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Quadrajet problems...

11K views 126 replies 15 participants last post by  d.b. cooper 
#1 ·
i'm thinking of just getting a holley 4175, not because i don't like quadrajets, but because i don't have time to dork around with a q-jet.

Anyways, what recently happened, after running ok is now i have no idle and i'm getting flooding.

The only thing i did was to adjust the secondary throttle plates to open more (the plates, NOT the air flap doors) and then did some "spirited testing" let's just say.... The jeg's reman q-jet shipped with the secondary plates really not opening at all. i got them to open about 30-40 degrees which is enough for now. i did this Monday night.

So, Tuesday morning, immediately after doing an acceleration test, i immediately noticed that the low speed and idle wasn't normal/as smooth as before. After work, i did another "test." After highway cruising about 15-20 mins came to a stoplight. Engine was really idling rough at this point. Then, at this stoplight, did another "test." After this is when the stalling/no idle/flooding happened at the next stoplight. This was Tuesday and before this everything ran fine.

-----timing very advanced but don't think this is the problem.

---- Choke works fine

---- fuel pressure last time i checked was about 5.5 lbs at idle. As soon as i open throttle it goes down to about 2.5-3.5.

---- "Normal" WAS 1000rpm neutral, 600rpm in gear. Won't do any of that anymore. If i put it in neutral and keep my foot on it i can get it to idle 800+rpm all day, as soon as i let up it putters out.

So to Sum: Engine will no longer idle and getting flooding. Ran good until immediately after adjusting the secondary throttle plates to open more and after doing acceleration tests.
 
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#39 ·
I know this is on a Holley which is what I use on my builds. On the needle and seat the size makes no difference on how well it will handle the pressure in my experience. The main thing that makes the difference is the fuel pressure going to the needle and seat. I have ran stock .097 size needle and seats and the more performance size .110 size needle and seats on many different Holley style carbs over the years and it made no difference on how they reacted to fuel pressure.

If I had to much pressure both would flood in no time flat or if they got junk in them. I never had problems before with electric or mechanical fuel pumps back in the older days but three years I had to finally go to a fuel pressure regulator because of the modern fuel boiling to quickly vs in previous years and also a lot of the mechanical fuel pumps on small block chevy's for some reason can end up with pushing out over 9 psi out of the box. Never had that problem in the early 2000's but since the later years past 2010 I have read a lot of folks getting new pumps that are supposed to run no more then about 6 psi but end up at the 6 to 9 psi mark and that will make a carb flood very quickly regardless of what size needle and seat you use.

I got a return style fuel pressure regulator to the fuel keeps moving and to help combat fuel boiling when the vehicle is turned off and I have mine set at 5.5 psi and it has worked like a charm for me. Its almost recommended to run a return style line nowadays because of the difference in fuel compared to how it was years back. Fuel injection has been the standard for so long that the fuel is no longer really good for carbs along with the added ethanol which only complicates things. Get a book on how to rebuild Qjet carbs that Cliff Ruggles made and you can learn a lot about those carbs and it has a lot of good tips in it and on rebuilding etc.
 
#41 ·
Yep, i got the book.

i checked the mechanical advance springs. They are not stuck,binding or broken and move freely. i also checked the vacuum advance and that is not stuck either. But, that wasn't the problem to begin with..........?

i'll keep everyone updated. i am busy at work along with personal stuff, which is why it's taking a while, but i am halfway thru the "rebuild." More of a "refurbishing." I did get an "SR" rebuild kit from Cliff.
 
#43 ·
Nope----still doing it. Baffled.


i am only getting 3lbs fuel pressure according to the new gauge. So i don't think that is the problem.


So, to recap:

1) All i did was bend this tab to get the secondary throttle plates to open; The secondary plates really did not open at all when i first got the carb. i got them to open to at least 70%.



(This is not the actual carb in question though.)

2) Did an "acceleration test."

3) Immediately after the "acceleration test," did the symptoms start: i can't keep it running below 900-800ish rpm if i take my foot off the pedal. After it stalls out, it's very difficult, if not impossible to start, unless you wait 30mins. to an hour. Then, it starts.

Could moving that tab cause other problems? It must be something simple, but i'm baffled.

May go holley 4175 at this point.
 
