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Photos of Some Problems with Commercially Rebuilt Q-Jet
You have all heard my warnings about the issues and problems with the Commercially Rebuilt Q-Jets. I just received another one of these carbs for rebuild, so I thought I'd show you just a few of the issues with these carbs (and why you should avoid them).
I received this Q-Jet number 7040511 (1970 350 Chevy Truck California) from a guy who is running it on a 350 Chevy in a Porsche 914:
Tell-tale signs that it's a commercially rebuilt carb:
Phillips-head screws in the airhorn
Cross-bar block installed in bowl vent hole just forward of the air cleaned stud hole
Black painted secondary rod hanger and black painted choke pulloff bracket
Torx screw installed in secondary rod hanger
Brass fuel inlet fitting
All this doesn't seem so bad - it can be fixed. But they give the carb away as a carb that is likely to have significant other problems. Let's take a closer look and see what they did to this thing...
Look at the way they hooked up the vacuum hose to the choke pulloff. The pulloff is hooked up to ported vacuum. That means that the pulloff would never crack the choke open once the engine starts and idles, resulting in a massive flood-out condition on cold-start:
Check out the accelerator pump rod. The rod is off of a 1975+ carb, and is too long for this 1970 carb. The accelerator pump is almost fully depressed with the carb at idle, which means that there is almost no accel pump shot available when you push the gas pedal down. The carb would have had a horrible tip-in lean stumble:
This is what the accel pump geometry should look like (yeah, I know it's a dirty carb.. I just pulled it out of my parts shed). Notice how much taller the accel pump is sticking up out of the airhorn:
Look at the choke system installed on the carb. The correct 1970 choke system should look like this:
Here is what is installed on the carb. It's a 1969 system. Notice also what they did to the choke pulloff arm: It's bent outwards at a 90-degree angle, preventing any operation and function of the pulloff system. Compare the photo below to a correct 1969 system in the next photo:
A correct 1969 system should look like this:
The fast idle cam is not correct for the 1969 system, and will not work properly with the '69 components:
To work with the other '69 components, it should look like this:
To get the carb off permanent fast idle, they just bent the heck out of the fast idle cam support tang:
It should look like this:
To prevent the mismatched choke parts from interfering with secondary operations, they simply removed the secondary lockout lever. See the photo above of the correct choke setup to see the lever correctly installed:
Pulling the secondary rods out of the carb reveals that the rods are not correct for the carb - they are far too rich. The rods are the cheap brass reproduction rods that the commercial builders use. The correct rod (silver) on the right is what should be in the carb:
Wrong float installed. The commercial builders have a fondness for brass floats. They do not float and perform the same as the correct Nitrofill float, so you cannot be sure what you float level is set to. Bad brass float on left, and correct Nitrofill float on the right:
Here is a serious issue that is very common with the commercial carbs. The commercial builder cut the power piston stop tang off with a pair of sidecutters. This makes the power piston ride WAY too deep, pushing the primary rods all the way down into the jets and running the carb extremely lean. This cannot be fixed - the power piston must be replaced. Cut piston on the left, and a correct piston on the right:
To further aggrevate the power piston issue, they then installed a completely inappropriate power piston spring, just to make sure power piston operation was really screwed up. They must have obtained this spring out of a Bic ball point pen. Bad spring on the left. Correct 7036019 Q-Jet spring on the right:
Here is another favorite "tuning trick" done by the commercial builders: They plug the supplementary idle air holes in the float bowl with either epoxy or lead plugs. This effectively screws up the entire idle air'fuel mixture calibration and control, and also causes a bad rich condition in the transition circuit. Compare the plugged holes to the correct hole configuration in the photo below this:
This is what the hole should look like:
To cause further performance problems, the secondary linkages have been bent and altered. This results in the secondary throttle opening over-center for decreased, turbulent airflow, and prevents full opening of the primaries:
And just to finish off the completely screwed up setup, the primary rods installed were several sizes too lean, and the primary jets were 5 sizes too lean, just to make sure that the carb would run exceptionally bad:
More subtle alterations to the carb include drilled-out air bleeds (both high speed and low speed) and altered Idle Fuel Restrictor tubes.
I am going to use this carb as a weight in the bottom of my trash can. We have found a very nice, original, rebuildable 1969 Corvette carb on eBay for $75, and I'll post up some photos of the rebuild process on this carb later.
Well its a shame what happens to these commercial rebuilds. But its the nature of the documentation (lack of I mean) of the all the variations in the qjets that creates this situation. So many different models of the qjet for car model, year and application let alone for different years. Pretty mind boggling how many different details there are for even same year.
I guess what I'm saying is I congratulate those that can maintain their qjets. I get the feeling an owner should more that a couple ready spares for his car.
