quadrajet on a 250 inline advice
 

as the title states, i picked up an offenhauser 4 barrel intake manifold. and the guy gave me 4 quadrajets to go with the manifold. im kinda new to the carb set up and tuning. i was hoping some input on how to set up a quad to use on my inline. here is what i would like.. reliability out of this set up, better performance , and still have reasonable mileage, i would like to keep the manual choke that i have now.
any advice good or bad is welcome, thanks in advance..

Re: quadrajet on a 250 inline advice
 

You'll need an adaptor from spreadbore to squarebore. Offy carb mount isn't square. Carb needs to be run sideways. Quad too big. Small primaries good though. Manual choke will be fun to set up. You'll need a heat plate to warm up the plenum. Carb linkage could be fun to set up.
Are you running headers too?

Re: quadrajet on a 250 inline advice
 

It came with an adapter so the carb will bolt to the manifold. What size jets should I use ?

At some point I would like to run headers but I don't have them at this time. And I know when I do I will need to use a water heat plate on the intake manifold.
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Re: quadrajet on a 250 inline advice
 

It came with an adapter so the carb will bolt to the manifold. What size jets should I use ?

At some point I would like to run headers but I don't have them at this time. And I know when I do I will need to use a water heat plate on the intake manifold.
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Re: quadrajet on a 250 inline advice
 

Even the smallest Q-jet will be too big for that 250.

I'd look at a Holley 390cfm 4bbl carb.

Gary

Re: quadrajet on a 250 inline advice
 

why couldnt i just put smaller jets in the quadrajet?

Re: quadrajet on a 250 inline advice
 

Google Cliff Ruggles. If its possible, he can point you in the right direction.

Re: quadrajet on a 250 inline advice
 

thanks for the tip oldgold.

i thinks its strange that no one has put a qjet on an inline...

Re: quadrajet on a 250 inline advice
 

does anyone have more info on a holly 390?
or any other carb to use besides a qjet?

Re: quadrajet on a 250 inline advice
 

Hi sixtyeightchevykid,

I disagree about the Quadrajet being too big for your 250. GM used them on smaller engines than that from the factory (231 Buick V6 for example). Their secondary air doors limit the flow based on engine demand. And GM often used a stop/tab to limit the opening of the secondary air doors on carbs used on smaller size engines.

Now, that's not to say that you can bolt any old Q-jet onto your 250, make a few jet changes, and have it running perfectly. There are a HUGE number of different Q-jet calibrations for various engines/vehicles that have different jets, metering rods, power piston springs, air bleed sizes, and more. With that in mind, getting a carb that was originally used on a similar size engine would make the best starting point. It'll still have to be fine tuned for your particular engine/vehicle but it'll be a lot better starting point than a Q-jet originally off a larger engine.

Hooking a manual choke up to a Q-jet isn't that hard. Adapters are readily available to convert the integral hot air or electric chokes to a manual cable. And you can hook the cable directly to the linkage on the divorced choke style carbs ... just have to make a bracket to hold the cable.

For the throttle linkage, I think adapting a cable style setup from a newer truck might make it easier to hook up to the Q-jet or any sideways mounted 4bbl for that matter. You'd likely need a longer cable than stock though.

Re: quadrajet on a 250 inline advice
 

im glad someone is on the same page as me.. but i cant find any info on how to use a qjet on a smaller engine, there is tons and tons of info on what to do to put one on a v8 but nothing on a 6 cyl.

i think the main reason i want a qjet is because i have 2 that i could use, one is off a chevy, the other is off an olds. but im still undecided on what i really want.

Re: quadrajet on a 250 inline advice
 

Believe it or not a quadrajet can be a variable CFM carb. THe smaller engines that used them from the factory had the secondaries limited (the upper air flap) allowing that Q-Jet to be used on many smaller engines.

You can also adjust the upper air flap by strategically drilling and tapping a hole above where the air flap stop rests.

www.cliffshighperfromance.com Cliff is THE Q-Jet answer answer man. I would get the numbers off the 4 carbs you have, to pick the best one.
The numbers are on the drivers side of the carb on a vertical flap on the back barrel of that side of the carb, the # will start w/ a 70 or 170

A smaller 4 Bbl carb might be easier to tune. If you insist on a Q-Jet I'd contact Cliff. Get his book also, it's a must!!!

Just changing jets on one of your Q-Jets isn't something that is an answer to the Q-Jet swap. Q-Jets have primary jets that have metering rods placed in them that control the fuel into the carb. Gaining knowledge of a Q-Jet will help you

Theres a lot of info about Q-Jets on Cliff's website. also..

THe biggest problem w/ running a 4 Bbl carb on a smaller engine, is tuning. Getting the engine to perform properly going from part throttle to full throttle can be a challenge. Probably a reason not a lot of 6 cyl engines got 4 Bbl carbs from the factory.

THe Pontiac overhead cam 5 (it was a Chevy 250 w/ a different head) was an exception, but it was engineered to use the 4 Bbl carb, and was a one off design, that is rare and unusual.