#44 ·
Is there a chance that maybe you might have worn throttle shaft and its taking in air and you have a vacuum leak? That could maybe be your idle problem but I can't say for sure. Qjets are known to have the front shaft go bad and round out the throttle shaft bore and you can fix it with a bushing. I have only worked on one Qjet in my lifetime and that was over 15 years ago so I wish I could think of something on what it could be. If you got a Holley 4175 I would put it on and rule things out and see how your engine runs.

Sounds like you might be having some sort of fuel problem or ignition problem if you can't get your car to start and having to have it sit for a half hour or more before it runs again. One thing that can be there is if your carburetor is getting so hot that its boiling your fuel and it can cause hard starts.

Is there a chance that maybe you have a problem with your distributor control module if you are running an HEI type? Don't know what your running for that. I know a control module can get hot and make a hard start condition as well. I am just trying to think of some things you could check. I don't see how you just adjusting a tab on your carb could cause a bunch of problems but weird things have happened before with some of my stuff carb wise.
 
#45 ·
Is there a chance that maybe you might have worn throttle shaft and its taking in air and you have a vacuum leak? That could maybe be your idle problem but I can't say for sure. Qjets are known to have the front shaft go bad and round out the throttle shaft bore and you can fix it with a bushing. I have only worked on one Qjet in my lifetime and that was over 15 years ago so I wish I could think of something on what it could be. If you got a Holley 4175 I would put it on and rule things out and see how your engine runs.

Sounds like you might be having some sort of fuel problem or ignition problem if you can't get your car to start and having to have it sit for a half hour or more before it runs again. One thing that can be there is if your carburetor is getting so hot that its boiling your fuel and it can cause hard starts.

Is there a chance that maybe you have a problem with your distributor control module if you are running an HEI type? Don't know what your running for that. I know a control module can get hot and make a hard start condition as well. I am just trying to think of some things you could check. I don't see how you just adjusting a tab on your carb could cause a bunch of problems but weird things have happened before with some of my stuff carb wise.
1) Could be, but i doubt it based on visual inspection. i agree you can't 100% tell by visual inspection. Plus the carb doesn't have many miles on it.

2) i don't think ignition is the problem. Yes, i'm running an HEI, but if the module was getting hot why would it run above 1000rpm just fine indefinitely?
 
#46 ·
i can't get it to start now. It did start this morning; i pinched off the pcv line just to see if that was the problem. It wasn't. Now i can't get it to start. i think something in the idle circuit is blocked.....?

Funny how trying to make it faster (and it DID go faster briefly) has now made it so it doesn't go at all......

i'm basically done for now. i think it's best to stick with one thing at a time---namely the suspension and chassis (see my other posts).

i thought it would be more exciting to do it this way, but i don't think this is the most intelligent way. This way i can devote 100% effort towards solving the problem. i kind of want to solve it because i feel we are close----it HAS to be something simple. And, i'll learn more about carbs this way. Rather than to just buy a new carb or EFI, although i have not ruled those out either.

i'll check back in a few weeks.
 
#47 ·
I would say it might be something simple and trust me I know it happens. I just recently had a Holley carb that I put together last year and calibrated and had nothing but issues trying to get it to run and it was as clean as new, and it just would not run and hardly idle. I then put a backup carburetor that I have and it was only calibrated on the idle air bleeds a hair richer and when I put that other carburetor back on a few months back I was stumped as to why it would not run.

The backup carb that was on my truck, I took it off and sold it to make some quick cash to pay for my wife's alternator for her vehicle. I tried this and that and checked everything and just could not figure it out and then looking back at my notes which I always make when I tune a carb on any change I make to it and noticed the difference in size on the rear idle air bleeds and believe it or not, that was what ended up being my problem. I never in all my years experienced that much of a difference in a carb tune for just a tiny size difference in a idle air bleed difference, but sure enough changing it back to a different carb I put together with the previous backup specs I stuck it on and it ran like a charm.

All I need to do is fix the rear idle air bleeds and put it back a few steps richer and it will be good to go. First time and it was just as simple as an air bleed change. That takes some customizing since they are not changeable, but I can make mine that way with my taps and a set of brass allen screws. Good luck on your build I am sure you will figure it out and perhaps you just got something inside your passages somewhere that somehow got past your fuel filter and got mixed in there somewhere and a quick carb spray and perhaps a spray of air will get it out.

Has happened to me before.
 
