They are designed to run a lean cruise - which is a good thing and doesn't impact power. However, they were designed to run lean on 70's gas - pure gasoline. Ethanol requires a more molecules of fuel to maintain a stoichiometric ratio, and on top of that, ethanol has a higher inherent oxygen content which means there is additional air per volume of fuel injected. So it's a double whammy. All of this is coupled with many carburetors being in disrepair or incorrectly built. Imagine how poorly a holley would run if someone set the secondaries up to engage as soon as you touched the throttle, or tried to run without idle bypass air with a big cam.

False on both accounts. Rebuilding a Q-Jet is something most people with mechanical aptitude can learn to do. On top of that, most people just go from a carb in disrepair to some off the shelf Holley because the generic tune in the Holley will run better than an out-of-tune, crudded up Q-Jet.

Absolutely true. There are probably 5 squarebore manifolds to 1 spread bore. And once you exceed about 850 CFM, you'll need to go squarebore or dominator anyways. Going beyond 800CFM is big bucks in a Q-Jet, although going beyond 800CFM is also not all that common for street engines.

Fewer sources, but parts are easy to get.

I am 100% with you on that. I have a local friend who spent big bucks to get a Ram Air QJet to put on his 67 Poncho 400. I spent $45 to buy an M4M core for a friend of his with another 67 400 - which ultimately ended up needing the same amount of parts and work to get to run well.

Q-Jets will work well in high performance applications as well, and you can't beat $FREE if you already have one on your car.

$80 will buy you a fairly rebuild comprehensive kit to get you a QuadraJet that will handle the 500hp Lars mentioned earlier.

If I was building a strip-only vehicle, though, I'd be all up on a Holley (if I wasn't going EFI).

 

Not a fan of the Qjet. I have said this many times: The Q jet is GM's attempt to meter fuel precisely through a carb in the hopes of having to forego first mechanical and later electronic fuel injection for its cars and trucks. The earlier mechanical fuel injection was difficult to tune for performance and was expensive-enter the quadrajet. It was generally a one size fits all carb and is overly complicated for what a carb needs to do and does NOT generally improve mileage much. It is a decent carb when functioning correctly but the complicated (for a carb) mechnicals can make them not worth the trouble other than the carb was stock on many C3's. This holy grail nonsense about the Qjet is amusing….

 

At the risk of beating a dead horse into horseradish, ;

Below is a post that was just posted in another thread where a guy is trying to improve his gas mileage. It is in an 81, but the same principles apply.

I guess my final argument on this boils down to:

"Unless you are like the Grand High Priest Pooh Bah and know how to fiddle and faddle with the Q, it just isn't worth it. Any carb out of the box will perform better than a stock q. And guess what? A whole lot less trouble."

If you want gas mileage, stay stock. Anyone with a 75 thru 81 stocker has a pretty lame sports car by Corvette standards. That would be the primary age of the Q junk.

---Quote (Originally by Patro46)---
Interesting year for fuel mileage issues. I remember this year well. I worked as a line mechanic at Jack Marshall Chevy in Claremore in 81 when the introduction of C.C.C. (Computer Command Control). Looking back, I presume we had to start somewhere, so what better place than to take a Rochester Quadrajet, make a few mods and ad a few solenoids and call it good. Problem is, it wasn't all "that good". Not that it didn't work when properly set up, but we already had issues with the standard non-computer Quadrajets already. Not that either were really bad carburetors, they were just misunderstood by the masses and even earned the phrase "Quadrajunk". This said, when clean (not gunked up) with a PROPERLY adjusted both flavors fared well and delivered decent fuel mileage. Even the original 81 Rochester with it's M/C solenoid and PROPERLY adjusted secondaries carburetors offered decent fuel mileage (tiny primary ventura) and lots of go when a PROPERLY adjusted secondary comes into play. From your description, the first think I'd check is the EGR valve. If that's OK, I'd then check the dwell using a high impedance dwell meter. (Not the timing, but the M/C solenoid). I'd also make note if the hardened steel tamper resistant plugs over the idle air screws have been removed. (Most of the time, the carbs were removed and had a V-notch cut into the edge of the carb base exposing the hardened steel plug). You can also see if the factory cap has been removed allowing adjustment of the MC solenoid. If Bubba EVER got hold of your carb you can bet a T-Bone steak it's off. If your dwell is stuck at 10 deg or lower you found your problem. This was a #1 issue we had, and it continued well past 81 on a LOT of other models. Also, if memory serves me, to set base timing you had to disconnect a lead from the distributor to the ecm before setting the base. A LOT of people would attempt to play with the timing and not disconnect this lead, so the ecm keeps trying to com pensate. In closing, a LOT of people jerked the carb and distributor for a pre 81 distributor and put a Holley and conventional HEI distributor and blocked off the EGR valve, removed the cat and put a test tube in and called it a day. Not that I'm advocating such behavior tho....

