I have a 74 L-82. It need the carb. work. Should i put a holley on it or rebuild the rochester? pro/cons? thanks.....

 

Is the car stock? The quad. is a good carb if you build it right, and it can perform really well. If my '74 had the stock quad, I would've got it rebuilt, but it has a '72 truck carb. I think I'm just gonna go ahead and try the SummitRacing carb and see how it works.

 

Research the archives for some of Lars' papers, along with a carb manual, you'll be surprised that you can rebuild your own carb. Also, if you know what your carb isn't doing right, it'll help you know what to look for. Plus, it's kinda fun, you can say you did it yourself, and you have nothing to lose save the cost of a rebuild kit. Give it a shot...

 

Kind of depends on what the problem is with the carb. If there is a hole in the side, then buy a replacement. If it is just running rough, then try rebuilding it, especially if the carb is original (Lars papers are great for this). Make sure you replace the float.

If your rebuild did not work, and it is the original carb, have it professionally rebuilt if you do not mind spending the money. If you want to save some money, put the original carb on the shelf for the next owner, buy a used Holley 4165 6210 off ebay, rebuild it yourself, and enjoy the manual secondaries.

I know qjets have manual secondaries, but they are effectively vacuum delayed. You will feel the difference.

If it is non-original than I would still try to rebuild it first (unless it is a bullet hole type problem), then look at the Holley. A rebuild kit is a whole lot cheaper than even a used Holley. Plus the rebuild kit for a 4165 is about twice as much as the one for the qjet.

I have run two qjets and two (one totally wrong that came with the car) Holleys on my '74 BB, and I really prefer the Holley.

One caveat: If your vette is an automatic, I am not sure how your transmission will react to the sudden boost from the secondaries. Mine is a manual, and it just chirps the tires.

 

A properly rebuilt Qjet will get slightly better mpg and drivability and run a bit faster than a Holley. The key is getting the Quadrajet dialed in correctly. The Holley will be slightly easier to tune.

 

I have the stock Qjet and it seems to run great, although I can't hear my secondaries kicking in. I had an old cutlass and when you romped on it you could hear the secondaries opening up.

 

Your secondaries aren't 'kicking in' if you don't hear them. Check out the movement of the linkage when you fully depress the accel pedal. Moving the carb linkage by hand does NOT demonstrate how it works when you drive it. The linkage could be mis-adjusted or the carpet/floormat could be too thick. The Q-Jet secondaries are only activated with the last little bit of movement in the throttle linkage. There is also a secondary release on the right side (with the choke) that must be in the correct position (choke full OFF) for the secondaries to be released. The Chevrolet Chassis Service Manual has detailed procedures to properly set-up and check-out the Q-Jet carb. And, YES, you want to keep that carb if it is at all servicable. For many reasons, that carb is a much better choice than a Holley for a street-use vehicle.

 

the motor is stock and have auto trans. i believe it is the the original carb. just bought the vette month ago. The lady had the idle set really high to keep it running. Its been to dam cool out to be working on it right know....lol ..can't wait for spring. thanks for the commnets...

 

Post carb. number, on drivers side of main body. Or search Qjet numbers and you can tell if it proper carb. for car. mds...

 

If you don't get it fixed and just replace it, let me know. I'm looking for a Qjet that fits '73 and '74 350 with auto.
vagabondslr42@aol.com

 

For a stock to mild build driver the QJet is hard to beat.

 

The Q-Jet is a great carb, flows 750 cfm. Rebuild is not hard. Just keep some bowls handy for soaking & cleaning the parts. Take pics for reference as you take it apart.
What are the symptoms besides a high idle? Do the secondaries open?
Good luck, Glenn

 

Thanks, I will check it this weekend after I put in my recurve kit.

 

PowerBlock TV did an episode of MuscleCars that focused on rebuilding a Q-Jet (sorry, the PowerBlock TV site is down, otherwise I'd give you the URL). The Q-Jet is a damned good carb that is a good match for the Chevy SB and BB. Rebuilding them isn't difficult and has a high success rate as long as the base plate hasn't cracked d/t overheating or being torqued down too tight.

Good luck in getting your Vette running right for Car Show season.

 

What size is the air cleaner cover? 12" or 14" For a 74 l-82
Got the base and top ring and seal and a lid but the guy wasn't sure if i the lid was the right one.. Got it for 20$. need to blasted and paint it...

 

Holley or Q-Jet....?
Here's something to consider:
I just finished doing back-to-back dyno testing yesterday on 2 different engines and 4 different carbs, including a Holley (not a cheap one) and a Rochester of the same cfm rating (800). After optimizing those 2 carbs on the same engine, the Holley produced 451 hp and the Q-Jet produced 447.... but the Q-Jet put out 95 more ft-lbs of torque than the Holley below 3500 rpm, which means the Q-Jet will jerk your head off compared to the Holley (501 ft-lbs torque for the Q-Jet from 2500-3500 rpm, with the Holley barely pulling over 400 in the same rpm range and with both carbs producing exactly the same A/F readings), especially if it's installed on an automatic car.

So get rid of that stinkin' Q-Jet and slap a cheap Holley on it.

 

WOW! What a difference! Is that because the Q-Jet does a better job of regulating flow in that lower rpm range?

 

That is amazing. Looking forward to the answer of why.

An aside: Yesterday I filled my first full (non-tinkering around) tank after switching to the 4165 from the qjet. My mileage went from an absolutely crappy 10mpg with the qjet to just over a pathetic 8mpg with the Holley. I may have been flogging it a little more with the Holley, but not much.

Not sure anyone drives these cars enough to care about mpg, but more data is better.

 

The Q-Jet has triple-booster venturies on the primary side, along with a very precise metering system on the primaries, resulting in great fuel metering and fuel atomization, along with outstanding flow velocity, in the low and mid-rpm ranges. The secondary side is more like a toilet bowl, but it still works pretty good, being within 4hp of the Holley on the top end. For a street-driven car with an automatic, the Q-Jet is actually pretty tough to beat... if it's set up right.

You have problems... a correctly set up Q-Jet will easily produce mileage in the high teens on a smallblock Vette. You either have timing that's way off, carb way out of whack, or a combination of both. 8-10 mpg is in the Peterbuilt Semi-truck range...

Lars

 

Thank you for the explanation. The pumps on the Holley gave me the impression that the primaries and secondaries are toilet bowls.

What did the peak torque numbers for the different carbs end up at? I am assuming this was done on the small block you posted pictures of awhile back? If you are going to produce one of your papers with the data and results, please let the forum know so we can send requests.

I am disappointed with my mileage. The car is an LS4, but I should not be getting motorhome mileage. The majority of my driving is on a five mile test loop, and though there are 4 stop signs/lights, almost half of it is 65mph. I would be happy with low teens. Most likely it is a combination of my questionable rebuild skills and heavy foot, but since I only go through about a tank a month I am not going to spend too much time chasing down mileage. The car runs really smooth and strong even if the mileage doesn't show it.

I would chase down 100ft/lbs however.