#48 ·
i've decided that the mature, intelligent thing to do would be to solve the problem; What good are 14x32 slicks and a trick strut front suspension (see my other posts) if you can't even get the engine to idle? Those things will come.

No, i will stick with it and at least try to find out why.
 
#49 ·
I’ve had two carburetors in my lifetime that crapped out in a similar way one a 800 CFM Q-Jet the other a 900 CFM Holley 3 barrel. Same symptom of crappy idle and primary circuit throttle control, but both would scream once nursed into the secondaries. Never found the cause on either after putting years of work into chasing passages, gasket alignments, minute inspections, rebuilds and tests repeatedly never changed a thing. When doing a major move I just dumped them in the trash after years of taking them out for a fresh look. They whipped my technical butt and that doesn’t often happen.

Bogie
 
#50 ·
Reminds me once of a brand new Holley 670 street avenger I got that was junk out of the box and never thought it would be a carburetor issue. My engine would run fine during warmup and then after that it started to fall on its head and could not idle for a dang and you had to keep giving it fuel to keep my truck running and I checked the ignition system and went over everything and never once suspected the carburetor since it was brand new out of the box but after days of messing around with things my Father finally said it has to be the carburetor as we had been through everything else.

Sure enough he had an old 600 Holley that was rebuilt sitting on his work bench and he installed it on and boom, everything was just fine once again. I got a new Holley after that and replaced the street avenger with another one and it ran fine after some tuning but things can just go bad for some reason and no amount of checking and doing this or that can fix it in the normal world with an abnormal situation from a carb. That is why now I have spare parts and other things to replace stuff if something goes bad and can replace it if after going through everything else does not fix things.
 
#52 ·
Still doing it.......

i went back and cleaned out all the idle tubes, passages etc. more thourougly with compressed air and ran a wire thru all of them. i'm "pretty sure " all the passages are clear because when i blow thru one end, i can feel air at the other end. For Example: Blowing thru the main jets i can feel air coming thru the idle tubes and vice-versa etc.

The only other thing i did was to back off timing just a little. Then i tried running it again tonight. It seemed to run a little smoother and even below 1000rpm it seemed a little better (smoother--- if puttering out can be described as "smooth".) But it's still stalling below 900 unless i give it some pedal intervention. Also, as before, i can't restart it unless i wait at least an hour.


i think now we should list ALL the possible reasons why an engine would stall out below 1000rpm. All the reasons AND in order of likeliness.

i would even like to suggest we make a sticky conerning this topic.
 
#53 ·
UPDATE:

i did find that the line to the vacuum advance is leaking. BUT, this is connected to ported opening; So, would this cause stalling?

My hunch is no----- The stalling happens at curb idle and the throttle plates are closed (or nearly closed) and thus the port opening really isn't getting any (or much) vacuum anyways? Thus, this would not be enough to cause stalling?

P.S.
i am trying to follow the above suggestion of investigating each and every possible reason for stalling in order of likeliness and will report back with more detail
 
#54 ·
Also, i don't know if i mentioned this before, but before the problem happened, i could easily start the engine cold with one press of the pedal to the floor---release---and the engine would start within one revolution of the crank and a lot of times LESS than one revolution of the crank. i mean it would start faster than any of my fuel injected cars.

Now, i have to really crank for maybe 10 seconds and it sort of wants to start and it will start but not earnestly.

Warm, i can now get it to start, but also with lots of cranking. Whereas before i might have to crank a little and then press the accelerator 1/3 the way to the floor and it would usually start pretty easily.

So what would hard starting tend to indicate?
 
#55 ·
Electrical as in distributor or coil or plugs is what this sounds like.

Try firing it with a small prime of fuel no pumping of the carb. Then try it with a shot of starting fluid. If it reacts the same as when you try to light it up off the carb you probably have the direction you should be looking.

Bogie
 
#58 ·
More things to check:
Vacuum leak at gasket under carb...
Vacuum leak inside power brakes booster...
Vacuum leak inside HVAC controls/servos...
Vacuum leak in automatic transmission servo...
Leaking PCV...
Checked all that and have blocked off PCV and brake booster, just to totally eliminate those as possible leaks even though i don't think they are leaking.

when it shuts off and you work the throttle, does fuel spray out of the accel pump discharge?
Yes.