Edit... Seems further in the thread you mentioned the computer stuff has been removed and replaced with conventional Quadrajet and distributor. This said, if mechanical issues aren't the case, timing and carburetion are about all that's left. I'd speed the timing up until it clatters, then retard it to just where it doesn't (under hard acceleration) Good Luck!

 

And mine is - 750CFM is 750CFM. Your post illustrates a few of the points I raised. The main one is that you can't compare a 30+ year old carb with 30+ years of idiot mechanics idioting up the carb with one that's been built to spec by a Holley/Edelbrock/Quick Fuel/Demon technician.

The Holley on my Ford F-250 ran like crap compared to the Q-Jet I have now. So by that logic, Q-Jets are better.

The E4ME is an even worse example, because there are archaic computers added to the equation. In working condition, the E4ME actually runs really well.

All of these carbs are also saddled by the late 70's ignition theory (ported timing, next to no mechanical advance, tons of vacuum advance), rudimentary emissions controls (EFE, EGR) puny compression ratios, etc. It's easy to see why the carbs that sit on top of them get a bad rep.

I've torn a Holley (mech sec) to bits and put it back together, and it amazed me at how easy it was to do. A Q-Jet is stressful the first time. After that, I can have it torn down and back together in under an hour.

I will gladly cede that without ever having touched a Holley, I could tear it down and put it back together in about 20 minutes. My first Q-Jet was probably 3-4 hours with a lot of reference material.

But I also prefer my USP, which is mechanically complex but more comfortable in a lot more situations versus a 1911.

 

I love a good challenge, that is why I am rebuilding/upgrading the Q-Jet in my '77. 17057504, I think it is. The good thing is Shark Racer is giving me some hands-on assistance and so far all it has cost me is a pulled chicked sandwich with a side of mac & cheese at the nearby BBQ place.

Going to have to deal with some serious warpage of the air horn and main body though, I am taking a good look at the de-warping method Reelav8tr posted last September.

 

some people are just thin skinned, i wouldn't lose any sleep over it. the entire q jet issue can get heated quickly. much like aluminum radiators

 

I learned all about Q-Jets to get some free BBQ - also because I appreciate the smiles on people's faces when their cars run like scalded apes! I'm also very interested in your build because I was curious how well my motor would do if I'd gone down the path of higher CR - so you're answering that question for me to a degree.

 

Here's my take on the subject. I like to work on my own stuff. I don't understand q-jets so I don't use them. I would learn about them except it seems like a waste of time. Open any aftermarket catalogue and you'll see pages of holley carbs and accompanying goodies to go with them. I'm sure if Lars tuned my q-jet it probably would fly and shoot unicorn farts out the tail pipe but then Lars is doing the work and not me. To come to the end of my mindless ramblings I say use the carburetor your comfortable with.

 

If I was delivered a car w/ a Holley on it, I'd leave the Holley on there.

If I was delivered a car w/ a Carter/Edelbrock on it, BUHBYE. It'd get replaced w/ a Q-Jet merely because I have a small selection of good used cores and a fairly strong understanding of Q-Jets. So, for $80 I could have an excellent running Q-Jet, can't (easily) get a Holley to replace it that cheap. Holleys are easy to work on but frankly I have very little knowledge of tuning Holleys and am way down the field w/ learning Q-Jets.

Lars is a ridiculously great option though... people have paid more to do less, that's for sure.

I agree with your point, though. If it's inside your comfort zone and you're not willing or interested to learn something else (not trying to imply it's a bad thing), I can see sticking with something. I don't know if I'll have an opportunity to learn Holleys, but if I had the opportunity I'd take it. I almost took on an Edelbrock project for someone as well, just to learn.

 

Lemme tell you how true this is:
20 years ago I bought a custom Carb Shop Q-Jet for like $450.
It was NEVER right. Countless things done wrong.

A week with Lars (for pretty-much peanuts) and this thing shreads.
My old 68 L36 is a blast to drive. Don't hit it hard in city streets.