I purchased a rebuilt, numbers-correct Rochester Quadrajet 4MV for my 74 Corvette to replace the replacement Holley ecomomaster that came on the car. The car ran very well with the Holley initially (I bought the car in 2010 and drove it 6,000 miles with no problems and smooth running), but the car was not used last year and the car wouldn't start after a period of rough running on several start ups due to water in the tank due to a clogged fuel filler drain. I elected to replace the Holley with the Quadrajet and had the tank drained and plugs changed. First was a fuel leak - accelerator pump cup needed replacement. Then the mechanic spent a whole day trying to get it to run smoothly. I provided the manual for the adjustments. He says it's dumping too much fuel. It runs rough like it's missing. I'm almost at the point of having the Holley reinstalled. A local carb specialist will inspect/repair the Quadrajet for 100.-279. depending what it needs which means removing it from the engine again. Does anyone know what could be wrong with this rebuilt Quadrajet. It is from Carb Junkies which has a good reputation. The carb was stored for two years in the box before the installation.







|UPDATED|2/5/2013 10:08:20 PM (AZT)|/UPDATED|


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Lots of things could be wrong....hard to say for sure what exactly the problem is. Sounds like it either has a float level set too high, or there is a massive vacuum leak. Need to make sure it has the correct base gasket, between the carb and intake manifold. Several different versions of this gasket, and it needs to fit both the carb and the intake.
It's possible the carb just sat too long, and is in need of a cleaning, and possibly some gaskets & rubber parts replaced.



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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Google a guy named Lars he is on many forums , he is a q-jet genius. My suggestion if you want a correct running carb is to contact him and send it to him . He can flow it adjust it fix it and from what i have read maybe make it do jumping jacks lmao.. But seriously get a hold of him , send it and when it is back you have a bolt on 100% perfect. 

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1980 , ZZ430 , 3.92 rear , 700R4 2400 stall NEW EZ EFI 

I have had a lot of friends question my choice of a quadrajet carb over other makes.  I am by no means an expert in carbs but from my experience once a q-jet was set up it would run flawlessly for yrs for me.  I'd make sure it was set up right and stick with the q'jet.

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Dave C..........My mantra: I can not be bought!!      Long and short term leases available.

I'll take a Quadrapuke over a Holley ANY day...except on race day....
Quads need to be adjusted properly, and have the correct parts used in them, since there are hundreds of different combinations, and by now, most of them have had parts replaced somewhere down the line.
I went thru the Quad on my '74 before I even owned the car(in 1997)....and other than getting a chunk of rubber fuel line stuck in the needle/seat once, I haven't touched it since.


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

I sent my q-jet off my '81, yep a computer control carb to All American Carburetors in Florida last year and they do not rebuild, they remanufacture the carb. Cost me $300 plus shipping there and back. Installed it and ran perfect, only had to adjust curb idle a little. Been perfect for me since and better gas mileage, well as good as a carb with turbo 350 tranny can do. allamericancarburetor.com is there web site if interested, for me they will do all my future work.

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Tommy

My W.A.G. on this would be float level.  Figuring out what it should be set at is only half the battle, then you have to know how to set it/where to make that measurement.  It is not particularly obvious IMHO.  I've rebuilt two Q-jets now, the original to my '76 and the Edelbrock Q-jet that is on there now.  The first one had lots of weird symptoms and I'm pretty sure now it was a wrong float level that was causing them.  The E-brock unit (not a typical E-brock that's like a Carter AFB, this looks just like a q-jet and uses the same parts) that I'm running now runs great no problems whatsoever.  I eventually plan to rebuild the original the right way and switch back to that, but it will be spendy because I want to get it re-plated first.  

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I second that about Lars.  I will be sending mine off to him as soon as I have time to take it off and get it shipped out.  I have had other so called Qjet experts work on my carb but after talking to Lars there is no question Ill have him do all my Qjet work.  he will also help you set your timing to be all in at the best RPM.  Look him up I'm sure you will be happy as is all the others that have used his service. If you cant find his contact info send me a pm ill get it to you.

Paul

Zen Master Ken (aka kstyer) is a whiz regarding the Q-Jets.  He isn't around as much as he'd like to be but send him an e-mail.  I'm sure he'll have an answer for you.

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Jim Olson 

"The Toys"...!!!  Save the Wave!

Where I've been in a Corvette...!!!

I just had my factory 72 Qjet rebuilt by Lars just the fall.  He even repair the inlet for the filter as it was stripped.  When I recieved it from him, it was literally a bolt on!!  Best the car has run since I had it.  I bought in 1984.  You will not be disappointed!

from what I'm reading, , just as several others have posted, 1. float level 2. needle and seat assembly 3. primary metering rods the float level can be checked fairly easily thru the bowl vent with a float measuring gauge (good luck finding one ) a simple t shaped plastic rule that measures the distance from the top of the float to the top edge of the bowl vent , if there is any trash , debris or more likely dried fuel or solvent between the needle and seat no matter how much time and effort you put into adjusting the float the fuel flo into the bowl won't shut off the primary metering rods move in and out of the primary or" 2 barrel jets" they are finicky and frankly a sumbich to clean, they to can allow over influx of fuel

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I don't think you can adjust or even check float level on a q-jet without taking the top (air horn) off.  9 screws plus choke flapper linkage plus pivot for accelerator pump.  You can do it with the carb still installed, though.  It's one of the annoying things about the design, but it still has enough positives to make it a good choice for me.  

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