sure how precise you were when adding fuel to the primary bores.  If you did not add a measured amount, I would repeat that test using a measured amount in both primaries to see if you get the same result - one primary RPMs increase, the other primary RPMs decrease.  What is the condition of the taper on both of the idle mixture screws?  What is the number of your carb?

Respectfully submitted,

Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

Julien Abrahams

Christopher, thank you for your reply. With regard to the fuel bowl/air horn gasket, i did not check that yet. With regard to adding fuel to either primary bore: the bottle I used has a very small tip which results in a steady "flow" of fuel (drops). I repeatedthe test about half a dozen times on each of the primary bores and I got a rpm rise with drops of fuelon the passengers side ajnd a drop in rpm woth drops of fuel added to the drivers side.
The weirdest part is that it idled fine for about an hour. Maybe something settles after being fully warmed up.
Today i will take the carg off, dismantle it and look for problems.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

Julien Abrahams

So, i took the carb off and apart yesterday. I think like most quadrajets mine is also warped slightly. Both the airhorn and float bowl appear to be warped the same but I find it hard to tell. Checked the airhorn to float bowl gasket. The indentations were even and all around. All passageswere clear. Float bowl-airhorn and throttle body-flost bowl gaskets were good. Carb to intake gasket is good.
Only thing i noticed was one screw of the airhorn to float bowl was slightly loose. This was on the troublesome side. In the attached oicture this was screw nr 4. Ther was some sort of small bracket that was held on with the same screw. The bracket does not appear to have a function and i don't see it in any of the online pictures of a quadrajet 4 mv. The bracket would be across/ on top of the secondary air valve lockout tab. As to me it appeared to serve no purpose, i removed it and tightened the airhorn screws in the required sequence as evenly as I could being carefull not to over tighten them.
Have not been able to take the car for a testdrive yet....
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

"Cadillac Kid" Greg Surfas 15364

Julien,
I believe the "bracket" you are referring to is the choke linkage guard.  If so and if there was something binding in the choke linkage or choke pull-off linkage that might contribute to the problem.
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

Are you doing this recent work with the carb still mounted on the intake or have you been pulling it off?

Does the 67 have the open exhaust crossover port in the carb base?   Apparently getting a good modern gasket to properly seal there can be tricky.  Even with a good gasket a stuck EFE valve can burn it out in a fairly short period of time.  A leak there is like having a stuck open EGR.  Would also fit only effecting one side and not being able to find an external leak. 
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

savemy67

Hello Julien,

In attached photo 5044, I am using a straightedge against the underside of the airhorn to see if it is warped (it is).

Photo 5070 shows my intake with the gasket in place.  The gasket is made to accommodate the exhaust crossover passage in the manifold.  A stainless steel shim goes on top of the gasket and underneath the carb.  The shim covers the crossover openings in the gasket.

Photo 5038 shows the throttle body (base) of the carb.  You can see the top of my workbench through the opening in the casting ahead of the primary throttle bore.  This opening is closed off by the shim.  Not visible is a notch on the side of the primary throttle bore below the throttle plate closed position.  The notch allows manifold vacuum for the distributor advance, the PCV system, and the choke pull-off.

Photo 5069 shows the carb from the choke side.  The choke rod comes up through the airhorn and engages the choke valve bellcrank (the green part).  There is an arm on the bellcrank, just to the left of the rod, that engages the secondary air valve lock-out lever (the curved part to the left of the bellcrank arm).

My carburetor did not have anything secured by any of the 9 airhorn attaching screws.  My carb number is 7027231 which is correct for my '67 Sedan DeVille.

Respectfully submitted,

Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

Julien Abrahams

Update:
Thanks for the replies guys.
So a couple of days ago I took the carb off and took it apart ( see my previous post). After hitting the accelerator to set the choke i noticed I wasn't hearing the usual clicks from the transmission. Turned out that the transmission downshift switch had broken (the plastic bit that connects to the carb). Bummer.... Add to "to do" list...Epoxy glue?
Took the car for a drive. After it had warmed up I noticed base idle was much higher than before. Remembered that in my quest to discover the causeof the bad running I also had checked to see if changing the timing had an effect (by rotating the distributor slightly) and I sanded the contactpoints. So, checkd the timing which was at about 6 degress btdc. Shop manual states 5, but i left it where it is because engine was running well. Also checked dwell angle which had changed quite dramatically from 31 to 15 degrees. Adjusted  that back to factory spec (30 degrees). Idle speed dropped somewhat. Then adjusted idle speed at the carb. Becuase I had removed the mixture screws, I reset the idle mixture by turning the mixture screws one at a time to obtain the highest idle. Finally set the idle speed with the adjustement screw so it idled around 650 rpm in Park. Now it runs very well, idling is very regular.
Now I only need to fix the transmission downshift switch, hopefully by glueing it back together using epoxy. This switch not only controls the downshift but also the switch pitch in the trnamsission which, i found out, makes a difference in power delivery.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

klinebau

Changing the dwell will affect the timing.  You need to re-adjust the timing after adjusting the dwell.
1970 Cadillac Deville Convertible
Detroit, MI

