Quadrajet Gurus, I need your assistance

I've got a quadrajet problem that has me scratching my head on.

For the past 4 years I've been running a Quad on my Galaxie and had a lot of sucess with it. Car started acting like it was missing at idle, more throttle the more bogging, hesitating, floor it and it nearly dies. Acts like its over-choked, even though when warmed up I wire the choke open.

Ok, so rebuilt the carb and did a really bang up job. New brass float, set at 13/32", all the passages blown out, cleaned the hell out of it but it was pretty clean inside, barely any sediment in the float chamber. Put on and the car idles sweet, ran great, better than it ever has....for the first 1/2 mile, then back to its old self.

I can put my hands over the airhorn and it will die in about 3 seconds which makes me think there isn't a big vacuum leak causing problems, as its also not lean popping. Inlet fuel filter is clean. All vacuum ports are plugged. Ignition is brandy new Duraspark firing a Mallory Hyfire IVa box with radio supression core wires. Car ran the EXACT same after the new igntion install a few weeks back.

I'm going to pull the plugs tonight and regap to .050 for the new CDI ignition and pull the fuel filter in the fuel pump, but I'm doubting that will be it. Any ideas of items to try?

 

Did you seal the plugs on the bottom of the float bowl before you put the base plate back on? BIggest problem with the Q-jets is that these plugs always leak after a while causing the motor to run rich. Best indication of them leaking is that it will take a while to start after sitting a while cause all the gas runs out of the bowl into the intake.

 

I doubt if it's the well plugs. Only the early models had this problem.
The newer ones had the plugs installed with a different process.
Besides ,it wouldn't act up at an idle . Those plugs would cause the bowl to leak down overnight, or several days
Most likely, the needle and seat aren't sealing and the bowl is too full.
What are you using for a fuel pump?
If the bowl is too full ,when you shut it off warm, it'll create a bunch of steam ,or vapor from the primary side.
What is the original application of the carb?

 

Lack of fuel pressure or lack of timing advance as said above..Secondary air flap could be stuck open. Check the exhaust damper not stuck shut on the exhaust manifold.

 

You have to re do the fuel wells , The leaking is couseing a rich and flooding the motor. Its commond with the late Q jets also shave 10 tho from the fuel pump shot,

 

That is true about it not cleaning itself out. I did miss that,but he is describing a rich condition, atleast some of the time. LOW fuel in the bowl wouldn't make it idle rough.

 

What would the effects of ethanol cause any of the symptoms described?

 

Take a BFH and beat the bejabbers out of it. Go buy a holley or a carter, edelbrock or a stock ford autolite. Put a adapter on it and run a 2 bbl. OldWolf

 

I had the same symptoms a few years ago, on a 51 that had a fabric/rubber braided covered fuel line from the hard-line to the fuel pump inlet. Drive it a while, then it would starve. Found the line had deteriorated inside, swelled up and was restricting fuel flow, not enough for normal idle and slow going, but as the need for more volume, the fuel level in float bowl was getting lower. I figured the unleaded with ethanol was the cause of the internal swelling. I had bought it from a man that hadn't ran it for about 20 years, ran great for me for about two weeks, then the problem developed.

 

Tell us more about the engine. Does it have hard seats in the exhaust? You may want to do a compression test. Sounds alot like my '40 before I went through the heads. Ran like shit.
Jeff

 

Simple fix, buy a Holley.

 

Great idea, but BFH 's don't work on Qjets . Only on all that primitive stuff you mentioned. How about Strombergs? A real hot rodder would never forget THEM.

 

You need to look a little newer, like late 1970's. They had electric chokes. I worked at a salvage yard back in the 1990's and salvaged alot of metering rods and jets. Built up a nice collection. I used to run a dual 4brl intake with quadrajets. It worked great with the small primary and a progresive linkage. Still have it.
Jeff

 

Running a points ignition?

Points that have the rubbing block so worn that the points are almost closed will mimic carburetor problems.


