Ok, I'm looking to get a q-jet restored cosmetically, and perform flawlessy. I called TA about their service, they want 395. Not bad, but still pricey. I wanted to upgrade to the bigger q-jet, which is supposedly 800 CFM. They want $125 for a core charge.... OUCH :spank: :spank: I have my original 68 430 q-jet, which is either a 725, a 730 or a 750 CFM. Those are teh numbers I've heard. Here are my questions: 1. What size is my Q-jet? I know for a fact that it is the original to the motor. 2. Would there be any benefit to upgrading to the larger q-jet? 3. How can the 2 q-jets be distinguished? Whats the story here? Please help..
So far as I know, and as confirmed in Doug Roe's book (but my copy is very elderly) there are TWO sizes of Q-Jet: 750 and 800cfm. Edelbrock claims 850 for one of their (now discontinued) Q-Jet clones--and I have no idea what the difference is. Smaller CFM ratings--like 650--are 750 carbs that don't open all the way. The 750 has a smaller primary venturi pair than the 800. It's easy to tell the difference when you've seen one of each next to each other. I have seen decent photos of this on the web, possibly on this very site. If I locate them I'll post a link I'd expect yours is a 750. I don't think the 800's were produced until '71 or so. I've been told that the '75 and newer carbs are all 800's, Wrong. I own a newer Q-Jet with the smaller venturis. Then I was told it's all the NON-Chevy Q-Jets, but I'm not buying into that until I see more evidence. Buicks were among the first to adopt the larger carb. Buicks seem to do well with big carbs.
Thanks for the info. I have a 76 Q-jet from a 455, and it appears to be an 800. its very easy to tell the difference. The 76 carb has a extra canister type thing on it. what the heck is it? its built into the carb body and looks like R2D2.Will that peice hurt performance? Thanks for the help...
Your 76 carb is an 800. Your carb also has a lot of pollution control features. You will be better off with a 72-74 carb from a 455. If you don't have a serious street engine, you can use a 750. Contact John Osborne for a performance carb rebuild. He is listed on our site at www.buickperformance.com/vendors.htm For the 750 vs 800 id, visit http://www.buickperformance.com/qjet.html
"The 76 carb has a extra canister type thing on it. what the heck is it? its built into the carb body and looks like R2D2." Are you talking about the phenolic "shot glass" that takes up the space where a very few cars got an aneroid bellows? Nothing to fear there! The '75 and newer (Modified Quadrajet--Mod Quad) has a wonderful adjustable part throttle feature. Knock out the aluminum plug in the air horn, tap for pipe thread, and you have instant access.
Q-jet un-warping tool and throttle shaft bushing kit All Q-jets are warped and have loose throttle shafts, www.mrqjet.com has the only fix. A Q-jet has no chance of working correctly until it is first un-warped and has new bushings.
I must disagree with the statement that ALL are defective. There were quite a few of these carbs damaged by heat, but drawing the conclusion that ALL are defective is a bit of overkill. I have rebuilt quite a few of these units that were assumed to be defective, however, a rebuild or simple repair was all that was necessary to put them back in top shape again. Assuming that the change in idle characteristics when the throttle shaft is sprayed with carb cleaner means that the shaft is leaking may lead to needless and costly work. They all leaked to some degree due to the need for clearance in hot conditions. Even new units will respond to the spraying of carb cleaner on the shafts. Ray
Ray Take a Q-jet that you think is working oK and install our bushing kit, and un-warp it with our tool and I'll bet that you change your mind. After rebuilding more than 1000 q-jets during the past 38 years, I can honestly say that I've never seen even one that this procedure didn't help, or completely change into a very good working unit again.
