W-27

I have a 455 engine in my 68 442 which was a dealer installed 68 engine but I just looked at the Rochester QuadroJet and it's a 7042250-0482C which indicates that it's a 1972 350 4 barrel carburetor. It would seem that there is a better application for this motor but I do not know what it is. 7028252 (68 Toronado 455) or 7028251 (68 Hurst 455). I can provide the intake number and engine number if necessary.

dnmfranco

8251 is what it would have came with far as originality
8252 is a good carb ran one on my ram rod before putting original back on and it ran great w it.
So I guess depends on how original you want to go

W-27

My concern is not originality but correct performance. Is a QuadroJet made for a 350 motor going to perform as well for a 455?

dnmfranco

The jets are smaller in the 250's I believe thus a 251 or 252 would serve that motor better.
If you wanted to go a different year and didn't care 9253 is what I run on my 68 442 and runs great

Magna86

Or you could rebuilt the carb with the larger jets etc to perform better with the 455

Gary M

From what I understand they are both the same body but the jets are different. Some say the 250 is auto and 251 is stick. A good rebuilder with experience will get you where you need to be. Me, I'm a newbie but others here will put you where you need to be.

nsnarsk65cutlass

Probably,but the 350 carb may get a LITTLE better gas milage.

wmachine

Most of the differences in these carbs are the jets and other minor things like the power piston springs. You don't need to change the carb, you just need to make sure you have the right internals. As long as the fit, choke, attachments, etc are the same (or usable), then get the right internals.
1. Even if you get the right numbered carb, you can't be sure the internals are correct.
2. If your engine in not bone stock, then things like the power piston spring need to be matched to the engine setup anyway, meaning the correct carb for the stock engine may not work right for the modified version.

hookem horns

68 and 72 used different choke set ups, so how is yours done now? The 72 is easy to swap to an electric choke, and with the right jets would be good to go unless true originality is critical to you.

wmachine

Exactly. That's part of the "fit" I referred to. If you want to stay with the original divorced choke, you need a carb before '70. But since you have a '72 already, I'm guessing you already have an electronic choke.

W-27

No electronic choke on it as the motor is a 68 just carb is 72.

pcard

If it is not giving you trouble and it is working with your current choke and vacuum setup, then keep the carb. Drop Cliff Ruggles an email and tell him your setup. He will advise on your jets, rods, piston springs etc.. That carb's internals may already have been changed for your engine, so take a look inside first for your jet and rod specs so you can give that information to Cliff.
While it is off I recommend you replace the acceleration pump with a new one from Cliff; they are good for today's fuel.

Koda

I think the only real differences in the non-changeable stuff is whether it's a 750 or an 850 cfm, I think. Oh, and choke type, and e-qjet.

W-27

Car is hard to start when with cold engine and idle will not set properly but that could be something else as well.

Fun71

Sounds like a choke issue, which is understandable as your intake manifold is set up for a divorced choke and your carb is set up for an integral choke, so I am guessing you have no choke. Simplest thing to do is swap the hot air choke cover for an electric choke cover and connect it to a switched 12 Volt source.

olds 307 and 403

X2. Block off the little hole behind the choke coil with epoxy, could give a vacuum leak. I always convert my hot air choke to electric.

W-27

Great idea because when I take the intake manifold off i can block the two center passages with stainless steel plates for better gas mileage but that's not until I rebuild the engine.

Fun71

That "vacuum leak" is there with a functional hot air choke so it won't do any harm with an electric choke.

I used a tube thread cap to cover the hot air port on mine in case I ever go back to the hot air coil. Epoxy seems too permanent to me.

Fun71

I don't understand how that will increase gas mileage. The reduction in carb heating will decrease the fuel vaporization, which would decrease mileage, but increase power.

johnnyjaws

I buy that carb from u if ur selling it I need that one

W-27

If I new for sure that the 7028251 would accept the electric choke I would swap even providing it didn't need rebuilding,

W-27

That makes more sense and keeps you "flexible" but I still cant figure out were this "vacuum leak" is but a good picture of it would work.

wmachine

I may have a 7041250 ('71 350) if anyone is interested.

