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Seems the carb is supplying too much fuel, as indicated by the black plugs, and won't restart immediately after shutting off even though it has fuel and spark but is likely flooded. you would have to keep the revs up for the engine to move enough air to not flood.
 

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Discussion Starter · #82 ·
PROGRESS!

Ok, i just got it to go down to about 700rpm with no pedal intervention. It was rough but i think i need to tweak the idle mix screws. (When i recently rebuilt the carb, i set the idle mix screws 8 turns out)

i did a little more reading and i think the problem is/was that the primary blades were not open enough at curb idle. Mine appeared to be fully closed all this time.... Now, i don't know how the hell they got like that but i theorize that when i adjusted the secondaries (plates, not air flaps) to open more i somehow "twisted" the primary throttle arm in relation to the shaft or blades? Or possibly the cable wasn't completely stretched and allowing the throttle stop to touch the idle screw or something? Because i'm pretty positive i never touched the curb idle screw when i adjusted the secondaries.

On pg. 26 of Cliff's book, it states, "The idle system is activated when the primary throttle plates are nearly closed." Now, this, to me, doesn't make it clear whether the throttle plates SHOULD be nearly closed at idle, it just says WHEN the plates are nearly closed....

Doug Roe's book makes it pretty clear in many places that the primaries are slightly open during curb idle. Pg. 46, 100, and more.

In all the GM service manuals, one of the first things listed under troubleshooting in regards to the fuel system and stalling is idle speed screw out of adjustment. i ignored this because i figured there was NO WAY this thing went out of adjustment. How could it? It didn't vibrate loose? But i guess it somehow went out of adjustment, or i put it out of adjustment----likely when i adjusted the secondaries because that is exactly when the problem started.

Seems the carb is supplying too much fuel, as indicated by the black plugs, and won't restart immediately after shutting off even though it has fuel and spark but is likely flooded. you would have to keep the revs up for the engine to move enough air to not flood.
So, my theory here is that when you start when the engine is cold the throttle IS already at least slightly open on hi-step, mid-high step, and low-high step on a q-jet as the choke goes thru it's range so i was able to start it (although, it became more difficult to start immediately after i messed with the secondaries).

The way i usually start when engine warm is to not touch the pedal at all unless it won't start, in that case continue to crank and slowly press the pedal about 1/2 down. But since the throttle was completely closed----(warm choke equals no hi-steps and now we're on the curb idle screw), i couldn't start it because the engine wasn't getting enough air? And i was then flooding it, which made things worse?

When i first saw the plugs all blackened, this concerned me and will have to be addressed. The carb i'm using is actually jetted for 305's and 350's (Jeg's reman #15805). This may be a little rich, but, at the time, i figured 305 was the closest thing to 262. It does otherwise run ok.

The other thing is that the AC R43t's are considered a "colder" plug, so there's that too.

Sorry ladies, looks like you'll have to wait longer......
 

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Idle stop screw should be about 1 to 1.5 turn in after making contact with lever making primary blades open, this will just crack the blades and allow them to work with transfer slots and pull gas from mixture screws. 1 to 1.5 is an common average.

I have never seen idle mix screws 8 turns out, normally about 3 is an average.

My guess is that your carbs idle circuit has been alter to allow more fuel at idle for larger cams. Thus my thinking is 8turns out is dumping a lot of gas.


One way to see if you to far open on idle stop screws, is if you can turn idle mixture screws all the way in and closed or you turn them and it has no effect on rpms, then your primary blade are open to much. This causes you to be running on primary circuit.
 

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Don't feel bad D.B., I have been working on Holley carbs for many years and know my way around them quite well and I can say that its always a little thing that you would never find out right away that can make you want to pull your hair out. I had a similar experience like you one time to where I had set my idle on my truck for about 900 rpm idle in park and it would drop to 700 rpm in gear. I then had my electric choke off at the time which I unhook during the summer months as I don't obviously need it.

After I had set it and verified that the choke was opening up all the way and stuff and then set the fast idle setting on it, it was after that point that while I was driving my truck that my idle would not go below about 1000 rpm while in park and at times would seem to get stuck and not stay consistent in the setting even though I verified everything.