UPDATE:
i am still dilligently working on this, but don't want to reveal too much until the problem is solved for fear of making a bigger mess of the post and further leading us down the rabbit hole. The title "quadrajet problems" was irresponsible to begin with.....
 
#59 ·
P.S.
OFFICIAL STATEMENT:

IF the problem is not solved by July 9th, that's two weeks, then i will likely quit and go back to pursing women; i actually find it easier to get a woman to go to bed than to fix a car. And i'm no casanova either. i'm no Smokey Yunick or Dale Armstrong either, but that should be obvious....
 
#62 ·
Figuring out a carburetor problem is a lot easier then trying to understand women and there problems. Been married 21 years and still can't figure things out with my other half at times lol. Keep working at it and don't give up. Its times like this that it will give you a heck of a lot more experience and in future times when problems arise you will be able to figure them out a lot easier and tune even better.

Trust me when I was 18 years old I did not know even how to adjust the idle on a carburetor let alone troubleshoot one. I only knew how to check and fill fluids and that was it. It took me a lot of years and reading and experience and to a lot of folks helping me on here that has led me to where I am now.
 
#64 · (Edited)
Anyways, back to the problem:

It has worsened:
Replaced pickup coil with an AC Delco unit because i tested the one in there and the OHMS went all over the place as i moved it back and forth----to simulate vacuum advance. They still stayed within spec----500-1500 OHMS but they did move wildly as i rotated the pickup and i heard that the OHMS reading should stay put when you move it. This likely had nothing to do with original problem as after i replaced this pickup coil, the engine did start but would not stay running below 1000rpms---which was the original problem.

Replaced Coil and module with AC delco units. Then replaced all 6 plugs with new delco R43T's:



i can get a better picture if necessary. Plugs 4, and 6 has gas on them, plug 5 was oily, but all three have dried up by now.

The engine now will not start.

Now keep in mind that after i replaced the pickup coil, the engine did start and run. There is no need to remove or reposition the distributor to change out the module or coil so the distributor IS NOT out of position or out of time, and the plug wires are all in the correct order.
And i'm getting spark, at least thru the wires as indicated by the in-line spark tester. As the engine did run before changing the coil and module, it's likely that spark IS getting to the plugs.

Starting fluid didn't work.

i think at this point, we should list causes from most likely / or root cause, to the next likely and so on and so on.

OR, if we want to continue with the "it could be this," or "it could be that," approach this is fine too. Don't get me wrong, i appreciate any and all help. In that case,let's list ALL and ANY possible reasons why the engine won't start.

Remember, If the problem is not solved by July 9th, then i'm quitting cars and going back to women.
(Note: i will suspend time for transit----for example fedex screwed me over as i was supposed to recieve the coil and module on friday, but did not recieve them until yesterday. And fedex is a subject for another thread....)
 
#65 ·
P.S.
It has been 2 months and 64 posts and the problem is not only not solved, but it has gotten worse.

Part of me DOES NOT want the problem solved; i'm sort of like Charlie Brown---i get a neurotic pleasure out of NOT solving the problem. i want to see how long the thread can be stretched to try to get a non-computerized carb and distributor engine running, just to see how messed up things can get----sort of like a trainwreck.

This is sort of like neurotic entertainment for me in an unhealthy way.
 
#66 · (Edited)
It really sounds like either fuel pump or ignition.

Most common to worn throttle shafts is you cannot get the idle speed down unless you cut off the fuel flow as it is getting sufficient air around the shafts. Given new Q-Jets haven’t been made since dinosaurs roomed the earth your unit is most likely a rebuild so unless it was a shop that bushes the throttle shaft bore it is as old as the carburetor was newly made.

I’ve had carburetors that just died, never could find the cause, repetitive cleaning, micro inspection and kit rebuilding never exposed or improved the problem. Replacing the carburetor solved the problem immediately so it wasn’t fuel delivery, ignition or cam ot it’s timing set problem. Of those that did this they were Holley’s and Q-Jets, I can’t remember a Carter now Edelbrock, or Ford 2100 or 4100 series doing this. That said a long time ago a woman I was dating had an early 1980’s Ford station wagon that every now and and then would just stop running when sitting out a traffic light. It had fuel and spark but would not run till it sat for a few minutes then it would fire up and run fine till next time. She traded it for a Honda. So some of these problems are essentially unsolvable, in the case of the Ford in question, hours of inspection in the shop where of course it was running never exposed the problem. You would need the shops resources with you at a traffic light when it quit. By the time you had it towed to the shop, it would start up by simply turning the key on start and away it would go. So it’s hard to fault find when the fault isn’t displaying.

