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Discussion Starter · #1 ·
Once upon a time I knew how to adjust the choke and fast idle cam on a 1969 Rochester Quadrajet, with divorced choke but 30 years have left me foggy....

I recently installed a rebuilt 7029203 DY I purchased off a member here. It starts great in warm weather but the past two days the garage has been under 40 degrees at start-up. I press down all the way and release and crank. The choke is engaged BUT the choke blade flapper is shut tight - no air - no start. :sad:

If I manually manipulate the choke assembly cam to the second choke setting on the cam the blade flapper opens enough for the car to start but she is a little rough until the choke heats up a bit and opens wider. :thumbsup:

How do I set the flapper adjustment on the fast idle cam to open more on the highest cam setting? I thought there was a screw adjustment on the cam for the blade flapper rod, but I only see what I think is the screw for the fast idle speed.

Pictures speak a thousand words :)

Thanks in advance

Brian
 

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2 things:

1. Make sure you have the right gaskets if you used a cross over intake, or heat riser (not sure what the right name is). If the idle circuits are exposed it will make it do all kinds of crazy things.
2. Choke should be closed tight when cold. As soon as the engine fires the choke pull off will engage and open the choke blade about a 1/4". Then as the choke warms it will fall through (I think) 3 steps until its off the entire way.

If it's running rough from too much fuel, fat, then the choke blade is closed too much. I replaced the choke pull off and the vacuum blader hole was not open, had to drill it out. Drove me nuts trying to figure out why it wasn't pulling the choke off.

I can post pics later this week, out on the road for work....
 

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Discussion Starter · #3 ·
It is on a hot slot intake but I use the correct "tin" and "fiber" sandwich gaskets so no binding there to worry about. Mixture is okay, I got max vacuum on the gauge when tuning.

The vacuum choke pull off only blocks the secondaries from opening on this carb, the divorced choke rod controls the primaries and I can't remember for the life of me how you adjust the opening. Seem to remember using a feeler gauge or a drill bit to hold the opening at the right gap then you adjust something and then pull out the feeler. Its not complicated at all but can't find my Rochester service manuals.
 

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If I remember correctly (and it's been many years), the linkage between the vacuum choke pull off and the choke butterfly has bends down and then back up and can be opened up or closed up slightly to fine tune how far opened the choke butterfly is once the engine starts. To adjust, open throttle so choke butterfly closes (when cold), connect a hand vacuum pump to vacuum choke pull off and pump it up both verifying the diaphragm is leak free and to cause the pull off to pull the linkage to the open/running position, and use a 1/4" drill bit to check the gap between the partially open choke butterfly and inside of carburetor air horn. Adjust the linkage by bending slightly if necessary.

I think there is also a mechanical "choke unloader" linkage so that when the throttle is held to the floor or wide open, the choke butterfly is mechanically forced partially open. Can't remember how far open but it helps get an engine that is over choked or even flooded to start easier by over riding the choke if/when necessary by holding the accelerator pedal all the way to the floor.


It is on a hot slot intake but I use the correct "tin" and "fiber" sandwich gaskets so no binding there to worry about. Mixture is okay, I got max vacuum on the gauge when tuning.

The vacuum choke pull off only blocks the secondaries from opening on this carb, the divorced choke rod controls the primaries and I can't remember for the life of me how you adjust the opening. Seem to remember using a feeler gauge or a drill bit to hold the opening at the right gap then you adjust something and then pull out the feeler. Its not complicated at all but can't find my Rochester service manuals.
 

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Discussion Starter · #5 ·
Thanks Scott that sounds right with using the drill bit as the feeler gauge, that I can remember doing as a kid, but I'm still at a loss as to the pull off and how it works, as it is only connected to the secondaries butterfly blade from the diaphram. When the vehicle is running the choke pull off holds the secondaries closed tight and I can't budge it. And when I shutdown the rod releases and I can push and pull so I think the diaphragm is okay IMHO.

The mechanical choke un-loader if it is the weighted lever on the side, is what I have been using to step it to the second high idle on the cam so the flapper gets some air into the carb so it can start. I can do "WOT" and have the choke cancel so that is working just fine.

But if you depress the pedal all the way to the floor then release the choke engages on the top of the fast idle cam settings the blades are shut tight and no matter how long you crank you get nothing, but open them just a small gap by forcing the choke to use the second highest setting, or wedging a matchstick into the blades and she starts right up. I'm afraid to use the matchstick much for fear it will be sucked into the intake. :) I'm not that smart at times. Bust as it gets colder I will need the top setting.

