Quadrajet Rear Choke Pull Off Question

[1970GMC350]

I’m in the process of relocating/replacing some vacuum lines. The rear choke pull off on my Quadrajet has two lines coming out of it - one small vacuum line hooked up to a vacuum port in the back base of my carburetor and a bigger line that runs into the PCV valve on the driver’s side valve cover. I’m wanting to run a line from that PCV to the bigger port on the front of the carb but am not sure what to do with the bigger line coming off of the back of the choke pull off. I can’t find any information on this and I’m at a loss. What should I do with that other line? Does that also need a vacuum source or is it some type of breather? Thank you in advance for any help. This is the best photo I currently have but I can’t find any take some better photos when I get home if needed.

[RustyPile]

This question begs to be asked.. Why do you feel the need to "redesign" vacuum hose routing?? That choke pull performs more than one function.. Disrupting those functions could introduce problems that didn't exist prior to the changes. In other words -- "If it ain't broke, don't fix it"...

[1970GMC350]

Originally Posted by RustyPile

This question begs to be asked.. Why do you feel the need to "redesign" vacuum hose routing?? That choke pull performs more than one function.. Disrupting those functions could introduce problems that didn't exist prior to the changes. In other words -- "If it ain't broke, don't fix it"...

It all started with a post, I think on here, that I came across stating the “factory correct” way to route that PCV line was to the port on the front of the carb and it snowballed from there lol

I also ran a line to my air cleaner to operate the flap in it, kind of going for a more factory correct look overall. I just couldn’t figure out why that rear choke pull off needed two vacuum lines and am stumped.

[RustyPile]

Originally Posted by 1970GMC350

It all started with a post, I think on here, that I came across stating the “factory correct” way to route that PCV line was to the port on the front of the carb and it snowballed from there lol

I also ran a line to my air cleaner to operate the flap in it, kind of going for a more factory correct look overall. I just couldn’t figure out why that rear choke pull off needed two vacuum lines and am stumped.

Just because you saw it on the internet doesn't mean it's correct and accurate information. I've been doing this stuff for many years, 35 of those years as a GM mechanic.. Although vacuum hose routing changed from year to year, I can't remember seeing a choke pull that had 2 vacuum fittings. A picture showing that setup might be of some help.. Also, the Factory Service Manual for the year of your vehicle would be a good reference that shows the "factory correct" hose routing.

[1970GMC350]

Originally Posted by RustyPile

Just because you saw it on the internet doesn't mean it's correct and accurate information. I've been doing this stuff for many years, 35 of those years as a GM mechanic.. Although vacuum hose routing changed from year to year, I can't remember seeing a choke pull that had 2 vacuum fittings. A picture showing that setup might be of some help.. Also, the Factory Service Manual for the year of your vehicle would be a good reference that shows the "factory correct" hose routing.

Agreed, I should be more skeptical with information on the internet. I attached two pictures and circled the lines in green. The one bigger line attaches on the backside and the vacuum line attached to the back side of the carburetor comes off of the side of the choke pull off. I really appreciate any help.

[RustyPile]

I've never seen the hose for a pcv valve get it's vacuum source from a choke pull, never.. What I have seen is some aftermarket vacuum pulls having a travel adjustment on the back side. I've not seen many of these, only a very few.. Are you sure that large "port" actually applies vacuum to the pcv hose?? Start the engine and check for vacuum at the pcv valve itself..

[1970GMC350]

Originally Posted by RustyPile

I've never seen the hose for a pcv valve get it's vacuum source from a choke pull, never.. What I have seen is some aftermarket vacuum pulls having a travel adjustment on the back side. I've not seen many of these, only a very few.. Are you sure that large "port" actually applies vacuum to the pcv hose?? Start the engine and check for vacuum at the pcv valve itself..

I will have to check vacuum on that when I’m off work. Could that port possibly be an air bleed/vent? If it is, and if it doesn’t provide any vacuum, should I just route my pcv to the big port on the front of the carb and leave that port on the choke pull off open? I’m starting to wonder if the shop that did my carb work got their lines mixed up.

[Steeveedee]

Looks like a stock carb converted to integral electric choke. I see holes where the choke pull off would go if it were the standard (factory) divorced choke. Or am I missing something? And for sure that PCV hose should be connected to the port on the front, with nothing else tapped into it. The carburetor is calibrated for that flow.

ETA: The integral choke uses a piston inside the housing for choke pull off, right? if it is an aftermarket piece, maybe not. But that choke uses the port that goes to the air cleaner heat flap. What is the number on the carb?