Last edited by cardo0; 02-18-2018 at 10:06 PM.
Reason: add: lack of I mean
How much would they make on a carb like that? They have to know that they are screwing someone.
List price on a "remanufactured" Q-Jet like the one I showed above runs around $400 to $500. If I can buy Q-Jet cores for less than $50, I'll bet they're paying less than half that for the carbs they're processing and destroying. So they're making a rather handsome profit on this junk...
Yes, they obviously know they're selling junk. The NAPA store that I have my accounts with will no longer sell "remanufactured" Q-Jets due to the fact that the warranty return rate on them is almost 100%.
I've never seen a commercially "remanufactured" Q-Jet that did not have dozens of problems and issues. I've heard stories of people who have been able to buy a good one, but I've never actually met one of these people. It's a little like Bigfoot sightings.
Lars will you take my carb. Bought it from one of these companies and would prefer to have it corrected if needed before I bring the motor I'm rebuilding to the dyno. Let me know please.
Peter
Lars will you take my carb. Bought it from one of these companies and would prefer to have it corrected if needed before I bring the motor I'm rebuilding to the dyno. Let me know please.
Peter
If you have a commercially rebuilt carb, I'll be glad to put it in my trash can for you along with the one shown above...
Lars rebuilt/repaired my q-jet over 15 years ago. It STILL operates flawlessly today. Best $150 (in 2002) I EVER spent improving the performance in my C3. $50 in parts and $100 in labor.
I still have the file folder (hardcopy) in my C3 repairs documentation.
It wouldn't be a bad idea. Even if it's not a commercially rebuilt carb, there have been a bunch of guys doing funny stuff to it over the past 45 years of its life. I've never seen a carb from any source that didn't have at least a couple of issues that needed to be corrected (with a single exception of a carb that a guy sent to me that had recently been rebuilt by Cliff Ruggles - he didn't tell me it was a Cliff carb, and wanted to see if I'd criticize the setup not knowing where the carb came from - that one carb was perfect - only carb with no issues I've seen in the 800 carbs I've rebuilt over the past 40 years).
If anyone asks you who does your carb work, you can show them that you have all your work "done by a left-handed monkey..."!
I'm always impressed with the dedication of you Canadian Vette owners. Your costs to be involved in this hobby are about twice what people here in the States pay for the same cars, parts, and labor. I receive a remarkable number of carbs for rebuilding and setup from Canada, and round trip postage costs alone run just short of $200. You guys deserve a salute from all of us down here for your enthusiasm alone!
If you have a commercially rebuilt carb, I'll be glad to put it in my trash can for you along with the one shown above...
Lars
Okay I get it. I did go and inspect mine. I purchased is from a place called Monza Carburetor. It looks pretty respectable. So on a serious not, are you willing to inspect and make recommendation if needed.
Okay I get it. I did go and inspect mine. I purchased is from a place called Monza Carburetor. It looks pretty respectable. So on a serious not, are you willing to inspect and make recommendation if needed.
The commercially rebuilt carbs always look very pretty and respectable. Fewer than 50% of them can be saved at any cost, so attempting to save one is high risk at best. I'll be glad to evaluate it and see how bad it is. E-mail me for info, including my terms and conditions on commercial carbs.
These really need to be manufacture theres definitely a market
Always been a holley guy but for a DD Qjet hands down. Drove a 69 rs/ss for years that thing was flawless never touched it.
Edelbrock did offer the Q-Jets as a brand new, reproduction carb for a few years. The carbs were built on the original tooling, and were very good, exact reproductions. They ran very well. However, as with the original Q-Jets, buyers and owners would screw around with them so bad, and blame the carb for all other engine problems, causing warranty issues to be so high that Edelbrock discontinued them. Instead, they are now offering reproductions of the low-performance Carter AFB (aka, Edelbrock "Performer") that nobody screws around with since there's nothing to gain by doing so... Back in the 60's, for a performance upgrade, the first thing you did was throw the AFB (Edelbrock "Performer") in the trash can and install a real carb. How times change...
This is a reman from JEGS which was included in the sale when I bought my 69 350/300 4speed a year ago. The guy had it for years and never did anything with it (thank God!)
Carb # is 7045214 YB 3535 which I think means it is a 1975 M4M for a chevy truck with auto tranny.
Is this good only for a decoy weight or is it salvageable?
Car runs great with its QJet which is a Factory replacement carb #7029207 3226 (for a 1969 350/350 4speed) and has been on the car since the seventies I am sure. (Should I have any problems with it, it will find its way to your shop!)
Just curious if I need to round file the reman carb.
Thanks,
VERYSOON
02-18-2018, 08:35 PM
Photos of Some Problems with Commercially Rebuilt Q-Jet
