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Send me an e-mail request for my "Commercially Rebuilt Carb Problems" paper and I'll send you some info on all the problems you're going to see with that carb. You can then decide which one of your boats needs an anchor...
Check out the continuation of this story when we find a $75 '69 Vette Q-Jet on eBay, rebuild it, and test it to replace the Commercial carb in this thread:
I just don't understand why people over the years think that their shade tree modifications were better than the engineers that designed the Q-jet in the first place. How can these re-manufacturers get away with this crap knowing that they are just masking problems?
I boggles my mind.
Great information as usual Lars.
I have two q-jets. One is on my car and from what I see it appears to be a good stock unit. It runs good right now. The other one is sitting on my bench. It was a reman that I bought shortly after I bought my car. It looks OK but I think I'm going to pull it apart to see if any monkeys have been F&^%ing it. I'm deciding which one to send to the Great and Powerful Lars to work his magic. If my reman one is screwed up I'll have to send the one I'm running now and hopefully it's not modified and can be rebuilt to factory specs.
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
If you are going to junk it just send it my way. I'll pay for shipping and throw you a few bucks so you can get a 6 pack for your trouble.
Jerry
What a great informative thread.....thank you for this as I would not know what is what without an original to compare it with.
I think I am going to try and find one like the E-bay carb your customer found and do one up........been a while. I do vintage bike carbs and many others for customers but have not seen a working Q-jet in almost 20 years......
Hey there Lars,
Been reading your inputs for quite awhile and have a ? for you..
Is there any way or chance of downloading all of your papers in one place???
I am especially interested about the information you offer to prospective site members that want to have you work their quadrajets....
In advance I appreciate your help and concern for the forum members...
mk's78
Mike
Originally Posted by lars
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.
Hey there Lars,
Been reading your inputs for quite awhile and have a ? for you..
Is there any way or chance of downloading all of your papers in one place???
I am especially interested about the information you offer to prospective site members that want to have you work their quadrajets....
In advance I appreciate your help and concern for the forum members...
mk's78
Mike
Glad to see that some of you find the info useful - we don't have a huge following on these Q-Jet threads, but as long as there's some interest in this tech subject I'll keep posting up some info and projects from time to time.
I don't post any of my articles, and those posted by others are outdated and obsolete - I update and revise my articles any time I find new, relevant, accurate information, and the people who are posting my articles never update them. So just drop me an e-mail request for my "Tech Article Listing" and then request the articles you want directly from me. This will assure you have any articles you want, and that the info you're getting is current. From time to time, ask me for the current version of any article and I'll make sure you get the latest info.
I have an entire Tech Sheet on my carb & distributor rebuild & test services - again, just drop me an e-mail request for the info and I'll get it right out to you.
Carbs staged for rebuild and test in my workshop:
The Test Mule engine ready for the next carb test:
As noted, be sure to check out the continuation of this story as we rebuild and test the replacement carb for the one shown in this thread:
Lars, great information as usual.
I just took apart a re-manufactured q-jet that I've had for years and although 3 of the metering rods and the float is brass everything else you point out about bad rebuilds is not there from what this untrained eye can tell. The secondary air holes have never been blocked. Without seeing this carb do you think it would be a good rebuild candidate? I took some pictures if that will help.
How much would they make on a carb like that? They have to know that they are screwing someone.
They make enough to keep doing it....because they can pretty much count on IF you return it for another piece of crap with another list of problems..and do that a few times...you will get sick and tired of it and get one form somewhere else. They are hoping that you will not want full refund.
The PROBLEM is that they do not care.
Heck way back before the internet and all that. Buying rebuilt Quarda-Jets was a crap shoot at best. I remember going through about five or six until I finally got one that I( could adjust the idle mixture screws. Back then...anytime I needed to do major carb work..I just shuddered due to 99% of the time the owner did not want to buy a new one.
