At my wits end with this QuadraJet

Rktpwrd

Rktpwrd

Royal Smart Person
Feb 2, 2015
1,690
3,321
113
Calgary, Alberta, Canada
#1
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.
 
Z

Zspoiler

Apprentice
Jun 3, 2018
88
30
18
#2
Have you taken it to a shop to check it out.?
 
Rktpwrd

Rktpwrd

Royal Smart Person
Feb 2, 2015
1,690
3,321
113
Calgary, Alberta, Canada
#3
Have you taken it to a shop to check it out.?
Negative.
There’s virtually no one around here that remembers how to tune and tweak these old carbs anymore, and I can’t afford to ship it off to the experts/professionals. It’s extremely cost prohibitive to do that from Canada.
 
olds307 and 403

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
3,326
736
113
Melville,Saskatchewan
#4
My Qjet ran like garbage when I bumped compression from 8 to 1 up to 9.6 to 1, ran fine beforehand. Idle was shit and stumbled bad no matter where my timing was set or curve changed. The idle circuit on those late 70's carbs are super lean, what are your motor specs?
 
Z

Zspoiler

Apprentice
Jun 3, 2018
88
30
18
#5
Do you have a friend who you can borrow a carb from ? to make sure you don`t have any other issues ..Then you can save up to get another carb if necessary .
 
olds307 and 403

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
3,326
736
113
Melville,Saskatchewan
#6
Ken from Everyday Performance, Techg8 on here, rebuilt mine for a good bit less than a new shiny aftermarket carb. Having a core helps a lot for cost. I know our dollar blows, it adds a lot of cost buying stuff from the US.
 
Rktpwrd

Rktpwrd

Royal Smart Person
Feb 2, 2015
1,690
3,321
113
Calgary, Alberta, Canada
#7
My Qjet ran like garbage when I bumped compression from 8 to 1 up to 9.6 to 1, ran fine beforehand. Idle was shit and stumbled bad no matter where my timing was set or curve changed. The idle circuit on those late 70's carbs are super lean, what are your motor specs?
Christian, it’s just a mild small block Chevy build. Stock bottom end, crank rods and pistons. Not even an overbore. 4 bolt mains, thinnest head gaskets possible. New factory Vortec heads, mild cam and Comp 1.6 ratio roller rockers. Stock distributor with MSD HEI coil, aluminum dual plane intake.
Cam specs are in the photo below:

cd29932d-86b0-491a-99ba-d919c96db166-jpeg.90139


There’s absolutely no stumble when it’s running, it just won’t stay running without first revving the piss out of it.
 
olds307 and 403

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
3,326
736
113
Melville,Saskatchewan
#8
That cam is big for a late 70's carb, it sure sounds like an idle restriction issue, idle tubes need opened up. Was the float replaced and level set?
 
Rktpwrd

Rktpwrd

Royal Smart Person
Feb 2, 2015
1,690
3,321
113
Calgary, Alberta, Canada
#9
Do you have a friend who you can borrow a carb from ? to make sure you don`t have any other issues ..Then you can save up to get another carb if necessary .
I do have another QuadraJet that I pulled off a 1980 442 350 Olds in the wreckers last year, but it hasn’t been rebuilt yet and has the center fuel inlet where mine has the side inlet. It also doesn’t have the proper TV linkage location on the throttle shaft for my 200R4, so I definitely couldn’t drive with it.

Throwing it on there just to see if the carb is the problem or not is my next (and last) resort. Problem is, I don’t think that’ll solve the problem.
 
Rktpwrd

Rktpwrd

Royal Smart Person
Feb 2, 2015
1,690
3,321
113
Calgary, Alberta, Canada
#10
That cam is big for a late 70's carb, it sure sounds like an idle restriction issue, idle tubes need opened up. Was the float replaced and level set?
It was verified that the float was sound and not leaking, and the float level was set and readjusted several times. In addition, the well plugs were sealed up too.
 

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