At my wits end with this QuadraJet

[Tim & sleek]

Does it have plastic or brass floats

 

[Tim & sleek]

Hey guys, what’s up.

I’ll get into more particulars of my issue with this QuadraJet later in this thread, but for right now, a simple question:

Is it possible to have a QuadraJet run on the primary circuit rather than the idle circuit?

My car WILL NOT idle on its own after starting it, even if it’s already up to operating temperature. It just stalls. If I very carefully feather the gas and hold the rpms around 800-1000 where it should idle, the engine sounds normal and you can hear the lope of the cam as you should.
But as soon as I take my foot off the gas it just stalls.

The only way I can get it to stay running on its own is if I rev it to 3500-4000 rpm, then it’ll stay running but it’s pig rich and doesn’t sound like it should. Revving it to anything less than these rpms won’t keep it running.

Once it does stay running this way, I can drive the car around for hours through start and stop traffic, and it pulls good throughout the rpm range but as soon as I shut it off and go to restart it the cycle starts all over again.
It’s almost as if when I rev it into this rpm range, it fools the carb into running on the primary circuit rather than the idle circuit. Is this possible?

I’ve gone through countless hours and trouble shooting only to find nothing out of the ordinary. It’s recently been rebuilt, no vacuum leaks, throttle shafts have been bushed, tinkering with the timing and vacuum advance pulloff locations has no effect on the problem. It seems to be an issue with the idle circuit, but unable to determine what. The idle mixture screws are turned out the recommended 3-3 1/2 turns.

The carb was thoroughly cleaned and air blown through all the passages when it was rebuilt, so dirt or contamination is highly unlikely. And yes, I have already bought the Doug Roe QuadraJet book. I see no mention of the problem I’m experiencing in it.

Please help before another QuadraJet finds its way onto the scrap heap. I’m at my wits end with it.

Just asking do u know their is a 800 cfm and 750 cfm and do u know what one u have

 

[Bonnewagon]

FWIW the plastic floats last a long time. But when they go bad and sink it is hard to tell for sure. If you pinch it to see if there is fuel inside then you just ruined it anyway. I like brass and I have never had one go bad. Plus, you can repair a brass one with a soldering iron. I'm sure the factory prefers buying cheap plastic over labor intensive brass, but I am still using the same brass one I put in over 20 years ago.

 

[pontiacgp]

Mark, plus as you know the brass ones are smaller so you have more fuel in the bowl...

 

[olds307 and 403]

Nice work- it looks great. See? At first everyone is intimidated by a Q-jet. But once you dig in and rebuild one several times it gets easy. Then you wonder what all the fear was for. So once the timing is verified start on the carb. A nice trick is to pull out all the plugs and ground the wires. Then have someone crank the motor while you watch the timing light. Now you can set the timing at like 100 rpm and it will not have any advance interfering. When ready, start out at a fast idle and the let it warm up. Then slowly idle down to where you want it. The final adjustment should be while watching the vacuum gauge looking for the most vacuum you can get at a reasonable idle speed. I am confident you will be successful. EDIT: what is that large object above the float bowl on the pass side? That spot is usually used for a high altitude aneroid, the CCC connector, or on some '80's trucks- an idle enrichment solenoid.

I believe that is the 80's truck thing, using electronic's to control the third metering rod. Donovan is there an extra auxiliary metering rod?

 

[Rktpwrd]

Nice work- it looks great. See? At first everyone is intimidated by a Q-jet. But once you dig in and rebuild one several times it gets easy. Then you wonder what all the fear was for. So once the timing is verified start on the carb. A nice trick is to pull out all the plugs and ground the wires. Then have someone crank the motor while you watch the timing light. Now you can set the timing at like 100 rpm and it will not have any advance interfering. When ready, start out at a fast idle and the let it warm up. Then slowly idle down to where you want it. The final adjustment should be while watching the vacuum gauge looking for the most vacuum you can get at a reasonable idle speed. I am confident you will be successful. EDIT: what is that large object above the float bowl on the pass side? That spot is usually used for a high altitude aneroid, the CCC connector, or on some '80's trucks- an idle enrichment solenoid.