A lean stumble can be caused by a bad PCV valve.


Been there, done both - in Fords if ya can believe it....

 

Wow, lots of good feedback and some not so good. No, I wont go full retard on the thing with a BFH. Seriously, once you see how good this carb can be, you'll never want to go back. I've still got the old autolite 4100 on the shelf, which is where it will stay forever.

I did notice that the air horn gasket is a touch discolored, not wet looking, but you can tell fuel is saturating it on the front of the carb. Would this indicate something or do they always look like that after a rebuild?

I didn't get out there last night, got home late. Some answers to some questions:

- Engine is all stock 1962 z code 300hp factory motor except for freebie aluminum edelbrock performer rpm intake. Was suggested to recheck the torque on the intake bolts, will do that.

- Carb is a '76 model, ID# 17056202, 800cfm with electric choke conversion.

- Well plugs are sealed already, though I do know they leak a little bit. If the car sits for longer than a week or three it will drain the bowl. I run the thin type 4 hole gasket and was told the bowl will percolate after running hot and sitting and will lose some gas with that gasket. I'm not sure if its leaking well plugs or the thin gasket that is actually the issue there. Would have to be one hell of a leak wouldnt it at operating rpm? Car idles decent, air mix screws do have an effect, it just acts like it misses occasionally, maybe 1-2 times a minute at idle. Misses, bogs, hesitates and just acts horrible off idle. Not lean popping, so its a rich fuel condition from what some of you have said.

- It has a brand new needle and seat, and the seat assembly is the non-window (leakdown type). Needle is hug on the center of the hanger, NOT clipped through the hanger hole by mistake and its a new brass float.

- Ignition is brand new, I can tell it is running better, but had no effect on the problem. Timing set at 14 btdc and vacuum advances nicely to ~30 degrees. This motor has always been a bit finicky about the timing, below 12 and it starts acting pissed and below 10 it damn near wont idle. Stock cam is advanced 3 degrees.

- Will check the secondary air flap, it springs back as it should and really, it shouldn't even be opening since I'm never in the secondaries yet. Actually, would probably be better to wire it shut until I figure out what is jacking up the primary circuit

- Will check fuel pump and pressure. Pump is only a year old. Need to check the rubber line betwen the pump and hardline to the tank, good idea there.

- Heads are redone and only have 10k miles on them. Not popping back through the carb though, so I dont think its seats. You can hear it popping in the exhaust, but its not a loud backfire, but you can hear it under your feet when it acts up off idle.

- PCV valve working correctly.

- Placing the car under load at idle in Drive or Reverse, the idle gets super choppy, misses, bogs. Park and Neutral it idles ok, but with the occasional miss mentioned earlier.

 

All that'll fix is the wallet of whoever sells you the Holley.

 

It sounds like it could be in the power valve or accel. pump. I'm sure you looked and made sure you are getting a pump on both primarys. Did you check to see if the piston for the metering rods on the primarys is free. Could be sticking in the bore, or a weak or broken spring.

I would do a compression check, I was told years ago it's the first thing to do when you do a tuneup pn an engine running bad. Then I would pull the valve covers and make sure you are getting full lift on all of the valves. Could have a flat cam as well. I have also hooked my inductive timing light to each plug wire and watched for a break in the spark. If you gap the plugs get a new set and swap them in case you have a bad set of plugs. Good luck!!!
Jeff

 

Man, your description is classic for a fuel system that's barely able to support the motor. Check the pump & lines.

The throttle equals bogging is your answer. Since the carb was clean you know it's not a debris issue that's resurfaced. So it musta been a supply issue.

good luck

 

I had a Q jet that did the same thing. It would start and idle but it would sputter out when you revved it a few times. I figured it was a fuel supply issue and checked the pump which was working. Pulled the filter and it looked clean. Then I checked the needle and seat and it wasn't clogged but while I had the top off the carb I turned the pump on for a second and hardly any fuel was coming out. Just for the heck of it I pulled the filter out, tried the pump again and it looked like old faithful. The filter looked clean but must of had a layer of "varnish" clogging it up.

