Ok, cannot get the Quadrajet 7042250 I just installed to idle correctly on the choke circuit.

I set the electric choke and fast idle cam per the manual, but it will not idle high upon initial start up. The fast idle cam is in the top notch but I am lucky if it will start much less idle past 600 rpm vs the 1500 rpm or so it should be at.

Can I advance the timing to help with this issue? Need some recommendations on where to go from here as I am grasping at straws at the moment. I have never had this happen, usually the choke works fine and any issues that may happen occur after the carb comes off the choke circuit.

Thoughts?

d1

 

there is a separate idle screw for the choke speed just below the hi idle cam(pass side),screw with spring around it,have you tried adjusting it?

 

Yes, I adjusted the screw to past the point where the fast idle cam could even engage the lever where it is supposed to rest on. It just won't idle high like it is supposed to...

 

Check for bent linkage, particularly the the throttle cam. I bent mine on a Quadrajet and the fast idle no longer engaged.

 

Verify the choke butterfly operating as it should when the engine is cold.
If the choke plate is closing off, then the linkage should be moving so that the fast idle cam is sitting on the screw. If it is not, then the linkage may be bent as stated above.

You said it was a carb that you just installed.What's its history?

 

All the parts are brand new on this rebuilt/reconditioned carb.

The fast idle cam and guide/follower are not bent and work in conjunction as they should. As I related in an earlier post, by use of the screw I overadjusted the cam so it went past the point where the guide notches could engage, hoping to see something different happen. But no major changes to RPM.

It should be noted the carb works fine when applying the throttle, but the choke idle has got me stumped.

d1

 

I dont have my Q jet book in front of me but does this 250 Q Jet have the plastic cam on the choke side? In other words is this a divorced choke 250? Divorced means the choke is separate and not directly attached to the carb. If it does have the plastic cam on the passenger side I have seen those slip on the shaft and or break/split from age/heat. Before you start over tweaking this carb please give us its application to zero in on what exactly you have (engine size, divorced or integral choke, stock intake, any other modifications? More info is better then less) As you may or may not know there are settings on both sides of this carb which need your attention.

 

The carb was purchased from CarbDocter. It has an electric choke and it works like it should when power is applied.

The fast idle cam has been overadjusted thinking I needed more "throttle" to get higher rpm. If I adjust the screw the opposite way it doesn't allow the "high idle" notch of the guide to engage fast idle cam....

d1

 

With the engine idling, did you put the fast idle screw on the specified step of the fast idle cam (passenger side of the carb) and turn the fast idle screw to obtain the 1500 rpm? After that, if the choke is closing and opening the carb enough to put the fast idle screw on the fast idle cam, you should have 1500 rpm.


I'll stick with the factory set up. As long as the hot air tubes are open and not leaking, the choke works perfectly.

 

No plastic pieces on this carb (other than the choke insert and choke pull off canister).

It is not a divorced choke and is directly attached to the carb. This model uses the choke pull-off system to adjust the fast idle cam.

And I am familar with the curb idle setting screw on the driver's side of the carb. But haven't messed with that as it is not the problem at the moment.

It is on a Edelbrock 3711 intake, which is sitting on a SBO 350.

I have gone full circle with carburetors. Started with a 1979 Q-jet and failed miserably with it (as others on the site indicated would happen) and that was after Cliff Ruggles recommended it and sold me a bunch of parts to modify it. Then went with an Edelbrock 1406, which did well and was easy to work on. Then went with a Holley which ran way to rich; even with adjustments I was burning through way to much fuel. And now to this 1972 Qjet.

d1

 

I guess that is what I am trying to convey. The adjustments you indicate above make no difference to how the car idles. Well it may make the engine die, but by no means does the rpm ever increase...

 

Well, that sounds as if the choke linkage/fast idle cam is not being moved into proper position when the choke butterfly is closed. When the choke is closed, the throttle must be opened fully to "set" the choke fast idle cam on the screw. Does the fast idle cam move when the choke butterfly moves open and closed?

I'm sure you know this, but I just want to walk through the operation to see if we can pinpoint where the breakdown is.

