1980 QuadraJet issues

[Ron Dame]

Thea has 68,000 miles, and generally runs well. Cold starting, however, is an issue, as it's always flooded, even after a week of not driving. Why do I know it's flooded? because if you don't hold the throttle at least 1/2 open, or god forbid, pump the gas, it'll be a while before she finally fires and belches black smoke. Even so, it takes a few moments for all cylinders to fire and there is still some black smoke. Once she's cleared her throat, she runs perfect. Plugs are clean, too.

First, it's not the choke, as I've left it blocked open and on even chilly mornings, it did the same thing.

While a kit is a reasonable start, what areas should I pay special attention to?

[mfg]

3 hours ago, Ron Dame said:

Thea has 68,000 miles, and generally runs well. Cold starting, however, is an issue, as it's always flooded, even after a week of not driving. Why do I know it's flooded? because if you don't hold the throttle at least 1/2 open, or god forbid, pump the gas, it'll be a while before she finally fires and belches black smoke. Even so, it takes a few moments for all cylinders to fire and there is still some black smoke. Once she's cleared her throat, she runs perfect. Plugs are clean, too.

First, it's not the choke, as I've left it blocked open and on even chilly mornings, it did the same thing.

While a kit is a reasonable start, what areas should I pay special attention to?

If your Q-Jet has a composite float, it could be starting to sink due to fuel saturation… I believe a carb overhaul with a new float thrown in is in order here.

When carb is apart, the well plugs at the bottom of float chamber should be checked, as fuel leakage past those plugs has always been a chronic problem with this type of carburetor.

Edited June 10 by mfg
Spell.

[Ron Dame]

27 minutes ago, mfg said:

If your Q-Jet has a composite float, it could be starting to sink due to fuel saturation… I believe a carb overhaul with a new float thrown in is in order here.

When carb is apart, the well plugs at the bottom of float chamber should be checked, as fuel leakage past those plugs has always been a chronic problem with this type of carburetor.

Thanks, that makes sense. I also saw where the well plugs could be an issue, but the post discouraged JB Weld, or similar because heat deltas would cause the plugs to leak again. But no alternatives were given. Do you have an idea?

[ronmanfredi]

4 hours ago, Ron Dame said:

Thea has 68,000 miles, and generally runs well. Cold starting, however, is an issue, as it's always flooded, even after a week of not driving. Why do I know it's flooded? because if you don't hold the throttle at least 1/2 open, or god forbid, pump the gas, it'll be a while before she finally fires and belches black smoke. Even so, it takes a few moments for all cylinders to fire and there is still some black smoke. Once she's cleared her throat, she runs perfect. Plugs are clean, too.

First, it's not the choke, as I've left it blocked open and on even chilly mornings, it did the same thing.

While a kit is a reasonable start, what areas should I pay special attention to?

Your carb is leaking at the well plugs and the float is iffy if stock.  You can get all the parts that you need for your carb model at:  https://quadrajetpower.com/

This Texas based company only offer service and parts on Qjets.  You can supply them with the carb #, which is on the main body of the carb and they can send you whatever parts you need exactly for your carb.  You can also call them for help.

[mfg]

J B Weld offers a higher intensity (stronger?) version that does a pretty good job.. but still iffy!

Some techs have drilled out the plugs, tapped the holes, and then screwed in small brass plugs… I’ve never done this, so I really can’t offer insight on the level of difficulty.

[Ron Dame]

Thanks ronmanfredi and MFG. I hope to get the carb number and order the kit later this week, then I can deal with this. I really appreciate the insight!

[WayneC]

I have rebuilt quadrojet carburetors in the past (I'm too old now), and I sent one to Recarbco in Pittsburgh CA that came back looking like it just left the factory (and performed like it too).

Recarbco is on Facebook (I am not). Not cheap, but excellent work/result.

[mfg]

18 minutes ago, WayneC said:

I have rebuilt quadrojet carburetors in the past (I'm too old now), and I sent one to Recarbco in Pittsburgh CA that came back looking like it just left the factory (and performed like it too).

Recarbco is on Facebook (I am not). Not cheap, but excellent work/result.

That carburetor looks WAY too good to even put on an engine!!! BEAUTIFUL!!

[Zedman]

Hi All- As an aside whilst this thread is open... I have a 1981 EME Carb that I'd like to replace with an un-ECU controlled Quadrajet someday.  Would somebody mind putting up what Carb Code numbers might be a good idea for substitution.  BTW if I do go down this route , the AIR Injection system and Catalytic converter will also be gone too. Charcoal Canister will be staying , however.   Thanks...

 

[mfg]

15 minutes ago, Zedman said:

Hi All- As an aside whilst this thread is open... I have a 1981 EME Carb that I'd like to replace with an un-ECU controlled Quadrajet someday.  Would somebody mind putting up what Carb Code numbers might be a good idea for substitution.  BTW if I do go down this route , the AIR Injection system and Catalytic converter will also be gone too. Charcoal Canister will be staying , however.   Thanks...

 

That is EXACTLY what I did on my ‘83 Avanti when I had had enough of the ‘computer command control’ system!