 

i had a q-jet problem once and my dad told me of this quick fix. first pull the carb, then put it on the work bench and disasemble and then rake all those parts in the trash and put a decent carb on it. i know i felt the same way we he got to the last step

 

have you checked the power valve, i forget which hole but one of then on top of the carb you can put a small round rod in and make it go up and down with the engine off, then with the engine ideling you can do the same, engine off no vaccum and the valve should be up and you can push it down, engine running it should be down and wount move at all. i love q-jets

 

Why on earth would you wear ignorance like a badge of honor?

Let me guess...... you installed a holley with the choke wired open, set the idle speed, used whatever jets, accelerator pump cam, and power valve was in the carb.... then learned how to baby it thru the dead spot while talking shit about qjets. If that's accurate we'd probably make great friends in the real world cause you sound like most of my buds.

 

Oh, come on, Shifty, quadrajets MUST be awful....there are lots of Holley decals in quarter windows, but I've never seen a quadrajet decal! I've put used q-jets that have sat on the shelf for years on cars and had them run fine; try that with a used Holley, and you'd best be standing by with a fire extinguisher.

 

So, what? You guys couldn't figure out how to put it back together?

 

Right with y'all. You pretty much took the words right outta my head!

Let 'em use their Holleys - I get more good Q-Jets that way... full ice cream bucketloads of 'em!

~Jason

 

Q-jets are darn good carbs. They have issues, but so does every other carb.
The fact that it worked for a bit then got bad again is telling. You don't mention driveability above idle. Have you driven it, or is it so bad it won't go? If so, I'd also suggest a new fuel inlet filter which is something that should be part of the rebuild. IF that doesn't cure it and all the motor checks are good, I'd say you need to pull it back apart. Also, are the shaft bores worn? I've seen a lot that can change the RPM at idle by a couple hundred, and they can't idle right with that kind of vacuum leak. Blow out the Idle circuits and check the transfer slots carefully. If there is room, run the thick base gasket. Did you do the acc pump check ball reseat? Take the old ball and with a punch, carefully smack it once to ensure the seat is smooth. Replace the old ball you just dinged with the new one from the kit.

 

had a warped lid give similar symptoms as well as transfer tubes at the improper depth. they can shake loose over time and if the fuel level isn't quite right it'll cause you hell.

 

I love q-jets. The flack I got in highschool for refusing to go to the dark side of Holley was never ending. As others, it gave me a nice source of carbs to salvage parts from.

Anyway,
1) Fuel filter. Just replace it. Make sure the side with the hole in it is facing the fuel line. You won't see if its dirty unless you rip it open.

2)Dirty tank? rubber line going? ripping open the fuel filter will help narrow it down. If you do find junk in the filter, you'll need to open up the carb and blow out the passages again (crap *will* get past the in-carb filter, I now always put an additional inline filter after the fuel pump. GK69M in metal, GK69PL is a small see through plastic one 3/8" inlet and outlet. ACDelco GPsomething-er-other that has slipped my mind in a larger metal can). You can do this on-car.

3)applies to newer cars, usually GM, if you find small black particles in the fuel bowl clogging stuff up, thats charcol from the charcoal cannister and getting sucked into the carb via the purge line. Plug it, or replace the cannister.

Alex.
Give me your unwanted Q-jets! =-)

 

LOL!

No shit, dude!

~Jason

 

This is especially noteworthy for those trying to run junkyard or otherwise unknown source used carbs. That 3/8" angled vacuum port on the front goes right into the float bowl and connects to the charcoal can.

You'd be wise to flip the carb so it's upside down and nose down, then flush it with some cleaner over a pan. If any small pieces of charcoal come out, you need to take the top off.

If somebody removed a Qjet from a car made in the 80s because it was running badly, this is the #1 reason. The float is being restricted by charcoal bits.