Secondary Choke Pull Off—Needed?
- Thread starter DWCaprice2017
- Start date
Generally speaking, Chevies didn't use them like Olds did. Are they necessary? IMO, ONLY if you live in Canada or places where it gets super cold. It's really only there to pull the choke open just a bit more when it's 9000 degrees below zero , and although I could find no documentation for it, I believe it's mostly used on hot air chokes. They take a bit more time than electric chokes to get up to speed. If it doesn't consistently get below 0 degrees where you drive, I wouldn't worry too much about it.
Thanks for the quick response!
In my searching for all of the vacuum ports on the carb and intake manifold, I saw the empty screw holes and started to wonder if some unknowing DIYer took it off. The car originally went to a family in Central California, so low temperature days were seldom.
Chevy versions of the CCC Qjet did not use rear choke pulloffs. Likely because they won't clear the EGR valve. Every division had their own carb and CCC setup.
I took a look at one I have, and what you have is how it should look. If you notice, on the primary choke pull off you have the linkage rod that comes across and hooks to the secondary butterflies. This is the way it should be.
Under vacuum the primary pull off opens the choke plate after the car starts. This allows metered air into the primary bores and allows the engine to run at idle, starting at idle and continuing until the choke is completely open.
Once the choke is completely open it no longer needs the assistance of the pull off as far as the primary bores are concerned. However under vacuum this is still keeping the secondary butterflies shut. You do not want the secondary butterflies to open until you are accelerating and/or going toward wide open throttle.
On the quadrajet, as the secondary throttle plates open, this applies vacuum into the secondary bores and the top butterflies. As the butterflies start to move down and allowing air into the secondary bores, this will cause the secondary rods to move up. When the secondary rods move up, this allows fuel to enter the secondary bores. If the secondary butterflies are allowed to open while you're at idle or low Cruise you will start flooding and loading up the engine and obviously you don't want that.
So the way you have yours is the way it should be. There is no secondary pull-off the way yours is designed.
Under vacuum the primary pull off opens the choke plate after the car starts. This allows metered air into the primary bores and allows the engine to run at idle, starting at idle and continuing until the choke is completely open.
Once the choke is completely open it no longer needs the assistance of the pull off as far as the primary bores are concerned. However under vacuum this is still keeping the secondary butterflies shut. You do not want the secondary butterflies to open until you are accelerating and/or going toward wide open throttle.
On the quadrajet, as the secondary throttle plates open, this applies vacuum into the secondary bores and the top butterflies. As the butterflies start to move down and allowing air into the secondary bores, this will cause the secondary rods to move up. When the secondary rods move up, this allows fuel to enter the secondary bores. If the secondary butterflies are allowed to open while you're at idle or low Cruise you will start flooding and loading up the engine and obviously you don't want that.
So the way you have yours is the way it should be. There is no secondary pull-off the way yours is designed.
I'm in northwest Ohio. Now while I can't remember about the original carb on my El Camino if it had it or not, but I THINK it did, I've had about a dozen other 305-454 chevy engines around with the quadrajet, and they have all had the pull off. Now none of them were the ccc carbs, but some had electric choke, and some were hot air.
Let me preface this that the parts book doesn't show the 17084201 B and G body 305 H engines as having a secondary pull off. So I would base off that the your carb did not come with a secondary pull off.
I know it's not entirely applicable to the original post, but I did find out some more stuff about Chevy carbs and secondary pull offs. Apparently SOME Chevies come with secondary pulloffs according to the 86 CSM adjustment specs on some 350 and 262 applications (see chart below). Appears it's trucks and vans though with 1985/86 year designations, based on the applications of the carb. Not sure what those are doing in this chart, unless it's just a comprehensive chart they jam in all the Chevy CSMs. From my experience, Olds just listed applicable carb numbers. I got a GM tuneup book for GM cars of the era listing all these specs, just forgot where I put it atm.
Here's a pic of a 17085502. I guess that blows up the electric chokes not having secondary pull offs theory. It appears too, the location of the pull off wouldn't interfere with the EGR valve as far as clearances.
And a 17085508
And one more, a 17085524. All appear to have electric chokes. Makes sense since Chevy intakes are super narrow. But I believe earlier Q-jets had hot air chokes, but not the CCC versions. I don't think. No expert on that.
I know it's not entirely applicable to the original post, but I did find out some more stuff about Chevy carbs and secondary pull offs. Apparently SOME Chevies come with secondary pulloffs according to the 86 CSM adjustment specs on some 350 and 262 applications (see chart below). Appears it's trucks and vans though with 1985/86 year designations, based on the applications of the carb. Not sure what those are doing in this chart, unless it's just a comprehensive chart they jam in all the Chevy CSMs. From my experience, Olds just listed applicable carb numbers. I got a GM tuneup book for GM cars of the era listing all these specs, just forgot where I put it atm.
Here's a pic of a 17085502. I guess that blows up the electric chokes not having secondary pull offs theory. It appears too, the location of the pull off wouldn't interfere with the EGR valve as far as clearances.
And a 17085508
And one more, a 17085524. All appear to have electric chokes. Makes sense since Chevy intakes are super narrow. But I believe earlier Q-jets had hot air chokes, but not the CCC versions. I don't think. No expert on that.
I should add myself, that the engines I had, mostly came from either 70's or 80's big cars, or pickups, not 80's that had the ccc carbs.
In the 80s only Chevy US cars had full CCC systems. 80s Chevy trucks did not receive full CCC systems. pretty much just ESC and a weird two mode accel pump called Dual Capacity Accerator Pump (DCP). The Chevy truck Qjets lack M/C solenoids and TPS, instead they had a semi computer controlled Dual Capacity Accerator Pump with a grey connector instead of a blue connector for M/C solenoids. Trucks have less stringent emissions and gas mileage govt mandated requirements than cars, which is why most manufacturers mostly make truck based vehicles today.
Truck DCP Qjet.
Full CCC Car Qjet
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