Mark, thanks once again for your input and information. It proved to be super helpful yet again.

I did some research some months ago on what exactly that connector is and what it’s for, and it turns out some of the later model but pre-CCC carbs starting in 1980 (which is what mine is) had this provision on them. It’s the “electronic mixture-control” solenoid, same as what the later CCC carbs came with, but without the throttle position sensor that usually accompanies it.
Basically this carb is a predecessor to the CCC carbs, but the solenoid is not (and never has been/was) used. Underneath it it is nothing, it’s simply the connector on the top.

Here’s a picture from Cliff’s book showing the identical solenoid to mine:

I’m off Friday and light duty tomorrow so I’ll keep an eye on this want to know how you come out

Thanks Steve, I really appreciate the interest and all the help you’ve provided. Check out the post following this one to see how I made out tonight.

Does it have plastic or brass floats

It has the nitrophyl float.

Just asking do u know their is a 800 cfm and 750 cfm and do u know what one u have

Yes thanks, I know of the existence of the 800 and 750 cfm models.
This one is a 750, originally off of the 305 that was in the car.

I believe that is the 80's truck thing, using electronic's to control the third metering rod. Donovan is there an extra auxiliary metering rod?

Negative Christian, there’s no auxiliary rod, no nothing. Unfortunately I didn’t take a picture with the top off or I’d show you guys. There’s nothing whatsoever underneath there, it’s just a void linked to the float bowl.

 

[Rktpwrd]

Well gentlemen with your guidance and suggestions, tonight’s startup and tuning session was an absolute resounding success!!

Following Mark and Garth’s recommendations to the letter for setting a baseline to start tuning (5 turns out on the mixture screws, bump up the idle speed, one pump to the floor) I hit the key and she fired right up and stayed running PROPERLY on the idle circuit for the first time since I built the motor!

45 minutes later and after a sufficient warmup period, I did some seat of the pants tuning with my experienced and calibrated ear, as well as with the rpm’s and by the smell of the exhaust.
I now have the car purring like a kitten on the idle circuit, and running smooth as silk!
I need to pick up a dedicated vacuum gauge to further and properly fine tune it more, but it’s already light years ahead of where it used to be. With the engine shut off and up to temp, it fires right up immediately like fuel injection, doesn’t stall, and no longer spits black soot out the tail pipes.

I couldn’t be happier!

After a brief visit with my dad tonight, I took the car out for a short test drive and had zero issues. No off idle stumbles, no hesitations, no pinging, nothing. And it idles properly at stoplights!
As you guys helped me to diagnose and I came to suspect, the issue was definitely within the idle circuit. As I was performing the modifications suggested in Cliff’s book, I found that almost all of the orfice sizes in the idle circuit in my carb were severely undersized from what they should have been for my needs.

I’m not quite done with this beast just yet, I’m quite sure I can get it tuned even better than I have it now, but for the time being I’m gonna chalk this one up in the win column.
It feels great.


Thanks once again to all that contributed to this thread and problem, without your help I wouldn’t necessarily have been able to figure out what the issue was or how to correct it.
A sincere and heartfelt THANK YOU.

D.

 

[O. D. Showtime]

Glad you got it running like it should Donovan, I knew you would. Should be alot more fun to drive now!

 

[1bad79]

That’s awesome I’m glad you saw it through, I really like those carburetors and the way they respond when calibrated correctly

 

[olds307 and 403]

I knew you would come out on top of this. Interesting, someone may have removed or maybe that metering rod was never part of that carb. That is why I like BOP non CCC carbs, I have a 1985 Canadian Olds 307 carb that is non CCC and 800 cfm. Weird that they are all 800 cfm carbs and the Chevies are not. Hopefully your 2004R was properly built, you don't have a leaky aftermarket pan, didn't have the dipstick seal roll on install and have a daughter take the car out of town without you knowing. If those things happen, a recently built 2004R turns into a 2.5 speed trans. I knew you would come out on top, I chickened out at the last minute and took the easy way out. Good Qjet cores used to be everywhere, they are starting to get hard to find.