[1970GMC350]

Originally Posted by Steeveedee

Looks like a stock carb converted to integral electric choke. I see holes where the choke pull off would go if it were the standard (factory) divorced choke. Or am I missing something? And for sure that PCV hose should be connected to the port on the front, with nothing else tapped into it. The carburetor is calibrated for that flow.

ETA: The integral choke uses a piston inside the housing for choke pull off, right? if it is an aftermarket piece, maybe not. But that choke uses the port that goes to the air cleaner heat flap. What is the number on the carb?

17084226 is the carb number. I was having carb issues in the past and had to take it to a shop to get it figured out. They swapped my old one with this one as they recommended the electric choke. I can run the pcv line to the front of the carb.

[pontiacvince]

What year is the truck and/or engine? I'm a Q-jet guy, but that doesn't look like a 60's or 70's style. All the earlier style Q-jets I've ever seen or worked on had the choke pull-off where the 2 holes are at the front of yours. And the electric choke looks to be an add-on.

[60case]

That is not a vacuum port. There is an adjustment screw in there it should have an allen head screw The small line is the vacuum supply to the choke pull off. The way it is hooked up it is just plugging the big line

[Steeveedee]

Originally Posted by 1970GMC350

17084226 is the carb number. I was having carb issues in the past and had to take it to a shop to get it figured out. They swapped my old one with this one as they recommended the electric choke. I can run the pcv line to the front of the carb.

OK, I see now. Can you get your original carb back from them? There are reliable rebuilders who can bring your carb back to pretty much original equipment levels of performance, and set it up and run it on an engine before sending it back. These guys at least used to do that, though Cliff himself has retired. Last kit I bought for my truck, I corresponded with Cliff directly.

https://cliffshighperformance.com

ETA- really try to get your original carb back. That looks like a later smog carburetor that can't possibly have the right calibration characteristics for your truck.

[Rust_never_sleeps]

FTR, there are ‘letric choke conversions for divorced chokes. They’re clunky to look at, but not sure I’d just swap a carp to get

Mike’s Carburetors has pretty good tehc doc’s and I like how he lays out information better than Cliff’s book.
I’ve gotten a few skull-imploding answers from Cliff’s q-jet forum, but there are mostly very knowledgable folks on there and Cliff himself still chimes in. Definitely an interesting enough variation to elicit some response

[Steeveedee]

I have an electric choke from Mike's, myself. Easy to install, and it works great. BUT, the OP's mechanic replaced the entire carb and did strange (to me) stuff on it...and it's not working properly for him. There are carb experts out there other than Cliff. I've had good luck with his parts and advice. I know other people who swear by different rebuilders. Everyday Performance is another rebuilder I've seen excellent results from, when it comes to carburetors, and he also does some great restoration plating.

[1970GMC350]

I really appreciate all of the help!

Originally Posted by pontiacvince

What year is the truck and/or engine? I'm a Q-jet guy, but that doesn't look like a 60's or 70's style. All the earlier style Q-jets I've ever seen or worked on had the choke pull-off where the 2 holes are at the front of yours. And the electric choke looks to be an add-on.

Both the truck and engine are 1970. I ran the carb number and I think it's an early 80's carb that's been remanufactured. The two holes being in the front makes me wonder if it's supposed to have the front choke pull-off.

Originally Posted by 60case

That is not a vacuum port. There is an adjustment screw in there it should have an allen head screw The small line is the vacuum supply to the choke pull off. The way it is hooked up it is just plugging the big line

Interesting. Could I just delete that line entirely?

Originally Posted by Steeveedee

OK, I see now. Can you get your original carb back from them? There are reliable rebuilders who can bring your carb back to pretty much original equipment levels of performance, and set it up and run it on an engine before sending it back. These guys at least used to do that, though Cliff himself has retired. Last kit I bought for my truck, I corresponded with Cliff directly.

https://cliffshighperformance.com

ETA- really try to get your original carb back. That looks like a later smog carburetor that can't possibly have the right calibration characteristics for your truck.

My original one is gone but I do have a spare Q-jet that I kept for spare parts. I believe it's all complete so sending that one in could definitely be an option. I had this work done a few years back and the shop said it was remanufactured and I never put too much thought in it as the truck runs and drives great.