Re: quadrajet on a 250 inline advice
 

i read cliff's book and i didn't find much if any info on using a qjet on a smaller engine. covers rebuilding and modifying for v8s.

the more i read and research i think a qjet will be more hassle and a bigger headache than its worth, so im thinking about going with a 390 holley. the more people i talk to say that the holley will be a better fit for the little engine i have. i looked over the manifold i have more closely and the adapter i have would not work with a qjet.

so the new question is, what will be needed to run a 390 holley on my 250?

Re: quadrajet on a 250 inline advice
 

It's definitely worth the try since you already have the manifold, adapter and carbs. All that can happen is that you will be happy with it or not like it. If not you don't like it's just a matter of reverting back to what you had.

From what I've read... The problem with using a 4 barrel in a six is not that it won't handle the extra carburetion it's the fuel distribution. I'm not an expert on this but what I remember reading is that 3 single barrels work better.

Re: quadrajet on a 250 inline advice
 

68gmsee. i think 3 singles would look good on the engine, but i have had way too many issues with the single barrel carb that it is time to get rid of it,

Re: quadrajet on a 250 inline advice
 

I'd hold on to it anyway. They're easy to repair if they haven't been butchered by previous rebuilders and can be used as a core.

Re: quadrajet on a 250 inline advice
 

i will keep it, just not use it. now im just looking for info on using a holley 390...

Re: quadrajet on a 250 inline advice
 

check out my build, I am going to run a Holley 390 on the Offy 4 barrel manifold.

Re: quadrajet on a 250 inline advice
 

look into the pontiac overhead cam sprint six. it was a chevy six with an overhead cam cyl head and they ran a quadrajet from the factory. My brother owned one, it was a 1968 firebird. it was pretty peppy. the quadrajet was like a 500 cfm or something like that. hope that helps

Re: quadrajet on a 250 inline advice
 

I heard GM Brazil used Q-jets on L6s. Of course they use sugar cane alcohol for fuel there and a much higher CFM is required for pure alco than gasoline.
Santucci's book, "Chevrolet InLine Six Cylinder Power Manual," shows an 'Experimental Chevrolet (never released) four-barrel manifold for Quadrajet carburetor', on page 115.
Personally, I have an Edelbrock 1404, 500 CFM squarebore [AFB clone] on the 4 -hole Offenhauser intake with Clifford headers, on my 292 in my '68 C/10 Stepside. I replaced the '68 rod-and-bellcrank linkage with an aftermarket throttle cable. Much improved.

Re: quadrajet on a 250 inline advice
 

The OHC quadrajets are very specific to that model, with some very uncommon jetting. There is also a Holley repalcement carb for it.
250 will not like the 750 cfm Q jet, period.
Best bet on a basically stock 250 is a Holley 390, or a Holley 2bbl.

Re: quadrajet on a 250 inline advice
 

thank you d13, i have realized that a qjet is too big and wont be worth the time and headache to make it work that is why i have been asking for info and advice on a holley 390...

Re: quadrajet on a 250 inline advice
 

I ran one for about 25 years on a 292 bored .030-over. Sometimes it ran good. I always needed an expert to tune it up. When it backfired I was out $8.50 for a new power valve.
On my last rebuild, I ran the 8007 holley 390 CFM for the first 500 mile break-in, then it blew a power valve, possibly manifold leak-related. I wouldn't set up right. My Holley guy was going thru an extremely painful divorce and so I would up getting the Edelbrock 500 CFM 1404, clone of the Carter AFB. Now a 400 CFM AFB might sound ideal, but no one makes that small an aftermarket carburetor anymore. Because of a demand type secondary, the EDL-1404 only draws in as much air as it needs. QJets do about the same. I never had good luck with the QuardaJet even on V8s.

Re: quadrajet on a 250 inline advice
 

would you recomend aholley 390 for a stock (other than offy intake and langdons headers) 250?

Re: quadrajet on a 250 inline advice
 

Sure. You gotta like tuning Holleys however, and not have any fear that little springs and small parts might go whizzing by your ear. I have heard the power valves in the new ones are protected from backfiring, but I'm not sure. I really liked a 50CC accelerator pump on the 4160-8007. Of course fuel economy went out the window.
I eventually migrated to the Carter AFB design. More user friendly and idiot-proof. Carter got bought out by Federal-Mogul, who eventually dropped selling carburetors, but Edelbrock markets virtually the same carb, just shinier and more bucks. In its day there was a 400 CFM AFB, but that's too small for a HiPo vendor like Edelbrock to make, so we'll never see new ones again. I don't know how good a junkyard find 400 AFB could be, you'd have a hard time getting the small expendable parts like jets, springs, and step-up rods unless they were common to the later AFB/Edelbrock Performer type.
Santucci recommends 500 CFM for the "STD-LD" [standard low deck] or 250, and 600 CFM for the "HD-TD" [heavy duty tall deck] or 292. (His reason for the non-CID based nomenclature is that once serious hot-rodders get busy boring out the cylinders, the displacement is changed. A 292 bored .030-over is actually 296 CID, at .060, its 301 CID. A 250 @ .030 = 254; @ .060 = 258.
The parts guys at the local Chevy dealer told me to just call it a 292, since nobody would know what engine I was talking about if I referred to it by some exotic number.) Personnaly I like 500 CFM for the "296" and 600 CFM for my 350 in the other truck.