I chased for a vacuum leak and found nothing, I checked the idle setting and it was fine and I knew my primary throttle plate opening was correct as I verified it before setting it on and I checked my timing and all kinds of things and could not for the life of me understand why that thing was just doing that after I set my choke up and it was all adjusted like it normally is done. I kept playing with this and that and checking it like a fine tooth comb and just did not figure out what the problem was. At that point I got desperate and took my carb off to look at the electric choke mechanism and when holding my carb up and then releasing the fast idle cam I could see where it was doing its job like its supposed to but after holding it up to the light and you can't set his this from the side but only by either using a mirror if it was on the engine or if you held it up over your head and look underneath it.

On the Holley if you have the fast idle setting up to high of an rpm the fast idle screw makes contact on several steps on the fast idle cam and is not supposed to make contact with it once the choke is all the way open. I found the fast idle screw was just vary faintly making contact with the fast idle cam even in the fully open position and I had to lessen my fast idle rpm setting just a few hundred rpm to where the screw no longer made contact on it when it was fully open. After that minor adjustment all my problems went away and after spending about a week checking a bunch of things everyday for a while before getting tired of it.

Ever since that time when ever I set up my carb that is one thing I check for before installing so as to not have that problem again. Sometimes just a simple over site and something out of the ordinary can make a big problem out of a tiny fix that is needed. Glad that you are finding it out and knew you would.
 

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Yeah, the idle fuel screws usually are 1.5 to maybe as much as 3 turns out. The primary throttle curb idle screw is set maybe 2 turns open with the fast idle cam of the choke released, setting the fast idle on the choke is both how much preload is on the choke bi-metal coil and the fast idle screw. The choke coil sets how much or how many steps up the fast idle screw sits on the fast idle cam while the fast idle screw allows control of the idle speed while the choke is in a closed position. As the choke opens the fast idle cam falls out from under the fast idle screw, this usually takes a light blipping of the throttle to allow release. Eventually the fast idle screw and its cam separate and idle speed is then set on the curb idle screw that stops the throttle lever.

The references in your book are about how the idle fuel circuit works which being under the throttle blades when they are nearly closed which the curb idle and even the fast idle cam maintain the idle fuel ports are subjected to manifold vacuum which is pulling fuel from these ports. Even fast idle doesn’t require much opening of the throttle to achieve. Without a working load on the crankshaft it takes very little opening of the throttle blades to achieve a substantial RPM.

The next circuit that activates as the throttle is opened is the transition circuit. This usually is a rectangular port above the round idle fuel port. Proper throttle blade curb idle adjustment is with about .020 to not more than .040 inch of this port exposed measured from the adjacent bottom surface of the throttle blade when the throttle is resting on the curb idle screw. This is set on the bench before installation on the engine. Given you can’t see this adjustment once the carb is installed it is a good idea to paint the lower throttle bell crank and the adjacent carb body with Dykem and scratch lines indicating these position limits. Getting the curb idle too far open that excessive transition slot is exposed will result in a rich mixture that is uncontrollable from the idle fuel screws and a flat spot in engine performance transitioning to main metering. The transition slot feeds off the idle circuit ahead of the idle fuel mixture screw. Big cams cause problems with this circuit because they need to idle fast resulting in enough throttle opening to fully expose the transition slot. To prevent this hot rod engine builders using a carb with only idle circuits on the primary throttles have to drill small air bleed holes in the throttle blades so they can be properly adjusted in regard to the transition slot. The other option is the purchase of a 4 barrel carburetor that features idle circuits on all four barrels. There are some carburetors that use an external idle air bleed in which case the curb idle is set with its screw control and not by cracking the throttle, the Q-Jet is not one of these. Some original Carter AFB’s used this but the follow on Edelbrock Performer (AFB) does not. Some Holley models use this with an adjustment screw located under the air-cleaner stud.

The Q-Jet, also, can develop an excess fueling problem with leakage past the main metering well plugs on the underside of the carb. These are not visible without removal of the carb from the intake. This was a chronic problem back in the mid to late 1960’s but GM eventually got it mostly solved.

Your idle fuel adjustment was so far from normal I know I never considered it. A fast idle resulting in a stall when trying to slow it down is also common to a failing timing set where the cam is falling retarded to the crankshaft and very common to failing ignition components especially the Hall or magnetic sensor depending on which is used and very common to a failing module. It is also a common symptom of a vacuum leak which has many possible sources among them being the vacuum advance canister’s diaphragm or that of the EGR valve and for hot rod built engines with top end parts from different sources and lots of machining is a common source is an internal leak from the valley into the intake ports due to fitment issues between the head’s and intake as dimensions and manufacturing tolerances are vary from those of GM.