Brian
 

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Now this pea brain is confused. A vacuum diaphragm (dash-pot) on a Q jet secondary? The dash-pot should be in plain sight and connected to the choke. The engine should start and cause its vacuum to pull open the choke. Maybe I read your post wrong Brian. Pictures?
 

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I have been fighting a new Jet stage 2 for weeks now. If not the choke, it idles too fast, idle, it's a bog, if not a bog, it's flooding. :confused:

Just when I THINK I have it, the sucker takes forever to crank. I put my worn out quadrajet back on to keep my sanity!
 

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Brian, I dated myself (old) and proved the 'pea brain' part.
Dash-pot is the flinky that slows the throttle closing so the engine doesn't stall. The choke pull off diaphragm is just that. Two separate components. I'll shut up now.
 

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Brian,

Can you take a photo (a few would be even better) so we can see exactly what you are talking about related to the choke pull off being connected to the secondaries rather than the primary choke butterfly?
 

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Couple of things:
- choke blade needs to be fully closed when cold
- at start up the vacuum pull off needs to open approx. 1/4" * this is the drill bit thing
- choke being on at all blocks secondaries, has nothing to do with vacuum pull off.

Here is a link to post the will tell you everything you could ever imagine about these carbs.

http://www.digitalcorvettes.com/forums/showthread.php?t=88376


Procedure from the thread:

1. Divorced Choke Systems (1967-1974)
 Disconnect the divorced choke rod from the lever on the passenger side of the carb. Leave it attached to the choke coil box on the manifold.
 Open the throttle slightly and fully close the choke by pushing on the lever arm that the disconnected rod normally attaches to.
 Push the choke rod all the way down into the choke coil until it hits the stop. If the engine is dead cold, it may already be bottomed out.
 At this position, the top of the choke rod should be level with the bottom edge of the choke rod hole in the lever on the carb.
 Bend the rod to obtain this relationship.
 Once complete, hook the rod back up to the lever.
 With the rod hooked up, push the choke rod back down to the seated position once again. This should fully close the choke blade. If the choke blade is not fully closed in this position, bend the choke intermediate rod that comes up through the body of the carb and attaches to the choke blade lever. Bend the rod so that the choke blade is fully closed.
 Remove the short piece of vacuum hose attaching the choke pulloff to the vacuum nipple on the carb. Attach a long (about 2’) vacuum hose to the pulloff.
 Crack the throttle slightly and push down on the divorced choke rod to close the choke fully. Release the throttle. Keep light finger pressure on the choke rod to maintain light closing pressure on the choke.
 Suck on the vacuum hose to retract the choke pulloff. If the pulloff does not retract, it must be replaced.
 With the pulloff fully retracted and light finger pressure on the choke rod, use your other hand to lightly push down on the forward lower edge of the choke blade to simulate to force of the air across the blade. This will open the choke slightly. At this point, measure the distance between the forward lower edge of the choke blade and the forward wall of the airhorn. This distance should be ¼”. You can use a ¼” drill bit as a simple gauge to check it. To adjust, bend the tang on the choke linkage where it contacts the choke pulloff rod.
 Re-attach the vacuum hose to the pulloff and the carb.
 

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I've rebuilt/tuned-up two Quadrajets since 1970 and used the model year shop manual. To this day I've not seen a FI engine that ran better.
 

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Discussion Starter · #12 ·
okay Scott I have attached a few photos to clarify this mud. No problem Fred been there done that.

If I trace the linkage from the secondaries top flapper to the vacuum diaphragm aka choke pull off, that is all it seems to be connected to. All four q-jets I own look all the same. So maybe I'm not seeing any connection to the primary top choke flapper, but I'm doing so on all of them. Am I missing it? So this choke pull off diaphragm vacuum pot or whatever you want to call it - how should it be connected to the primaries and open the flapper when under vacuum. That is the part that confuses me. The divorced choke rod seems to only interact with the primary and the fast idle cam. The fast idle cam does seem to function as the lock-out of the lower plate of the secondaries.

Garth - Thank you very much for the details since the link site you sent was down for maintenance early this morning and just came back up but I don't have the time right now to read all the way through it but sounds like a good start since I could not find the Rochester Q-jet Service Manual for 69 on-line. What I could find was all about modifications to jets and metering changes, or is for non original Rochester Q-Jet clones that have no manual/divorced choke adjustments, only just electric choke units.