I ordered a non computer controlled Q-Jet for a ‘78 Impala 350… and also a non computer controlled distributor for same.(distributor has vacuum dash pot)

I made this conversion on my Avanti over 15 years ago… and have never looked back!

And yes, a true dual exhaust system, ‘68 Avanti ll style, also went on!!

[Ron Dame]

The carb number on my 1980 350 is 17080204. It's not computer controlled, thank goodness. It should be perfect for your '81

Edited June 12 by Ron Dame

[Zedman]

On 6/12/2025 at 10:22 AM, mfg said:

That is EXACTLY what I did on my ‘83 Avanti when I had had enough of the ‘computer command control’ system!

I ordered a non computer controlled Q-Jet for a ‘78 Impala 350… and also a non computer controlled distributor for same.(distributor has vacuum dash pot)

I made this conversion on my Avanti over 15 years ago… and have never looked back!

And yes, a true dual exhaust system, ‘68 Avanti ll style, also went on!!

Thanks MFG- I have recently fitted a dual exhaust  (minus Cat- I'll take a risk.. ) whilst the body is off the Frame. The Carb and Distributor are up for substitution after I get the car reassembled and inspected for roadworthy.  I'm looking for an Australian delivery carb that was jetted for the Holden 308 or Pontiac Parisiennes befor the late 70's.

[Zedman]

On 6/13/2025 at 6:30 AM, Ron Dame said:

The carb number on my 1980 350 is 17080204. It's not computer controlled, thank goodness. It should be perfect for your '81

Thanks Ron- I will compare that carb number to the ones I see here in Oz and pick one up eventually.  My 305 will likely require a re-jet smaller , I excpect.

[Ron Dame]

New info: I received my carb kit from Quadrajetpower.com, and began dismantling the carb. The  good news is that the carb is clean inside, has already had the throttle shafts bushed and the well plugs epoxied, so it appears to be remanufactured, though not recently based on the outside grime. Remember the engine ran well, idled well, accelerated well, no issues other than being flooded at start, and blocking the choke open did not help.

What is troubling, is that even with less than 1/2 a tank of gas, fuel keeps dripping out of the fuel line where it went into the carb. (I've not yet completed the carb, so the line is open, save a piece of towel to keep trash out). Best as I can measure, the carb is above the fuel level, though that can be tricky to figure. I loosened the fuel cap to see if pressure had built  up, but no sound of air whooshing, and the fuel keeps dripping.

I'm starting to wonder if either the vapor canister is flooded or the purge valve is bad, causing that, and indirectly flooding the engine after sitting overnight.

What do you all think?

Edited 20 hours ago by Ron Dame

[ronmanfredi]

14 hours ago, Ron Dame said:

New info: I received my carb kit from Quadrajetpower.com, and began dismantling the carb. The  good news is that the carb is clean inside, has already had the throttle shafts bushed and the well plugs epoxied, so it appears to be remanufactured, though not recently based on the outside grime. Remember the engine ran well, idled well, accelerated well, no issues other than being flooded at start, and blocking the choke open did not help.

What is troubling, is that even with less than 1/2 a tank of gas, fuel keeps dripping out of the fuel line where it went into the carb. (I've not yet completed the carb, so the line is open, save a piece of towel to keep trash out). Best as I can measure, the carb is above the fuel level, though that can be tricky to figure. I loosened the fuel cap to see if pressure had built  up, but no sound of air whooshing, and the fuel keeps dripping.

I'm starting to wonder if either the vapor canister is flooded or the purge valve is bad, causing that, and indirectly flooding the engine after sitting overnight.

What do you all think?

If you are saying that gasoline is leaking onto the engine where the metal fuel line threads into the carb body, then the only reason for that is the fitting isn't seating correctly when tightening.  If so, then double check the flare on the line and carb to be sure they are clean and smooth.  If so, then you will use the new filter/gaskets PLUS apply about 3-4 loops of plumbers' tape around the threads of the "Nut" threads to aid in sealing.  You want the tape to only be on the threaded area of the nut.  Be sure both threaded sections are clean before assembly.  A little rubbing alcohol used on the threads before wrapping and installing will help dry off the threads to help the plumbers tape do its job.

[Ron Dame]

Close Ron, but no cigar.

My post wasn't as clear as I had intended. The carb is off being cleaned and reassembled, but the fuel line had dripped at lest a quart before I saw it. I did jack up the front of the car and that fixed that, so it's not really the problem with starting, it's just that the fuel level was higher than the inlet to the carb.

The other question, (now separate from the dripping fuel line), is could the purge valve be causing my flooded starting conditions?

Edited 5 hours ago by Ron Dame

[mfg]

44 minutes ago, Ron Dame said:

Close Ron, but no cigar.

My post wasn't as clear as I had intended. The carb is off being cleaned and reassembled, but the fuel line had dripped at lest a quart before I saw it. I did jack up the front of the car and that fixed that, so it's not really the problem with starting, it's just that the fuel level was higher than the inlet to the carb.

The other question, (now separate from the dripping fuel line), is could the purge valve be causing my flooded starting conditions?

The ‘high fuel tank situation’ has been a chronic Avanti problem since day one!