472 started but can't get idle rpms down

[TJ Hopland]

Can you feel any slop in the throttle shafts?    If there is that may explain some of the weirdness.  IF the bores are worn the throttle shafts could be moving all over the place and changing the spacing and also being inconsistent where they land each time.   Checking those can be tricky kinda like checking balljoints.   Its hard to get a good read on them due to the spring tension. 

[rms70]

Bump

["Cadillac Kid" Greg Surfas 15364]

Rob,
In your first post you mentioned that the carb had been "worked on" by someone other than yourself of unknown skills as it comes to the Quadrajet.  You seem to be chasing gremlins and they all seem to be hiding in the carburetor.  Perhaps biting the bullet and having someone who is knowledgeable rebuild the carb.  It is very possible to damage these carbs by incorrect assembly.
Greg Surfas

[rms70]

I moved the post up today so Scot M could find it.  He lives near me so I hope this is the beginning of the end....At least for this issue.

                                                .                            Rob

[chrisntam]

Send him a pm or do a new post and title it "CALLING SCOT MINESINGER".  He usually answers.

[Scot Minesinger]

Yes, read thru this now.  Have re-built several Q-jets using Daytona parts and it works well.  Rob did PM me so we can get this done.  Drove to KY GN 2019 and back on my rebuild, no problem ascending those 7% grades for 5 miles blowing past those mini vans at 80 mph on rt 64.

[70DeVille]

 If you push back on the throttle on the carburetor while the engine is racing and the RPM's lower, you definitely have a bad THROTTLE BODY in the carburetor.

This is a common problem even with rebuilt carbs since most rebuilders don't attend to the throttle body, they use your old one. Of the four dozen '68, '69 and '70's I've owned, a number of them have had this problem. You need to tell the rebuilder to check the throttle body.

[70DeVille]

Would love a response to my solution suggestion.

["Cadillac Kid" Greg Surfas 15364]

Michael
Dirt, misfit linkages, incorrect assembly of many components, as well as sticking internal parts will result in similar symptoms. Someone versed in these carburetors should determine EXACTLY what is occurring IF the problem is in the carb itself before they start throwing parts at it. If this were me the first thing I would do is to disassemble the choke/fast idle linkage and components and reassemble them correctly then set the fast idle and see what the results are
Greg Surfas

[70DeVille]

Greg,
Pushing back on the throttle doesn't require any disassembly. It's the least invasive, easiest test. It is a very common problem with old quadrajets.
Michael

[rms70]

Thanks to all who have replied and please understand the things which made this a 2 decades project still keep me from getting things done on the car.  I don't know if another rebuild or a swapped rebuilt carb will be needed, I don't recall any driveability or performance issues when last driven, only leaking exhaust-manifold gaskets were the problem for state inspection.  The problem I'm seeing is once started and the vacuum break unit has begun to open the  choke i should see(according to the Delco carb manual) "at the same time the fast idle cam follower lever on the end of the primary throttle shaft will drop from the highest step on the fast idle cam to a lower step when the throttle is open."  My fast idle cam and the cam follower will not just slide against each other , it's  even sticker  if I move fast idle screw in to it's "bench" setting 1600 rpm. If screwed out to a light drag between cam and cam follower then  rpms are too low to start. Further out so fast idle cam is just supported by tang on vacuum break lever and not enough rpms for start since throttle lever is sitting on low idle screw.  What force is normally breaking the tension on the cam and follower?  Is the follower supposed to be moved out of the way as it does when you step on the throttle(it pivots back to allow fast idle cam to go to cold start position)? Don't know if the pictures will help but one of them shows the screwdriver blade pointing at the cam and cam follower intersection with the fi cam in cold start position. The other is after that fi cam has dropped. And don't ask me why or when my intake manifold was painted red.I'll just promise that it"s a 70 Deville.

                                                                              Rob

["Cadillac Kid" Greg Surfas 15364]

Rob,
Something does not look right. I've attached a couple of shots of a correct 70 carb.
Greg Surfas

[rms70]

I'm not at car now but the next step should probably be to pull out the carb so better /more equal views can be the seen.  BTW your carb  looks great, especially the throttle body plate.

                                                                        Rob

["Cadillac Kid" Greg Surfas 15364]

Fully rebuilt and set up for 10% Ethanol. If it is something you might find yourself interested in PM me
Greg Surfas

[klinebau]

I see that you have removed choke from the "stove" in the manifold.  If you are attempting to test the choke lever, you might as well remove the choke rod from the lever.  It will be easier to test this way. 

The fast idle cam works this way:

1.  On a cold engine the choke rod pushes the choke lever up.  The choke lever has a tang which moves the fast idle cam up to the top step.  The primary throttle blades must be opened up for the choke to push up the choke lever because the cam follower puts pressure on the stops of the fast idle cam.
2.  When the engine starts and begins producing vacuum, the choke pull-off sucks in the air valve linkage rod and opens the choke slightly.
3.  As the engine warms up, the choke spring begins to relax and the rod pulls the choke open.
4.  When the throttle blades are opened (by pressing the gas pedal), the cam follower pressure is removed from the fast idle cam.  The fast idle cam will drop down to the next step by gravity if the choke is opened enough.
5.  Eventually the choke is fully opened and the fast idle cam drops all the way down.  At this point, the car will be at low idle.

[rms70]

This is my carb. One picture I hope shows fast idle cam up after throttle vacuum break lever has dropped. It's held up by tension from  idle follower. If I understand klinebau's post then I must tap throttle or gas pedal to remove this tension at each cold start as a normal procedure and nothing is really wrong with my carb. The idle follower does pull back when throttle is moved, I just assumed somehow this would happen without driver input.

                                            Rob

[rms70]

Here's the picture

[35-709]

Engines with modern fuel injection systems will slow down on their own as they warm, but our antique carburetors require a little more operator input.  If your RPM goes down to normal idle when you tap the gas pedal as the car warms up, then it does indeed sound like it is operating properly.

[TJ Hopland]

Many of the last set of pictures are fuzzy if you try to get them to full size to look for details but looking at that terrible paint job (on something that was never supposed to be painted) you have to wonder if there is paint in some of the linkages causing issues.  I tried to tell for sure but too fuzzy to see how deep the paint got.   

It also kinda looks like the heads of the screws may be chewed up.  That along with the bad incorrect on every level paint job just points to abuse in the past.  Someone that really knows these carbs needs to look at it in person and will likely be able to spot what is likely more than one problem in a few seconds. 

[DeVille68]

Hello Schwartz

Look at the last picture you posted. you see the (vertical) tang that makes contact with the secondary lock out lever. This sets your limit for the choke plate. Not look below that tang, you see another one (horizontal tang) which goes trough the choke mounting plate and goes below the high idle cam.
Bend this tang down a bit, because this tang limits how far the cam will drop when you "blipp" the throttle.

Also check and see if you have a damping device on the side of the carb in front of the throttle. In front of the throttle there should be a unit with a housing and a pin with a spring at the end. It makes contact with the throttle and prevents the throttle to shut hard and stalling the engine. On my car this device was miss aligned and prevented the throttle to move quick enough to be able to step down one step from the fast idle cam.

Let me know if you understand what I mean.

Best regards,
Nicolas