Rochester Quadrajet Woes

KevinP said:

Thanks. I'll look into this. I bought a rebuild kit already, but I'd hate to find that out once everything has already been disassembled! Since you have already completed the process of changing to electric choke, is there anything that needs to be blocked off or redone vacuum-wise when switching to an electric choke version, or do just need to wire up the electric choke to a ground plus a key-on power wire and then install everything else normally? I thought about upgrading to one with electric choke, but I don't want to make things worse by getting it wrong.

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The electric choke conversion for your Q-jet just replaces the thermostat bolted to the manifold with an electric one. You don't actually change anything on the carb itself.

https://quadrajetpower.com/electric-choke-conversion-kit-chevrolet-350-400-71-78/

KevinP said:

Thanks. I'll look into this. I bought a rebuild kit already, but I'd hate to find that out once everything has already been disassembled! Since you have already completed the process of changing to electric choke, is there anything that needs to be blocked off or redone vacuum-wise when switching to an electric choke version, or do just need to wire up the electric choke to a ground plus a key-on power wire and then install everything else normally? I thought about upgrading to one with electric choke, but I don't want to make things worse by getting it wrong.

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I just did this last week on my '77. You are correct, there is a ground wire and a power wire, which was recommended to connect to the wiper motor wire. And of course the electric choke itself which mounts to the manifold. Nothing needs to be changed vacuum wise. I had been having choke problems with the divorced choke thermostat even after replacing it with a new part. The electric conversion seems to be working much better.

If, after you've sorted everything else out, you still want to buy a new carb...check out carburetors unlimited in Peoria, AZ. He only does Quads and been in business 40-50 years. I'm very happy with his work.

Normmus said:

I just did this last week on my '77. You are correct, there is a ground wire and a power wire, which was recommended to connect to the wiper motor wire. And of course the electric choke itself which mounts to the manifold. Nothing needs to be changed vacuum wise. I had been having choke problems with the divorced choke thermostat even after replacing it with a new part. The electric conversion seems to be working much better.

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To mimic the OEM electric choke trucks, it is recommended to wire that through an oil pressure switch. This will only provide power to the choke to pull it off when the engine is running. If you just run it through the ignition power you can't sit for any amount of time with the key on and engine off or you will kill the battery and it will pull the choke off without the engine actually being warm. You can thread it directly in place into the NPT hole right above the oil filter in the drivers side of the block. Depending on the engine, you might have a 1/8" NPT or a 1/4" NPT hole there. PS126 is the 1/8" switch and PS144 is for 1/4". You basically run the power however you want, then run the ground to one terminal of the switch and run a wire from the other terminal to a good ground location.

KevinP said:

Thanks. I have a rebuild kit and I have considered going that route. I'll check out the company you mentioned. I may buy a reman unit just to get it moving again quickly, and then rebuild the one that that is currently installed as a backup if I can determine that it is a real period-correct Q-jet. I like things to be as close to original as possible. I'm just not an aftermarket / performance guy. I feel like you change one thing and then you end up having to mess with everything.

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the divorced choke is a good sign it's the 'right time frame' quadrajet.

my '85 uses an electric 'all on the carb' choke.

i agree that not firing on ether or dribbled gas down the throat points at an ignition problem.
maybe in addition to a fuel delivery issue.

(my truck came with a clothespin holding the primary open)

good luck
'monkey

No doubt the previous owner was a member of the “Q-Jets are junk” group. He clearly had no idea how a Q-Jet works, especially on the secondary side.

Cliffs Q-Jet can help you with the parts you need.

A year ago, I had never touched a QJ. And I had friends saying, "just put a holley on it." (Bad advise)
I bought a couple books on QJ's. One was Cliff's. So over winter, I read the books, bought a couple QJ's off CL and bought rebuild kits. And over the winter, I rebuilt 2 of them for spares.
It was the best decision I could of made. I love QJ's and they are so freaking simple to work on, and tune, but you have to know what you are doing.
Cliff's is still in business and located about an hour north of Columbus, Ohio.
I think (not positive) he will even rebuild yours if you ship it to him.
So, a couple things...
My carb bolts were loose on mine, because the PO just tightened bolts instead of replacing the gasket under the carb. He just crushed it and 45 years later, it just broke down and leaked.
Any air /vacuum leaks will screw up the fuel/air circuits in the QJ and no amount of "screwdriver'n" will fix it.
Second, once you learn how to work on a QJ, the type of float matters not. Fiber or brass, will work just fine.
I have no issues with my brass float.
When you order kits, the 8 digit carb number is important. Having it handy is a smart move.

You can check out my QJ posts on here.
Don't let it intimidate you.
If you take the time to learn it, it will greatly reward you.

Bingo!! Exactly my point, the people who say Q-Jets are junk are either too lazy to study them, too stubborn to learn, or too stupid to understand them.

GM sold millions of vehicles with Q-Jets, every one of them was expected to start and run with drama or fuss, regardless of the environment. Properly calibrated and maintained, there is zero reason the won’t today.

Matt69olds said:

Bingo!! Exactly my point, the people who say Q-Jets are junk are either too lazy to study them, too stubborn to learn, or too stupid to understand them.

GM sold millions of vehicles with Q-Jets, every one of them was expected to start and run with drama or fuss, regardless of the environment. Properly calibrated and maintained, there is zero reason the won’t today.

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GM also spent hundreds of hours fine tuning them by application using tools that nearly no one else had access to at the time. And folks throw them away for a generic build holley or AFB and never even try to tune them. Its bananas.

Matt69olds said:

Bingo!! Exactly my point, the people who say Q-Jets are junk are either too lazy to study them, too stubborn to learn, or too stupid to understand them.

GM sold millions of vehicles with Q-Jets, every one of them was expected to start and run with drama or fuss, regardless of the environment. Properly calibrated and maintained, there is zero reason the won’t today.

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Correct, with one exception what is going in the gas tank.

77Dmax said:

GM also spent hundreds of hours fine tuning them by application using tools that nearly no one else had access to at the time. And folks throw them away for a generic build holley or AFB and never even try to tune them. Its bananas.

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Yep, other than idle speed and mixture, that’s as far as most people will go with tuning. Most people don’t have any jets, no float bowl gaskets, squirters, or pump cams.

Most of the same people who think their Holley carb is tuned have no clue what I just said means.

fast 99 said:

Correct, with one exception what is going in the gas tank.

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True, unfortunately today’s gas is much different than what came out of the pumps when these cars were new. Meaning some calibration changes are needed to compensate.

Matt69olds said:

Yep, other than idle speed and mixture, that’s as far as most people will go with tuning. Most people don’t have any jets, no float bowl gaskets, squirters, or pump cams.

Most of the same people who think their Holley carb is tuned have no clue what I just said means.

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Yep, most folks think as long as a carbed car starts and runs its good enough. I've seen plenty of very high dollar cars that have brand new carbs that barely function.

And some don't realize that not everybody's engine is a stock 305/350/454 that these trucks came with so factory tuning or what GM used doesn't apply or matter in the end

Application, application, application

Matt69olds said:

Yep, other than idle speed and mixture, that’s as far as most people will go with tuning. Most people don’t have any jets, no float bowl gaskets, squirters, or pump cams.

Most of the same people who think their Holley carb is tuned have no clue what I just said means.

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From what I have seen Q jets don't have that many different jets sizes. Lots of metering rod changes. I saved metering rods and jets out of nearly every carb I scrapped. Mostly because water sat inside.