quadrajet questions

I have taken a couple of pictures of the quadrajet carburator which came stock on my 1985 sbc. I am going to use this carb on my roadster pickup, for the sake of economy. This engine came with a ton of "clean air poop" on it, which I have removed and trashed. (sorry to all you tree hugger types). I have plugged all the various vacuum ports on the carb, except the one on the rear side at the base, which will be used to power my distributor vacuum advance pot. The person I bought the car and engine from had added a pull type manual choke to this carb, and I don't know if he removed some linkage or not. I can't figure out what opens the choke plate on the large bore side of the carb. It seems to be spring loaded shut, and although there appears to be a place for a linkage at one end of the butterfly shaft, there is no linkage there. Also, there is a large tube sticking out the front side of the carburator at the top, and I don't know its purpose. Is it a vacuum tube that I can safely plug, or is it some kind of overflow tube for the float chamber? Thanks for any help---Brian

second picture of quadrajet

The Q-jet choke is supposed to be opened by either a vacum pull-off or a heat riser. As for the vacum port, if memory serves me right, that is a secondary vacum port. It *might* be pluggable. However, I would personally make use of it.

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Originally posted by brianrupnow
second picture of quadrajet

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the big tube is a vent that goes to the charcoal canister for the gas vapors. it looks like to me the choke is open, if not the spring in the choke housing reg. it. i think you are taking a pic of the secondary butterflys. the choke butterfly is the small one at the top of the carb. the big betterflys are spring loaded and opens according how much air is pulled across them when you open the carb all the way up. :D

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Originally posted by lt1s10
the big tube is a vent that goes to the charcoal canister for the gas vapors. it looks like to me the choke is open, if not the spring in the choke housing reg. it. i think you are taking a pic of the secondary butterflys. the choke butterfly is the small one at the top of the carb. the big betterflys are spring loaded and opens according how much air is pulled across them when you open the carb all the way up. :D

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i went back and looked that is a manual choke on that carb, and the only rod you would need to make it work is on there, its the little rod going up to the butterflys.

Trash it and get a Edelbrock or a Holley. I would get rid of the quadra-junk, but that's just my opinion.

If the choke(small top plate) is open all the way then when you open the throttle the secondarys(large bottom plates)should open also.

I thought the secondaries were vacuum not mechanical on the quadrajets. The throttlebody is mechanical but the actual secondaries are vacuum. But I could be wrong.

Sometimes I have an amazing capacity to confuse even myself. Thank you for the answers. I will plug the port which vents to the now non existant charcoal canister.. I have done this before with a quadrajet, but it was about 10 years ago and I couldn't remember. There seems to be a whole whack of vacuum ports, both large and small. I plug the small ones with the shank of a wooden match dipped in 2-part epoxy, then pushed into place. It gives a permanent seal, however if you ever do have to open the ports, they are easily drilled out with a small drill bit in the electric drill. For the larger ports I use a peice of wooden pencil dipped in epoxy. This probably sounds crude as Hell, but the roadster I built in 1996 had the same style carburator, plugged the same way, and it ran great. I plan on using the large vacuum port at the rear side of the carb, at the bottom, to run my distributor vacuum advance---is that a good choice? I can't remember what port I used last time. As far as the choke goes, I know that the choke plate on the small bore side of the carb should normally be operated by a bi-metallic spring, but in this case has been modified to be operated by a pull cable. I just couldn't figure out what actuated the choke plate on the large bore side, and I thought maybe there was some external linkage removed. When you buy a used vehicle you are never really sure what may have been done to it by a previous owner.

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Originally posted by randywrench
If the choke(small top plate) is open all the way then when you open the throttle the secondarys(large bottom plates)should open also.

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there is 2 sets of big butterflys, a top and a lower, if you open the throttle wide open then the lower butterflys will open, but the top ones wont unless it is on a motor and the motor is running. air thats pulled in the motor when you open the lower butterflys opens the top ones. if the choke is closed then the lower ones wont open eather :D

I thought the way I put it didn't sound or look right after I posted. Told you I could be wrong.

