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Hi,
Just a quick general question - would 4 barrel quadrajets off a mid to late 70's or even 80's GM car fit a 1971 Cutlass? I have been looking for one and a guy near by has a couple. They have the same style choke and the fuel line centered on the front but he isnt sure what they are off of.
I have asked for the serial numbers off them, but just want to be sure if they are from a different year, or even off something other than an Oldsmobile they will still work as long as choke and fuel lines are the same.
Ok, so no serial numbers (yet) but did get some pictures. He says one is manual choke so it's out, but the other looks to have the same choke connections. But, it also seems to have a vacuum canister behind the choke that mine doesnt have as well as a capped port at the bottom back of the carb that mine doesnt have. Looks like the throttle linkage is a little different. Just want to know if any of the things make it incompatible. First pics below are what mine looks like, next are the ones for sale.
Last edited by 71OldsCut; June 26th, 2020 at 04:53 PM.
Hi,
Just a quick general question - would 4 barrel quadrajets off a mid to late 70's or even 80's GM car fit a 1971 Cutlass? I have been looking for one and a guy near by has a couple. They have the same style choke and the fuel line centered on the front but he isnt sure what they are off of.
I have asked for the serial numbers off them, but just want to be sure if they are from a different year, or even off something other than an Oldsmobile they will still work as long as choke and fuel lines are the same.
Will they bolt up? Yes. Do you want to use them? Not so much. While the bolt pattern is the same, that's about all. The throttle arm, fuel inlet, jetting, choke connection, vacuum connections, etc, etc vary from year-to-year and engine-to-engine. Of course, jetting was geared for emissions from the early 70s onward. The 1980s computer controlled Qjets require the ECU and full CCC computer system to operate correctly. If you know what you're doing and can properly jet a Qjet for a non-original application, then the 800 CFM versions from the late 70s are the way to go. If you run screaming at the thought of opening up a Qjet, stick with the original one.
Do you have a carburetor now ? If so what is wrong with it ? If you dont have one at all how about some details on your engine ? Stock ? Modified ?
Like Joe said there are a lot of variables. If you dont have a carb at all you would be much better off having one built to meet your engine specifications.
You're looking for a Model Number not a Serial Number, perhaps moot point. None-the-less, zooming in on your image it appears that one carburetor is Model Number 7041250?
Joe's advice is spot-on. I have a '71 CS 350 sbo engine. I have a '71 CS 455 bbo carburetor on my 350 sbo engine & it's tuned like a champion - thank you very much.
If that carburetor in your 2nd picture is in fact the carburetor you want to use, & it has Model Number 7041250 stamped into the carburetor (which the zoomed image demonstrates), that is a 1971 Oldsmobile sbo engine Rochester Quadrajet 4bbl carburetor. I'm kind of having a hard time determining which of the pictures you're questioning. At any rate, my carb is from a 71 455 (7041251) the 71 4bbl for a 350 would be 7041250.
Correct, the first two are of the one I have now. I was just wondering if I could venture outside of one specifically that came on this car or if best to stick with it. Where I live things like this are hard to come by. Just looking for something cheap to do a first full rebuild on.
I see. Well, let me say this. There is absolutely nothing mysterious about the innards of a Rochester Quadrajet carburetor. There are complete tear-down, reassembly, rebuild videos all over YouTube. If you're only looking to try your skills/attempts at rebuilding a Quadrajet (an admirable way to learn - kudos), buy any cheap-o you can find, order a rebuild kit and Bob's Your Uncle! Have at it. Who cares if it fits or not - it's called a dry-run.
Fair point. If I get desperate I might just do that. I was just hoping when it was done to be able to install it on the car and see how it works.... or doesnt depending on my work, lol. I will keep looking and see how it goes
I was just wondering if I could venture outside of one specifically that came on this car or if best to stick with it. Where I live things like this are hard to come by. Just looking for something cheap to do a first full rebuild on.
Follow Joe's advice. Stick with the model year carburetor application - best. "IF" after you've completed a "dry-run" on a cheap-o Quadrajet and Joe's statement
If you run screaming at the thought of opening up a Qjet, stick with the original one.
still applies, stick with the original. If you feel you've mastered the Quadrajet, nothing ventured nothing gained go for it.
Back when I was a teenager in high school driving a 1970 Cutlass Supreme I thought QuadraJets had some "magic" inside them. I finally got the nerve to do a rebuild (had no other option) and discovered there wasn't anything "magical" about it, just straight-forward automotive engineering. So if a clueless high school kid from last century could rebuild a QJet successfully I am sure with all the internet help available today that you can do it as well.
Be bold, be brave, be informed, and rebuild that carburetor!
I like the '77-'80 BOP carbs, front inlet electric choke. Beware of any Quadrajet, they were emissions calibrated carbs and need the idle circuits reworked and mains re-jetted on modified motors or with use of ethanol added fuel.
The castings and float arrangement are much better on the newer carbs. The electric chokes are nice. The 17080270 is off the Pontiac 301 and is very lean and the secondary air valve (top flap) is actually restricted from opening fully. I you use this carb I suggest reading Cliff Ruggles book and contact him for a correct rebuild kit. Here's a post from his forum page about your exact same carb. https://cliffshighperformance.com/si...p?topic=1974.0
I have a similar carb as the mentioned Pontiac carb, a 83 Canadian spec 307 carb. It is even leaner calibrated than the late 70's carb, idle screw is cranked way up on my mild 350 and also had the air door restricted. The secondary air door took 5 minutes to open fully. The idle passages with need enlarged and probably larger primary main jets to run properly. I also add a threaded cover in place of the aluminum plug and slot the APT adjustment screw on later carbs. Basically you can set a fun tire spinning mixture or a lean fuel economy mixture in minutes. Ken at Everyday Performance did the custom tune on my 79 403 carb, idles much smoother, slightly rich now if anything. Spraying carb cleaner at idle would up the rpm a bunch with factory calibration, now it nearly stalls out as soon as you spray it. The best mixture screw setting is 2 or 3 turns out, not 5 to 6 on the super lean factory calibration. As said Rochester improved these carbs right till the end of production but emissions got tighter and tighter. I actually had a part throttle lean stumble on another 83 307 carb probably because it had the EGR removed and was calibrated for it. Adjusting the APT eliminated it. The extra 50 cfm on the primary side helps performance, it will out perform your current carb IF tuned to your motor.
Last edited by olds 307 and 403; June 28th, 2020 at 05:53 AM.
I actually have a 7041250 from Ken. For whatever reason I just could not get it to work right, or at least better than what came on the car. It is likley just me not being able to tune it in right, but there really isnt that much to adjust so who knows. Either way, through it all Ken was more than willing to answer questions and try to help as best he could.
Hot idle compensator. As the underhood air gets hot, it becomes less dense, which can upset the idle mixture and cause the carb to load up. The hot idle compensator has a bimetallic spring that opens up a small passage to admit more air at idle when temps are hot. By the way, the Chassis Service Manual has a very detailed explanation of how all the parts of the Qjet work.
June 26th, 2020, 04:26 PM