Originally Posted by Rust_never_sleeps

FTR, there are ‘letric choke conversions for divorced chokes. They’re clunky to look at, but not sure I’d just swap a carp to get

Mike’s Carburetors has pretty good tehc doc’s and I like how he lays out information better than Cliff’s book.
I’ve gotten a few skull-imploding answers from Cliff’s q-jet forum, but there are mostly very knowledgable folks on there and Cliff himself still chimes in. Definitely an interesting enough variation to elicit some response

Yeah, I kind of regret listening to the shop and dumping my last carb all over a choke but I'll chalk it up as a valuable lesson. Truck runs and drives great, just got a little wild hair about my vacuum lines and went down a rabbit hole lol

I'll have to check them out.

Originally Posted by Steeveedee

I have an electric choke from Mike's, myself. Easy to install, and it works great. BUT, the OP's mechanic replaced the entire carb and did strange (to me) stuff on it...and it's not working properly for him. There are carb experts out there other than Cliff. I've had good luck with his parts and advice. I know other people who swear by different rebuilders. Everyday Performance is another rebuilder I've seen excellent results from, when it comes to carburetors, and he also does some great restoration plating.

I'll have to check them out as well.

[geezer#99]

Originally Posted by Steeveedee

Looks like a stock carb converted to integral electric choke. I see holes where the choke pull off would go if it were the standard (factory) divorced choke. Or am I missing something?

You are missing something.
Just because there’s a couple extra holes in the carb body doesn’t mean something is missing.
Here’s a carb with only a rear pull off.


https://www.amazon.ca/NENKUTEN-Carbu.../dp/B09BZ1VCBM

[Steeveedee]

Originally Posted by geezer#99

You are missing something.
Just because there’s a couple extra holes in the carb body doesn’t mean something is missing.
Here’s a carb with only a rear pull off.


https://www.amazon.ca/NENKUTEN-Carbu.../dp/B09BZ1VCBM

OK. Do you have a solution for his issue?

[67swb72klb]

Seen this the other day from the older Qjets...

[RustyPile]

For the purpose of this post, I'll use the term "vacuum powered device".. Some of those Q-Jets had the choke pull mounted on the front, and a second "vacuum powered device" on the rear. When equipped with 2 of these devices, the one on the rear functioned as a secondary air valve (the big "flapper valve" on top of the secondaries) inhibit.. These Q-Jets were equipped with a divorced choke. Until the choke control spring reached maximum temperature, a small "L" shaped bar was held in contact with the secondary throttle plates, prevented them from opening. The vacuum supply to that rear "vacuum powered device passed through a temperature sensor switch. When this switch opened, vacuum was applied to the rear "vacuum powered device". The arm retraced and "freed up" the secondary air valve..

In later years, The temperature switch was eliminated and the rear "vacuum powered device" performed dual duties -- Choke pull AND secondary air valve inhibit.. This one operated 2 rods.. The rod going to the choke lever had a "horseshoe bend" in it... Opening and/or closing this bend was/is how the amount of "pull" is applied to the choke lever.

[geezer#99]

Originally Posted by Steeveedee

OK. Do you have a solution for his issue?

Do better research.
Like this for vacuum diagrams.

https://www.google.ca/search?q=vacuu...dj&sclient=img

[1970GMC350]

I reached out to Cliff, as rust_never_sleeps recommended, and he confirmed that the shop screwed up running a line to that.

Originally Posted by geezer#99

Do better research.
Like this for vacuum diagrams.

https://www.google.ca/search?q=vacuu...dj&sclient=img

Believe me, I did a ton of research before asking here as nothing specifically addressed a rear choke pull off like mine. I was pretty confident on the vacuum line on the side but couldn’t find anything on the bigger port on the back or why my shop would’ve run a line to that.

[RustyPile]

Originally Posted by 1970GMC350

I will have to check vacuum on that when I’m off work. Could that port possibly be an air bleed/vent? If it is, and if it doesn’t provide any vacuum, should I just route my pcv to the big port on the front of the carb and leave that port on the choke pull off open? I’m starting to wonder if the shop that did my carb work got their lines mixed up.

No, it's not an "air bleed or vent".. In response to your last statement.. Run, don't walk, far from that shop.. It's obvious they know nothing about carburetors. Read post #11

[Rust_never_sleeps]

If it runs and drives well, they probably didn’t do anything stupid with jets/rods, which is common when people just slap on a q-jet from a rando donor vehicle, so nice to have avoided that cowpie

Also, carb they gave you does have APT, so maybe that’s an upgrade over what you had, but you probably need to strip it down and build back the way Mr Rochester intended

[Rust_never_sleeps]

As I often say, this guy’s work illustrates the difference between clever and smart

[geezer#99]

Originally Posted by Rust_never_sleeps

Also, carb they gave you does have APT, so maybe that’s an upgrade over what you had,

Did you know that all quadrajets have an APT.