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post #1 of (permalink) Old 11-16-2002, 02:38 PM
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what carb to use?

I have a 78 chevy 1/2 ton. It has a 350, with a quadrajet carb. The thing runs like crap. The choke sticks, the throttle sticks, it runs rich, it likes to stall, etc... I'm thinking about replacing it, and i'm wondering what i can buy that will give me decent performance at a cheap price. Cheap is a priority.

Any input?
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post #2 of (permalink) Old 11-16-2002, 05:54 PM
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Re: what carb to use?

one of the best and cheapest things to do is rebuild your Quadrajet. When tuned properly they run very well off-road, and handle angles very well.

Tom
post #3 of (permalink) Old 11-16-2002, 06:18 PM
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Re: what carb to use?

Find someone to rebuild you quadrajet. This is the most underestimated carb out there. It will preform as good as any Holly or Edelbrock if tuned properly. The problem is most poeple dont know how to rebuild them properly.

Search www.hotrodarchives.com for an article about Jet Preformance (Jet something I think its preformance) they are top notch when it comes to q-jets, and can build and tune it off the motor if you give them an acurate discription of your motor.

If you don't have the big carb (850CFM) then you might want to get one off a big block 1 ton (I think about 74 or 75) from a salvage yard and send it to Jet. (This info should also be in the same article or one within a couple of months, if you have trouble finding it then pm me and I will search through my old Hot Rods)

The good thing about a q-jet is it will only suck as much air as the motor needs, so if jetted properly you can use one carb as you modify your motor. It also provides fuel milage better than a two berral if you stay out of the secondaries since the primaries are smaller than a two barrel.

If you're mechanicly inclined you can get a rebuild kit for about $30. Also get about three cans of carb cleaner, 1/2 gal of gasoline, something to soak the carb in the gas in, and just to be safe a new float. The rebuild kit will come with instructions to put it back together and do a basic tune so you can get it running again.

After you rebuild it and get it running you can post here again and we might be able to help you get it tuned better.
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post #4 of (permalink) Old 11-16-2002, 08:39 PM
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Re: what carb to use?

I already rebuilt it. I don't know which one it is offhand, i think it's a rochester m4mc. Whatever came stock on a 78 400 small block (thats what the truck had stock). I bought a rebuild kit and went through it, cleaned it up good, put it back together with all new gaskets, and it still runs like crap. it runs a little better now, it's acceptable if it's warm. But when you come to a stop you have to floor it for a second to get it to come off choke and to get the idle to drop down. It's kind of a PITA.

How much would that cost, to send the carb to jet and get it done up nice? And if i were to go with an edelbrock, what would be a good choice? I think the motor has a cam in it and it may be bored 30 over. That's what the previous owner said the previous owner told him, so... All i know is it's a small block with headers. And i don't plan on doing any modifications to it. It's my beater, any serious money will go into my other car first.

Thanks for the help.
post #5 of (permalink) Old 11-16-2002, 08:43 PM
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Re: what carb to use?

Rebuild the one you've got. They are pretty good carburetors when they're tuned. I like them better than Holley and Carter AFB.

There were two versions, the 625cfm and the 650cfm (big block). Some people say there was an 850. I'd like to see proof of such a thing. There was also the APT and non-APT ones. The APT ones appeared in 1975 and can be spotted by the little dome thing on the top near the right front. The best ones are from the late sixties to early seventies. They had the highest CFM (secondary butterfly was already set to open all the way without modification) and were non-APT while usually having a large floatbowl. Also, I'm pretty sure all the APT carburetors had sealed primaries. That means you'd have to modify them (drill holes) to tune the primaries.

You can buy a rebuild kit and a book to teach you how to rebuild the carburetor and tune it for $75 or so from Summit.

If you buy a carburetor, buy a new one from Edelbrock or even buy an abhored Holley. One of those remanufactured and/or rebuilt ones aren't worth their scrap aluminum. They usually drill holes and resleeve things and just plain butcher the carburetor. Usually you can't tune them. The $50 you save by buying a "remanufactured" one from Jet isn't worth the nightmare and the "you never know what you're going to get". Never, ever, buy a "rebuilt" or "remanufactured" one from an auto parts store. Chances are it'll be a piece of [bleep].
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post #6 of (permalink) Old 11-16-2002, 09:56 PM
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Re: what carb to use?

Heres a link to an article on q-jets
http://www.hotrod.com
Its not the one I was looking for but It sais basicly the same thing.

As for an 850 Rochester try
www.jetchip.com
Ok, all they list is the 800CFM but trust me there is an 850 and if I was motivated enough to look I would go out an open my hood to get the #. But, I don't know where my flashlight is and alcohal and hights dont mix well.
post #7 of (permalink) Old 11-16-2002, 10:07 PM
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Re: what carb to use?

Oh yeah, as far as Jet Prefomance drilling and sleaving carbs this is done to IMPROVE flow and most of it would be done to a new carb.

As far as cost I have no clue but I know someone in Tulsa, OK who can rebuild one to a level just below Jet for $50 + parts. Or you could bring it to me in Little Rock, AR and I can do good enough to get it running.

But my guess is if you already rebuilt it you either have the float set wrong or your problem is in the ignition not the fuel system. How old are your plugs and wires? Cap and rotor? Are your plug wires burnt?
post #8 of (permalink) Old 11-16-2002, 11:01 PM
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Re: what carb to use?

plugs and wires are new since i got the truck six months ago. From the symptoms i'm getting i'd definitely say it's a fuel problem. It smells like it's running rich. And the idle keeps getting stuck at like 2 grand. Not good when you want to stop the thing with stock brakes and 35's. I don't think that's an ignition problem.

If i can get the one i have redone right for cheap, that's the way to go. I'm too young to know how to f with a carb, all the other cars i've owned were fuel injected. Well, there was that bike, 4 seperate carbs, none of which worked right, but those were a completely different setup, and i never got those to 100% anyway.

Priorities here are cheap and runs good. Thanks for the advice. Any more suggestions would be much appreciated.

dave
post #9 of (permalink) Old 11-24-2002, 07:55 PM
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Re: what carb to use?

I don't mean to but in, but the Q-Jet is a super carb. I have a Holley for my Jimmy and the Q-Jet that came with it. The Holley is in the garage. Buy the HP Books Rochester Carbs book and study it. There are numerous sites on the internet that talk about the Q-Jet and how good it is. It is the best off road carb (except maybe for the new Holley Truck Avenger) you can get. Go to junk yards and buy old ones and rebuild them and for less than $50 you got a new carb. I have rejetted mine and rebuilt it many times, I still love it.

Good luck,

Jim
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