I guess the give away that I at least missed was the plugs come out wet and oily but dry off in a few minutes. This, obviously is fuel because oil doesn’t dry except in very long periods of time if then.

Anyway I glad you found the problem and have it fixed, welcome to root cause analysis it can sometimes be a bear to figure these things out.

Bogie
 

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Discussion Starter · #86 · (Edited)
As far as the idle mix screws:
i have a later 80's casting that came with the fine pitch thread screws. Cliff, of Cliff's quadrajets, said 8 would be a good bench setting for these, but i'll check again. Before the rebuild (which was likely also a waste of money and time, the only consolation is i'm now more comfortable removing and taking apart q-jets) i had the mix screws about 7-7.5 turns out. So when i rebuilt it i figured i'd go richer to try to solve this problem.

So, i'm hearing that fine pitch screws need to be turned out more turns, the coarse pitch threads not as much----maybe 4 turns, although i'm hearing from you guys and other sources, 1.5 to 2 turns out as a bench setting? i'll do more research.

After sleeping on it, i THINK this may have happened:



(NOTE: This is not the same carb as on the engine, but the linkages are exactly the same.)

In order to adjust the secondary blades (not air flaps), you have to bend tab "A" rearwards, towards the back of the carb/car so that it contacts tab "B" Tab "B" is connected to the rod that connects to the secondary throttle shaft etc. If you want more opening bend it further, less opening bend it less.

However, you'll soon notice that when you try to bend "A" rearwards, the throttle arm "D", ALSO moves rewards /clockwise because they are connected to each other. So, you have to find a way to stop the throttle arm from moving to have any chance to be able to bend tab "A."

So what i did was grasp the throttle arm and hold it still as i attempted to bend tab "A" with needlenose pliers towards the rear of the carb.

In doing this, i MAY have judiciously turned the throttle arm counter-clockwise---in order to counteract the forces of trying to bend tab "A" rearwards. In doing THAT, tab "C", the throttle arm stop that contacts the curb idle screw MAY have bent rearward, toward the rear of the carb-----thus allowing the primary throttle plates to close more than they usually do? ( Because by bending tab "C", this allowed the throttle to turn more counter-clockwise and thus closing the throttle plates more) i didn't think that tab "C" could bend by hand, but i just tried it on this above carburetor and yes, they can bend without a tremendous amount of force.


i'm not saying this is absolutely 100% what happened, but i can't see any other plausible explanation as to what caused the problem. Coupled with the fact that this problem occurred only IMMEDIATELY after i performed this modification on the secondaries.

i hate to put it this way, but this is sort of like an NTSB investigation after a plane crash or something.
 

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Discussion Starter · #88 ·
the rod from the primary to the secondary should rattle around freely when the throttle is at idle
It does.

Also, the overall issue isn't really solved yet; While the part about not being able to keep the engine running without pedal intervention "might" (although i now have my doubts) be solved, which i considered to be the original problem. But now i either can't get the engine started, or if i do it's with a lot of cranking and even then it kind of only putters to a start instead of normally catching. Before all this, the engine would start within one crank revolution or less.

This no start/hard start condition also happened exactly after i messed with the secondaries. So, i'm thinking the overall problem really isn't solved-----what good is an engine that can now idle, but can't be started?

And i'm beginning to think my above "theory" about bending the throttle arm may be bunk.

i think my destiny is to quit cars/racing and to start socializing with women again and to just be miserable. Why fight it......
 

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Discussion Starter · #90 ·
Find a woman that knows about carbs.
1) Far fetched----i'll have a better chance figuring it out by myself. i would have a better chance changing a fan belt----with the engine running.

2) Speaking of understanding women----and at the risk of getting myself banned in light of in this day and age:

WOW......
 

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Discussion Starter · #91 ·
Anyways, back to the problem:

It has worsened----i can't get it started and i have no credibility. i will not report positive unless and until the truck actually starts and moves on the road----not idling in the driveway and does not stall out or have any other abnormal behavior.

i wasted my whole vacation trying to figure this out and made virtually no progress. i could have went to Arizona and had fun with friends----speaking of women and carbs, i know one in AZ who used to work at machine shop AND HAS A Q-JET (but doesn't understand it----she got pissed at me when i tried to adjust the choke. That is one thing i CAN do...) Some 80's chrysler trucks were equipped with q-jets.

This has become a virtual trainwreck----this is a non-computeried carb and distributor. This is not fuel injection (although, at this point i'm thinking that's the better way to go....for me...)
 