Fun71

The integral hot air choke has a U shaped tube that goes into the exhaust crossover in the intake manifold. One end of the tube connects to the air cleaner housing and the other end connects to the side of the choke housing on the carb. There's a small orifice in the choke hosing so that filtered air can be pulled in from the air cleaner housing, through the U tube (where it is heated), and across the thermostatic coil in the choke housing. The orifice is located in one of the long posts between the choke housing and the side of the carb.

Well, that carb's divorced choke should match up with your intake so you wouldn't need an electric conversion - just hook up the hot air choke.

W-27

My choke doesn't have the U shaped tube that goes into the manifold. My choke just as one bolt on the back of it that bolts it down to the manifold.

Fun71

Right, that is the divorced choke that was used on your '68 engine.
The U shaped tube is used on the '70 and up carbs with integrated choke.
You said you had a '72 QJet, so it should have the integrated choke housing that goes with an intake manifold with the U tube.
If you use your original carb, it should match the divorced choke on your intake manifold.

pcard

Post a few photos of your setup.

allyolds68

I have the same carb on my 70 455. It was a newly rebuilt when I bought it but it was done twenty years ago and shelved. Nothing was good for ethanol fuel so I bought the rebuild kit from Cliff Ruggles. It ran so lean at WOT that it pinged. I talked to Cliff and he recommend changing out the secondary rods to richen it up. I did that and increased the secondary air door tension and now it runs great. I think you can make it work fine with a little tweaking. I changed to CG secondary hanger rods. They are very similar in size to the 68 stock hanger rods which I think are AU's. If your 72 carb is still stock it has CV's which are much thicker than the CG's, letting less fuel in. I also converted the carb to electric choke which is easy

joe_padavano

Let's back up. The FIRST question to ask is WHICH intake is on the 455? If it's a true 1968 intake with a pocket for the divorced choke coil, you cannot easily hook up the hot air choke from a 1970-later carb. If the intake is an 1970-later (or aftermarket) intake with the hot air tubes for the integral choke, you cannot use the "correct" 1968 carb. Figure out which setup you have before worrying about carb numbers.

Second, as Kurt has pointed out, the carb number is irrelevant. Simply change the jets, metering rods, and power piston spring and you have the "correct" carb. Of course, since that engine isn't original to that car, you don't really know what was done to it and if the "correct" carb jetting is even appropriate for your particular vehicle. This is where knowledge of carb tuning is needed to properly dial in the carb. The good news is that the Qjet is flexible enough that even a 350 carb will run acceptably.

W-27

Joe, I totally agree and it is a 68 intake w/pocket so the hot air tubes are out of the question but would an after market electric choke fit and work on it and what are the pros and cons?

joe_padavano

Actually, there are no cons. You can use a stock electric choke in any Qjet with an integral choke housing (like the one you presumably have now). Simply get an electric choke coil from a factory application. I like to use the one for a mid-1980s Chevy big block pickup - Standard Motor Products P/N CV329. Wire it as described in this thread.

W-27

W-27

Today I called Cliff Ruggles (he wrote the book on QuadraJet's) and after I described to him my situation and described the carburetor he told me that its a "remanufactured" carburetor on which the electric choke was taken off and replaced with a divorced choke so that it could be sold as a "68" carburetor instead of a "72" carburetor and they are so poorly "remanufactured" that he wont even "touch it". Well I will scout for a 7028251 or 7028252 then "rebuild it" using Cliffs kit. The present carburetor still works but it's hard to start cold.

wmachine

That's exactly what I'm doing to match a carb to '68 442 stick specs. I'm starting with a 7028252.

You'll probably be better off with the larger (.072) jets. I'm also going with a larger .145 needle and seat that was suggested to me.
The best power piston spring to use will depend on what vacuum you're pulling.
These are the kinds of tuning and tweaks that a good carb re-builder knows how to do.
(Note I am *not* a "good carb re-builder", I'm just someone who has gone though the particulars for the '68 400 carbs)

Octania

I can get '8252 or '9252 carbs in pretty good condition for not too much $.

dnmfranco

Chris how much for 8252 Ty dean