If the screw is contacting the fast idle cam, then turning the screw in will move the cam and move the primary throttle blades. Is that happening or not?

 

Fun71 beat me to the punch. With the car running and the fast idle screw on the step of the cam, turning it in opens the throttle, just like pushing down the gas pedal. If that isn't happening, then something on the linkage is missing or broken.

 

Maybe a picture would help us. I was having problems with mine but it turned out the electric choke was not working. But even when it was not working I could idle up the engine with the fast idle screw. It just stayed high. I had to climb on the motor but was able to see the screw touching the fast idle cam.

 

Yes, by turning the screw contacting the fast idle cam it moves the throttle blades. I actually turned the screw in fully hoping to see something different idle wise and it may have increased 200 rpm at most. But still not where it needs to be, plus by doing that it rendered the fast idle cam guide (3 notches) useless.

As mentioned in the answer above, it slightly increases the RPM when I max out the screw. I will have to figure out what linkage is missing or broken....
-------------
And I will get some pics posted of the carb tomorrow night.

Thanks for the replies everyone.

d1

 

Hmm. Perhaps there is something going on and your curb idle setting is way too high, so there isn't anything left for the choke fast idle screw? Just throwing out ideas here.

 

If your high idle screw pushes against the fast idle cam properly, and causes the throttle plates to open properly, then it is working fine (perhaps / perhaps not in perfect adjustment, but working).

Time to check for vacuum leaks.

- Eric

 

Eric,
do you have a diagram of respective ports I should be pulling vaccum from on a q jet? I don't recall my other qjet having a choke pull off as I remember it being mechanical. Maybe I have my vacuum hoses attached incorrectly???

d1

 

There is a lot of variation in the nitpicking details of these carbs, and there's always the chance that pieces can be mixed and matched, so I don't feel comfortable saying anything specific about this or that port.

What would probably be best would be if you could post a few pictures of your carb., and then I or someone else here can tell you what should go where.

- Eric

 

X2 on this. I've seen far too many of these "rebuilt" carbs that were frankencarbs cobbled from parts that may or may not be designed to work together. I was looking at a 1966 Cutlass last weekend that had what at first glance appeared to be a correct 1966 Qjet with divorced choke. Once the air cleaner was off, however, it was clear that this was a pieced together rebuild. The stamped number on the fuel bowl casting showed it to be a 1972 Pontiac part, which did NOT come with a divorced choke originally. Actually, I should have caught that even with the air cleaner on, since the 1966 Olds Qjets used a side inlet like the Chevy carbs, and this one was a front inlet like later Olds carbs. Who knows where the rest of the parts came from.

 

I would contact Cliff again. Describe your problem and send him (and us) some clear pictures of both sides of the carb. Something doesnt jive here. Im with Joe on the Frankencarb. Tough to TBL shoot on line.

 

This isnt a frankencarb and I think I am done with Cliff's advice for the foreseeable future. Spent a lot of money on a late 70s carb with APT that did not work with my application, no matter how many of Cliff's adjustments I made to it (its documented at length in one of my other posts).
But I digress, I will get pics posted tonight after work.

 

Photo time.
It is entirely possible that incorrect pieces are in there, ESPECIALLY if "just redone".

One good way to observe the choke and Fast Idle action is to prop the throttle open so it releases the choke components, then manually move the choke plate and/or weight on the choke FI section and watch how the pieces move and interact. Speed screw contacts the FI cam on the proper steps, etc.

Every QJet has a choke pulloff as far as I know, but anything that might do, including being missing, should not result in what I hear described.

If the speed screw is moving the throttle plates but no RPM difference results, then the FI system is not the problem. Look into advancing the timing. Did you try a vacuum reading, see what that indicates?

 

Now you're talking my language, Chris.

- Eric

 

As requested

 

more pics

 

That looks like a QJ set up the way they were in the late sixties.

I see nothing out of place and everything looks like it's connected properly - it all looks right to me.

That being said, I cannot see the interplay between the fast idle cam, fast idle screw, and choke pull-off at all.