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Discussion Starter · #92 ·
UPDATE:
Ok, we got a little off track there. i will try not to do that anymore.

i feel we now have four separate problems:

1) Engine won't staying running below 1000rpms.

2) Engine won't restart after stalling unless you wait an hour, but recently won't start at all.
(#1 and #2 were the original problems)

3) Engine won't start cold.

4) Engine turns over slowly when cold even with battery fully charged. This may be due to the battery needed to be replaced as it's 11 yrs old although still reads over 12V and/or the starter needs to be replaced possibly due to poor quality and/or due to all the cranking lately.
 

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Discussion Starter · #93 ·
UPDATE:

Starter likely hosed. Battery tested good with load tester. Voltage drop on cables is good. Can't take care of it until the weekend.

Haven't given up........yet.
 

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Discussion Starter · #94 ·
UPDATE 7/4;

Legitimate progress:
Put in new starter and got the engine to stay running at 800 rpm with no pedal intervention. It only stalled after i turned in one idle mix screw too much. Now, this is actually pretty close to where it was before the fiasco started----idle was really never that great and something i really needed to get right, but never got around to it.

But i think we need to suspend this thread so we can take care of the more pressing issue.
 

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I don't know how much more I would take if I was in your shoes. I one time many years back worked on a Qjet for a 88 Chevy Caprice with a bone stock 305 small block and it was my brothers car and his car ran ok when he got it but over time it would run rich and just blow the black smoke out the exhaust pipe and the engine itself was in good condition and the ignition was good but his Qjet had some sort of computerized components on it and I took the carb off and looked it over and took it apart and even bought a book on rebuilding Qjets and watched videos and it just got to be such a hassle I told him were going to get rid of the computer stuff.

Long story short I bought him a old school Hei distributor and then I bought a used Holley 600 vacuum secondary off of ebay for less then a hundred bucks. I had to get one of those spread bore to square bore adapters and rebuilt his carb for him and put it all together and just wow what a night and day difference and he had no more issues anymore. His fuel mileage was not that bad and not to much different overall vs before his Qjet went south.

For the rest of the time he owned his car it ran like a top and nothing against a Qjet they are the best carb you can get for the best fuel mileage and fuel metering vs a Holley or Edelbrock style carburetor but when it comes to fixing those things at times they are a pain in the rear.

After the Holley was on it was such a breeze to adjust it and get it running good and he was always a happy camper with it after that. It ran good till he sold it to get a truck but it was worth the little bit I put into it for him to get rid of the old worn out Qjet. They are good carbs when they work but when it comes to trouble shooting them, they can be a bit of a pain compared to others. It seems like your really close and am missing just a tiny thing somewhere.
 

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Discussion Starter · #96 ·
Yeah, i'm actually a little depressed about this, but we're probably very close so i'll probably stick with it and forget about the whole july 9th deadline.

Now the 4175 is still an option, but i think i would like to figure this out----if only to see what the problem was.
 

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Discussion Starter · #97 ·
UPDATE 7/8:

i know i set the deadline for 7/9 for the problem to be solved or i was going to quit cars and be miserable (re-associate with women...).

But i think more realistically a reasonable plan would be:

1) Rebuild (again) this carb, this time taking the idle tubes completely out and making sure they are not clogged or otherwise obstructed. Using REAL compressed air vs. the spray can stuff, which is really for electronics. We are so close. i don't see what else it could be: Ignition good. Not flooding. No vacuum leaks that i know of.
i was never 100% i got the idle circuit clear during last rebuild.

2) If that doesn't work, then rebuild the original q-jet carb i have on the shelf. This is an original core, never been commercially rebuilt (ruined) . Off of a 83 1/2 pickup 305.
If for some bonkers reason THIS carb doesn't work then:

3) NEW Holley 4175. This may not work. Remember v-6's don't have as much space between the back of the carb and the distributor.

4) OR GM TBI

i'm not really meaning to give up, but i need to get this running asap. i have other stuff going on which i'd rather not go into detail right now about.
 

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5)..........EFI............:)(y)
 

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/i would never consider wires an option………..just saying simple is better. Honestly the side hung bowls, Holley is the best option. The shorter version with rear meter plate vs meter block should give more space w/6 cylinder distributor.

IMHO A old carter WCFB rebuilt would be my first choice. Generally pretty cheap at swap meets and e bay. I’m not too sure about adaptor to Q-jet pattern, so that might nix it as an option.
 
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