They make enough to keep doing it....because they can pretty much count on IF you return it for another piece of crap with another list of problems..and do that a few times...you will get sick and tired of it and get one form somewhere else. They are hoping that you will not want full refund.
The PROBLEM is that they do not care.
Heck way back before the internet and all that. Buying rebuilt Quarda-Jets was a crap shoot at best. I remember going through about five or six until I finally got one that I( could adjust the idle mixture screws. Back then...anytime I needed to do major carb work..I just shuddered due to 99% of the time the owner did not want to buy a new one.
lars...GREAT write up on what you see.
DUB
True statement....in 1996-97, I worked at a NAPA in Troy,MI and we quit selling rebuilt carbs period because of outfits like Tomco and such....was not worth the hassle.
I feel that it is time that Q-Jets get some support and thanks for coming back Lars....they really are a great mixer and they fit vintage stock equipment....
Well, aren't you the smart one, Jeff... I had just finished testing a carb and shooting photos of the test run when I removed the carb and pulled the fuel tank to go get it filled. The fuel tank is at my feet as I'm shooting that photo...
But just so you don't worry about me not having a fuel supply, here it is:
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!
Lars
Take off, Eh!!!!
Keep up the great works Lars, bringing back one Q-Jet at a time!!!
Sorry to hijack, but you guys know these carbs better than anyone! Here is a new-to-me Quadrajet that's attached to a mildly modded 72 base Vette. It runs like a raped ape, but its a little hard to start from cold. Im wondering if the choke mechanism looks right to your experts. Let me know what you think? What carb do I have here? Yeah, Bubba's clearly been at it plugging the hoses with those go-fast bolts! lol. This is exactly as found, havent touched anything yet. Anyway....
That's a hacked-up, commercially rebuilt Buick carb (1974 455) with a 90-degree fitting stuffed in the inlet so the Chevy fuel line can be hooked up (Buick float bowl with a Chevy airhorn - what we call a "mix-n-match" carb). The choke isn't hooked up at all - the entire choke coil and connecting rod is missing - the choke is inoperable. That's not going to run very well when cold...
Glad to see that some of you find the info useful - we don't have a huge following on these Q-Jet threads, but as long as there's some interest in this tech subject I'll keep posting up some info and projects from time to time.
I don't post any of my articles, and those posted by others are outdated and obsolete - I update and revise my articles any time I find new, relevant, accurate information, and the people who are posting my articles never update them. So just drop me an e-mail request for my "Tech Article Listing" and then request the articles you want directly from me. This will assure you have any articles you want, and that the info you're getting is current. From time to time, ask me for the current version of any article and I'll make sure you get the latest info.
I have an entire Tech Sheet on my carb & distributor rebuild & test services - again, just drop me an e-mail request for the info and I'll get it right out to you.
Carbs staged for rebuild and test in my workshop:
The Test Mule engine ready for the next carb test:
As noted, be sure to check out the continuation of this story as we rebuild and test the replacement carb for the one shown in this thread:
Ever considered shooting a vid of a q jet rebuild, how to identify what model what to look out for when purchasing one. I had a q jet on my 79 when I bought it. Not knowing better at that time, I removed it and replaced it with an Edelbrock (carter AFB) I now have a Mighty Demon carb on my engine now. I gave my q jet to an instructor when I was in auto tech school I should have known something was up when his face lit up. Shooting a vid may increase the following of Q jet threads.
That's a hacked-up, commercially rebuilt Buick carb (455) with a 90-degree fitting stuffed in the inlet so the Chevy fuel line can be hooked up (Buick float bowl with a Chevy airhorn - what we call a "mix-n-match" carb). The choke isn't hooked up at all - the entire choke coil and connecting rod is missing - the choke is inoperable. That's not going to run very well when cold...
Lars
Hahah, thanks Lars! Yeah I figured something was wrong here. I'll swap it out for a better carb. Thanks!
02-21-2018, 03:31 PM
I should have known something was up when his face lit up. Shooting a vid may increase the following of Q jet threads.