I was thinking that I either have to bend the rod to the primaries to leave the 1/4 drill bit diameter opening under highest choke as Scott described - which sounds very familiar - deja vu or is there some interaction with the two screws on the fast idle cam that I would need to adjust the opening with. But seems that the answer is to bend the rod. The fog on that in my head is clearing. Now if I can only figure out how the vacuum choke pull off needs to be connected to the primary choke rod.

Still mud or can anyone else see the bottom yet?

Note: These pictures were taken with choke not set, engine not running.
 

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Brian,

So the number of years since I've worked on these indicates my original explanation was incorrect. I found the following adjustment diagram, poor quality but readable. Does this help (I'll keep looking for additional information as well)?

 

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Discussion Starter · #15 ·
Brian,

So the number of years since I've worked on these indicates my original explanation was incorrect. I found the following adjustment diagram, poor quality but readable. Does this help (I'll keep looking for additional information as well)?

You know I like visuals - my phone is having issues opening the thumbnail where I am so I'll open and print it off when I get back home!
 

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Discussion Starter · #16 ·
Was just about to post the same instructions that Garth did further up. If you follow those, you should get it straightened out.
Yes it all seems like something I did before - like a lot of things - so simple it's complicated. :)
 

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Discussion Starter · #17 ·

Mud gone and seen the bottom...
So I came home and put my non progressive lens glasses on LOL and took a close look at the choke pull off. I looked at my other Q-Jets and tested and WTF. The reason I didn't notice last night that the two interacted was due to the lever highlighted by the RED arrow was bent so far forward that it never engaged with the pull off rod at the point where the GREEN arrow highlights, when the rod movement indicated by the BLACK arrow bottomed out at the pull off. It still had an eighth of an inch before it would have started hitting the pull off rod.

So I looked at the other three Q-Jets I own, they all are bent but the curve is higher on one and catches the pull off rod sooner, the other two including one that is factory sealed in its original shrink wrap and box never opened are also slightly bent.

I may have mentioned that I had purchased this recently rebuilt Q-Jet from a TC member. The unit had been restored by Cliff a few years back. So I was scratching my head and wondering how he could have ever got his 69 SS/RS L48 started in the winter with the lever never being touched by the pull-off rod's bend. So I did a search and sure as shine-ola he had posted a cold weather starting thread back in Dec 12 - I even responded to it LOL. He stated on Jan 13 that he had resolved his starting issue - that he had rebuilt the carb with a new kit from Cliff that past summer but the screws were now loose and once he tightened her back up the problem went away. :yes:

In any event I bent the lever indicated in RED back while the pull-off was receiving vacuum from my pump till it met the bend in the rod indicated by GREEN, then I inserted a 1/4 inch drill bit as per the adjustment directions and the lever is almost straight up now. Did I bend the right part? The diagram that Scott posted said to bend the tang. Garth's post said rod so I'm at a loss there.

Of course I wanted to test but I found that I had seriously flooded her out mucking around with the throttle so much. :D I waited a bit then did a flooded start which did idle on the fast idle cam until I stepped it down so the choke is working. I test started her a few hours later after dinner but she was still semi warm. It started right up and was in mid cold fast idle. I'll test Thursday when stone cold and see if I'm on target. Unless someone tells me I seriously bent the wrong part and I need to reverse it, and bend something else.

All things said and done I think the fast idle is a bit low at 1020. I'll pull the Chevrolet Service Manual and see if it lists a rpm for the highest point of a fast idle. Mark in his cold start thread mentioned he had the fast idle set to 1200 but I assume my changing the curb idle down to 700 also lowered the fast idle since I think I remember on the Q-Jet they share roles and are not independent.

So thanks to all of you for your help. I'll do some searching tonight for more adjustment pictures. I'll post the results of the stone cold start too. :popcorn:
 

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Well that's progress at least, glad you are on your way if not there already.

I've got a Quadrajet from a Mercury I/O boat engine that I need to go through for a friend of mine so this was good timing for me to re-familiarize myself with the Quadrajet technology.
 

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An easy way to test the unloader is: pull the vacuum hose off, compress the lever, put your finger over the hose nipple blocking air flow, release the lever. It will stick out a tiny bit, then stop if it's good. If it's bad, it will fully extend.

The most common Q jet problems are:
1, Heavy float causing it to idle rich from high float level, failure to pass smog test. The float can absorb modern fuel, didn't with the old stuff.
2. Bad choke pull off (unloader) causing rich idle, hard starting, black smoke.
3, Bad accelerator pump seal. Usually attacked by fuel. Failure to take throttle.
 
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