Now back at your problem with a time element for recovery, this speaks strongly to fuel supply and or ignition. This would include tank venting and weird things like some object being drawn into the fuel pick up which could range from a cigarette filter in the tank to a flex line that the interior has a peeling surface that reduces to cuts off fuel flow to where once the forces are removed eventually corrects itself. A pressure test with observation when this happens may reveal this. Idling with a functional hot spot under the plenum might cook the fuel out of the bowl flooding the engine and requiring a cool down and cylinder venting to get a restart.

This also fits a heat sensitive ignition module and or the timing sensor if your distributor separates these functions.

Oily spark plugs do not dry out but fuel wet plugs do.

A common SBC vacuum leak which includes making oily spark plugs is the intake gasket leaking on the valley side so it is not visible. This is really common where the block has been decked, or the heads milled, or aftermarket parts of head’s and intake are used where fitments, machined angles, and tolerances stack to allow gaps in sealing the intake to the head’s. Another common one
especially where screw in rocker studs are used is vacuum leaks into the ports around the threads of the studs. Valve guide to stem clearance is another problem especially with bronze guides.

Bogie
 
#67 ·
It really sounds like either fuel pump or ignition.

Most common to worn throttle shafts is you cannot get the idle speed down unless you cut off the fuel flow as it is getting sufficient air around the shafts. Given new Q-Jets haven’t been made since dinosaurs roomed the earth your unit is most likely a rebuild so unless it was a shop that bushes the throttle shaft bore it is as old as the carburetor was newly made.

I’ve had carburetors that just died, never could find the cause, repetitive cleaning, micro inspection and kit rebuilding never exposed or improved the problem. Replacing the carburetor solved the problem immediately so it wasn’t fuel delivery, ignition or cam ot it’s timing set problem. Of those that did this they were Holley’s and Q-Jets, I can’t remember a Carter now Edelbrock, or Ford 2100 or 4100 series doing this. That said a long time ago a woman I was dating had an early 1980’s Ford station wagon that every now and and then would just stop running when sitting out a traffic light. It had fuel and spark but would not run till it sat for a few minutes then it would fire up and run fine till next time. She traded it for a Honda. So some of these problems are essentially unsolvable, in the case of the Ford in question, hours of inspection in the shop where of course it was running never exposed the problem. You would need the shops resources with you at a traffic light when it quit. By the time you had it towed to the shop, it would start up by simply turning the key on start and away it would go. So it’s hard to fault find when the fault isn’t displaying.

Now back at your problem with a time element for recovery, this speaks strongly to fuel supply and or ignition. This would include tank venting and weird things like some object being drawn into the fuel pick up which could range from a cigarette filter in the tank to a flex line that the interior has a peeling surface that reduces to cuts off fuel flow to where once the forces are removed eventually corrects itself. A pressure test with observation when this happens may reveal this. Idling with a functional hot spot under the plenum might cook the fuel out of the bowl flooding the engine and requiring a cool down and cylinder venting to get a restart.

This also fits a heat sensitive ignition module and or the timing sensor if your distributor separates these functions.

Oily spark plugs do not dry out but fuel wet plugs do.

A common SBC vacuum leak which includes making oily spark plugs is the intake gasket leaking on the valley side so it is not visible. This is really common where the block has been decked, or the heads milled, or aftermarket parts of head’s and intake are used where fitments, machined angles, and tolerances stack to allow gaps in sealing the intake to the head’s. Another common one
especially where screw in rocker studs are used is vacuum leaks into the ports around the threads of the studs. Valve guide to stem clearance is another problem especially with bronze guides.

Bogie
Thanks. However, wouldn't the ability to idle at 1000 or above [if i keep my foot on the gas or if the carb is on hi-step /choke still engaged, (assuming i can manage to get it started at all at this point...)] indefinitely indicate that is is likely NOT fuel or spark that's the problem?

Also, since i've replaced everything in the distributor, likely this rules out that the module/coil/pickup coil on the HEI only works at 1000rpm and above?

The only thing i can think of at this point is the idle tubes or something in the idle system of the carb is screwed. But how could BOTH passages get plugged in just one night?
 
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