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Old 09-30-2013, 12:02 PM
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quadrajet problems......jets.

im having trouble passing smog. timing, idle speed, and mixture are near perfect. after getting it diagnosed, tech said the jets are possibly too big and im running too rich, 13.5-13.9. how do I know what size jets I have and witch ones to get.

oh yeah, by the way, the idiot before me ground off the numbers on the carb so im kinda screwed.

it is a 4bbl QJ on a 307 sbc.

thanks,
Cpl. Boyd U.S.M.C.

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Old 09-30-2013, 02:01 PM
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Quote:
Originally Posted by severed head View Post
im having trouble passing smog. timing, idle speed, and mixture are near perfect. after getting it diagnosed, tech said the jets are possibly too big and im running too rich, 13.5-13.9. how do I know what size jets I have and witch ones to get.
oh yeah, by the way, the idiot before me ground off the numbers on the carb so im kinda screwed.
it is a 4bbl QJ on a 307 sbc.
thanks,
Cpl. Boyd U.S.M.C.
Thanks for your service Corporal.

What would I do? I'd box it up and send it to Cliff Ruggles to be rebuilt.
Cliffs High Performance Quadrajets :: Qjet Carburetor Rebuild Kits, Parts, Quadrajet Rebuilding, Quadrajet Parts, Bushing Kits, Carb Tuning
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Old 09-30-2013, 02:04 PM
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thank you.
do you know off hand how much??
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Old 09-30-2013, 02:22 PM
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thank you.
do you know off hand how much??
I don't know, it depends on the work he will have to do to bring it back to operational condition. Call him up......740-397-2921
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Old 09-30-2013, 03:50 PM
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Cliff's presently on a backlog. Get in line!! Could be 6 months till he sees yours.
Your jets might be perfect. You're likely idling on the power circuit and have totally uncovered the transition slot.
What's your vac advance hooked to? Ported or manifold?
What's your initial timing?
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Old 09-30-2013, 04:23 PM
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Last time I spoke to him there was a ~6 month wait and the cost for a complete rebuild (not refinishing the zinc chromate or replating the hardware- just the internals) was around $200. Worth it if you're not able to do it yourself.

The thing you need to determine if you want to try rejetting it yourself, is whether your Q-jet has the large air bleeds like used on some Chevy carbs, or if the bleeds are smaller. If you don't know what jets and metering rods are in it now, you need to pull the top off the carb to see. Once you have the rod/jet sizes, you can inspect the carb to see what the bleeds are and we can go from there.

If the carb has an adjustable part throttle setup, you need to be sure it's tuned correctly, else that can hurt emissions. So can the wrong power piston spring- it works the same as a Holley power valve and if the spring is too strong, it'll be too rich under any load and possibly even at idle, although the a/f ratio you cite would seem to eliminate that as a possibility.

To try to narrow it down some, which carb does it most resemble from the two below? The pdf is by a guy, "Lars" who has compiled quite a bit of info on stock jetting, etc.
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Name:	1974 Cad, 7044530 tunnel, small air bleeds, old casting, side inlet, divorced, front av po, hook.jpg
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ID:	85482   Click image for larger version

Name:	BUICK V6 17080244 1980 4.1L 252cid throttle arm side view.jpg
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File Type: pdf Q-Jet_Carb_TuningLars.pdf (651.1 KB, 41 views)
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Old 09-30-2013, 04:30 PM
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Why dont you post your test results as they will supply us with the info we need to help straighten out your car.
I assume you failed the 25/25 test? Which gas caused the fail? NOX CO HC CO2 ???
knowing which one can narrow down the area of concern.
Dont do anything until you know which direction to go.
Excess hydrocarbons can be caused by worn rings or a number of things.
Excess NOX can be caused by too high compression and no EGR action (if equipt)
Check the numbers first, that will give an indication of which direction to go.

I would be glad to help anyway I can....Thanks for your service to our great country.
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Old 09-30-2013, 04:40 PM
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Post a couple picture of the carb as well. It should be pretty easy to ID.
Jets wont have anything to do with Idle. Idle channel restrictions and Idle air bleeds will be the trouble if it fails at idle.
At cruise (25/25) it is on the main circuit (jets) and metering rods, APT as Cobalt mentioned and power piston spring could be coming into play.

Dont rule out other mechanical problems. Weak rings, carbon build up in the cylinders....
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Old 09-30-2013, 05:24 PM
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This may help a little
Carburetors: Recarbco - rebuilt carbs and carburetor troubleshooting
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Old 10-01-2013, 10:09 AM
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Try to rebuild it yourself. If you have some mechanical skill or interest in the hobby, you will benefit from understanding how to use the carburetor. Buy cliffs' book. I rebuilt my Qjet with his advice. In book examples, it used the same performer cam I installed. His best formula was spot on. The vacuum pods need to be timed right, and the ATP system understood. The book will explain the systems of the Qjet.

You can tune it pretty well with a old O2 sensor and DVOM. Dial it in as well as anybody.

I would try.
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Old 10-01-2013, 10:59 AM
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First of all, I would look up the carb number. Q-jets were mounted on many engine types. Each type of Q-jet, has a particular set of jets and rods to start out with, according to the engine they are sitting on. And lets not forget to check that throttle shaft for play. A vacuum leak there will through things off as well.
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Old 10-01-2013, 03:28 PM
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Quote:
Originally Posted by Denny View Post
First of all, I would look up the carb number. Q-jets were mounted on many engine types. Each type of Q-jet, has a particular set of jets and rods to start out with, according to the engine they are sitting on. And lets not forget to check that throttle shaft for play. A vacuum leak there will through things off as well.
He stated that the numbers have been ground off...also a quadrajet never came on a 307 as a stock piece.
That is why I asked him to post a pic, at least we can narrow it down and probably figure it out after the jet numbers are exposed.
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Old 11-14-2013, 04:08 PM
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https://www.facebook.com/photo.php?f...size=960%2C720

here is the picture of the carb. I hope it helps.
the only gas that was high is CO. I believe it indicates a rich condition. it passed the idle gasses but failed the 15\25 with high co. i'd have to grab the paperwork and see what the exact measurement was, but I believe passing CO was 2.?? and I failed at 3.?? any ideas? if you need more info or pictures. let me know
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Old 11-14-2013, 04:37 PM
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Hi CO is a rich condition. Seeing that it passed at Idle and not at part throttle acceleration, I would have to say the guy at the testing station was probably correct.It needs jetted down.You could put a lighter spring under the power piston , this may help keep the metering rods in the jets farther, leaning it out some at part throttle acceleration (15/25)
Idont suspect the float level or a soggy saturated float as it passed at idle.Problem is in acceleration enrichment (metering rods-jets power piston)
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Old 11-14-2013, 04:49 PM
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Here's a place that sells the springs.
Power Piston Spring Assortment - Rochester Quadrajet Carburetor Parts
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