Have you checked for vacuum leaks?

- Eric

 

I will get a better picture tomorrow of the fast idle cam setup tomorrow.

Haven't had a chance to check for vacuum leaks.
Engine won't stay running long enough to effectively check for leaks, I have to constantly manipulate the throttle to keep it running. I guess I could wire the throttle lever open to allow me to check for leaks easier.

I will try again in the morning.

d1

 

I'm no expert but usually the problem is the last thing changed. While cold take a video of the carb linkage when you move the throttle and post it for us to see. If you change advance be sure to note the current setting so you can set it back. Don't want to get too much out of whack. Good luck

 

Maybe you should turn the idle mixture screws out more and see if that helps. Most people say start at 2 turns but mine needed 6.

 

Maybe it's just the camera angle but it looks as if the curb idle screw is turned in almost all the way. If so, you may be off the idle circuit and into the primaries and there may not be anything left for the choke fast idle. Maybe there's an idle issue that you had to overcome by turning the curb idle up more than it should be?

 

Aye, rowdy cam and retarded ignition can lead one to force the throttle plates open with the curb idle screw to get enough air in to maintain idle. When on Fast Idle, the curb idle screw should not be touching the adjacent movable part of the primary shaft fitting. To get it to stay running at an elevated idle [edit- FOR SERVICE], I have had luck placing a flat blade screwdriver in between the curb idle screw and the mating adjacent movable part.

Some ways around this are drilling holes in the primary throttle plates- even some factory carbs came this way- and drilling out the idle air bypass passages as set forth in the various QJet books.

 

Okay I really hate carburetors...

Here is what I have done with no change in low rpm in the fast idle circuit:

-Verified the fast idle cam guide (piece with the notches) actuates correctly and hit all "steps" in progression

-I ensured the curb idle screw was not affecting the fast idle cam

-I adjusted the idle mixtures screws to 1 3/4, 3, 4, and 6 turns respectively and it did not help

-I advanced the timing with no major impact to the RPM

-I isolated the carb from all vacuum sources (capped off the ports) with no affect

-I sprayed around the base of the carb and intake with no change in idle

-I maxed out the fast idle cam and there was zero increase in RPM.

So, what internal circuits in the carb would cause it to act this way?

d1

 

Can you verify that when you move the FI cam follower it is moving the throttle plate? The FI mechanism is a complicated bit of kit and I get confused every time I look at it. The key thing is not to get frustrated, and play with it until you see how it is supposed to work.

 

And so we don't miss something, nothing else was done other than a carb change? No distributor install, no plug wires changed, etc.?

 

I took off the carb from the intake to verify the FI linkage operates the throttle plates. In doing so, I also noticed holes drilled in the throttle plates and blackened marks on the gasket where the idle bypass holes sit over (see pictures).

Will the holes in the throttle plates cause me the issues I am having? I can replace them with a solid set if need be.

d1

 

Correct, I took off the holley which had a 1 inch spacer to help clear the 3711 EGR plate and slapped on the Q-jet with no spacer.

d1

 

We still don't know how much vacuum you run at idle, and that's essential to know in order to know how the carb should be set up.

It is possible that your carb is sucking too much air in through the holes in the throttle plates, which is messing up the air/fuel ratio obtained from the idle jets.
It's also possible that it's all just right.

- Eric

 

I guess I could pull vacuum at "idle" if I force the throttle open more. I don't have any apparent vacuum leaks either. But as it stands the current idle rpm, if it doesn't die first, fluctuates between 500 and 700 rpm with all vacuum ports capped. To me, the idle circuit does not seem right at all... adjustments do not seem to increase rpm at all, timing advance doesn't affect it all... it's perplexing to say the least.

For reference, the Holley I had on there resulted in 13 Hg of vacuum at curb idle (850 rpm).

d1

 

Well, you have the idle air bypass, AND the drilled primary plates to accommodate more cam. It appears the carb was done by a knowledgeable technician.

I am stumped now, but I will say that if you changed the timing and the idle speed did not change.... that ai not right.

Apply a vacuum gage.