"Cadillac Kid" Greg Surfas 15364

Julien,
The '67 had a unique switch that not only controlled the transmission kick down it also controls the switch pitch stator.  Ut is a rotary switch whose shaft fits into the side of the carburetor linkage.  Is this the switch you have or has someone installed a different switch?  If so, you may not be engaging (through change of the wiring circuit)( the switch pitch stator which will substantially effect your "in gear" idle performance.
Here is what the 1967 (ONLY) switch looks like.
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-

Julien Abrahams

@ Greg: yes, that is exactly the switch. And the little (plastic?) square that you see in tne first picture is what broke. So, hopefully i will be able to fix it by glueing it back together.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

DeVille68

Quote from: Julien Abrahams on September 04, 2018, 02:55:18 PM
@ Greg: yes, that is exactly the switch. And the little (plastic?) square that you see in tne first picture is what broke. So, hopefully i will be able to fix it by glueing it back together.

Yes, mine broke too. I repaired buy using a rectangular plastic piece and I drilled two small holes into the two plastic pieces. Glued a metal nail into the holes, such that my "construction" can support the twisting motion. Only glue may not be strong enough.

Best regards,
Nicolas
1968 Cadillac DeVille Convertible (silver pine green)

fishnjim

I hope you've solved your problem but I don't think so. 
Troubleshoot 101: An intermittent problem, needs to be addressed/solved by things that occur intermittently.   Loss of power/speed is mostly caused by fuel or spark issues, if the cylinders are functioning.   Fuel has to be the right amount for the rpms and in the right air ratio to idle smoothly.   Vacuum is variable and a resultant function of the rpm affecting air ratio mostly, but some items function off it.
Rochesters, were pretty good by '67, but being that old, you really need to tear them down and thoroughly clean/check them and put fresh parts in to be sure the carb is right.   Who know what's been done or not done to it and would really admit it?   I don't put much faith in the horns being off doing that much here as that would cause a steady issue.   
Could be just out of adjustment but that's more a steady problem and can only be intermittent during periods of being out of adjustment.   One has to go around several times when adjusting these carb/points cars til you get to steady baseline idle rpm and timing/dwell.  Then leave it alone.   
These days, one has to contend with fuel they weren't designed for, so I sometimes recommend a tailgas analyzer be used to adjust carbs with ethanol fuels over traditional methods eg; may need a jet size change but that's not evident here or switch to higher octane non.
Might also be prone to vaporlock, that's an intermittent type problem and you've already had problems there with the fuel bowl not filling.   I'd be focused around the fuel delivery system much more as a prime suspect.
If concerned about the non-functioning switch, a steady issue, I'd see if I could find a good part, substitute or way to eliminate from circuit before I'd trust a glue job and add uncertainty/complexity.   Switch malfunction may cause intermittent problems in some other function, but need to study the circuit diagram for that.   Most likely it's either on or off, and those are steady things except for the transition.
I like fuel, vacuum, and rpm gauges added on these cars, it helps with understanding what's what, even if you're familiar.

67_Eldo

#13
My 67 Eldorado also had the broken carb-switch problem. Although I found a NOS switch to replace it, the price was $500 for the switch. I let that "opportunity" slide by.

I now use Bruce Roe's switch-pitch control box in place of the original switch-pitch set of contacts and an aftermarket kick-down switch for the kick-down contacts. The control box and kick-down switch work fine together, but they aren't original.

Someday I'm going to open up the original switch and see if I can 3D print some replacement pieces. But the problem is that the switch's neighborhood gets *mighty* hot. Too hot for most 3D-printable plastics and maybe even too hot for glued parts. I'm sure the extreme heat those switches are subjected to is a huge contributor to their typically short lifespans.

BTW, this may be an Eldorado-exclusive thing but how does everyone access the passenger-side fast-idle-jet screw? On my car, the rear compressor bracket makes it impossible to access, even with the suggested gooseneck tool. If that bracket had a small access hole through it, life would be easy. But as it stands, I can only get a small needle-nosed pliers onto the jet screw (from the side) and turn it about 1/128th of a revolution with each twist. Any nifty tools or tricks to get in there more effectively?