The top secondary plate is spring loaded shut and when the lower plate opens air flow pulls the top open which controls extra fuel.Smog motors had a vacuum pull off to control when yhe secondarys could open(you don't need it!) The large port in the rear bottom threaded hole, orig was used for power brake vacuum it is supplying full vac. at idle. I put in a 1/4 inch pipe plug and put distributer vac. to the small port right next to the big one

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Originally posted by brianrupnow
Sometimes I have an amazing capacity to confuse even myself. Thank you for the answers. I will plug the port which vents to the now non existant charcoal canister.. I have done this before with a quadrajet, but it was about 10 years ago and I couldn't remember. There seems to be a whole whack of vacuum ports, both large and small. I plug the small ones with the shank of a wooden match dipped in 2-part epoxy, then pushed into place. It gives a permanent seal, however if you ever do have to open the ports, they are easily drilled out with a small drill bit in the electric drill. For the larger ports I use a peice of wooden pencil dipped in epoxy. This probably sounds crude as Hell, but the roadster I built in 1996 had the same style carburator, plugged the same way, and it ran great. I plan on using the large vacuum port at the rear side of the carb, at the bottom, to run my distributor vacuum advance---is that a good choice? I can't remember what port I used last time. As far as the choke goes, I know that the choke plate on the small bore side of the carb should normally be operated by a bi-metallic spring, but in this case has been modified to be operated by a pull cable. I just couldn't figure out what actuated the choke plate on the large bore side, and I thought maybe there was some external linkage removed. When you buy a used vehicle you are never really sure what may have been done to it by a previous owner.

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brianrupnow there is no rod that opens the top back big betterflys. air opens it up. there is a small spring around the top shaft that you can adj. it to make the seconderys open sooner or make it later depending how much secondery carb you wont.

:D

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Originally posted by randywrench
The top secondary plate is spring loaded shut and when the lower plate opens air flow pulls the top open which controls extra fuel.Smog motors had a vacuum pull off to control when yhe secondarys could open(you don't need it!) The large port in the rear bottom threaded hole, orig was used for power brake vacuum it is supplying full vac. at idle. I put in a 1/4 inch pipe plug and put distributer vac. to the small port right next to the big one

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that is what ive been trying to say for the last 20 min. :rolleyes:

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Originally posted by lt1s10
there is 2 sets of big butterflys, a top and a lower, if you open the throttle wide open then the lower butterflys will open, but the top ones wont unless it is on a motor and the motor is running. air thats pulled in the motor when you open the lower butterflys opens the top ones. if the choke is closed then the lower ones wont open eather :D

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Sorry lt1s10 I missed this post!

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Originally posted by randywrench
Sorry lt1s10 I missed this post!

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no problem, he got the same answer from 2 people almost at the same time, so he should belive it. most of the time its 2 people telling 2 dif tails and he wouldnt know what to belive.:D

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Originally posted by DennyW
Heres the front. These are just quick references for you to see.

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looks like youve worked on a few of them to.:D

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Originally posted by DennyW
Hahaha, yes, I have. I work on all kinds. That was one of my main goals. I wanted to learn all I could on all the carbs. I even have the ho-made wrenches for the imports, hahaha. I thought maybe by him seeing some writting on the pictures, it would give him a better idea. That's:)

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thats cool, i went to a few gm schools on them.:D

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Originally posted by DennyW
Cool, me also. I went to each type of carb school. I really enjoyed learning all those things. My favorite one to learn was the older Ford variable vennturi type. I think I was the only one here in my town that did them. Back then, they wanted 800.00 to rebuild them. I charged 500.00. I think I even have a couple of the diaphrams for them, hahaha.

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i messed with them a little but we changed some over to holley. i really didnt know what i was doing.:D

You guys are great! I'm saving this page to my favorites because Brian is always a few months ahead of me, maybe a year! Anyway I also have a Quadrajet I plan to use for a while but my brake booster is just a plastic fitting on the power brake unit while you show a threaded connection at the carb end. What kind of a tube do I need to connect the brake cannister to the carb?

Don Shillady
Retired Scientist/teen rodder

3/8 inch double flared fuel line screws into the fitting that is on the back,bend to fit and then a rubberhose and clamps to plastic check valve on brake booster.