choke pulloff linkage question and - 17080213

[sploke]

I tore this carb down to clean and rebuild it, and took a bunch of pictures in the process, so I'm about 95% sure I put this back together the way it was when I took it apart...but I'm also like 80% sure it's not attached correctly.  The rear choke pulloff has two attachment points on the plunger....I think the outermost one (closest to the camera in the first pic) should not be used, and the linkage rod that is attached to that one should actually go from the secondary air valve shaft to the front choke pulloff.  I.e. 180 degrees from how it is now.  Is that correct?

Also, the front choke pulloff fails the vacuum test so I need to replace that...is this the correct replacement?

https://cliffshighperformance.com/Quadrajet-rebuild-kits-and-quadrajet-parts/quadrajet-76-choke-pull-off









Also - what is this vacuum device?  It's hooked up to what I understand is the distributor vacuum advance port on the carb body, and it extends when I apply vacuum, but not far enough to interact with the throttle lever so I'm not sure about what it's purpose is.

[Kenth]

You have a 1979-80 Chevy/GMC Truck Quadrajet. Very nice units.
Your first three pictures shows the upper, air valve, link mounted in the wrong direction.
Your 4:th picture shows a front choke pull-off that does not belong to this style Truck Quadrajets. All the choke pull-off and air valve dampening is handled by the rear unit.
Your last two pictures shows a throttle lever actuator which is connected to the ignition spark port. This actuator has no real purpose on a properly modified/adjusted Truck Quadrajet.

Hope this helps some.

[sploke]

Very helpful, thanks.  So the outer linkage I need to flip around to the air valve link.  I think it also need some significant adjustment because when the pulloff actuates, it is not engaging the air flap at all.

Good news that the front pulloff isn't needed, so if it doesn't work I can just eliminated it entirely.

I'll also remove the throttle lever actuator if that's not needed either.

The carb is being mated to it's original 350, which came out of a 1984 truck, but it's being used to repower an old farm tractor.

[Cliff Ruggles]

The only thing I can add is that some of those carbs used a front pull-off, which is OK but isn't needed provided the rear one works and is adjusted correctly. 

The front pull-off simply becomes the "secondary" pull-off and the rear one is the "primary" in that scenario.......Cliff

[sploke]

Can it even be considered a secondary pulloff if there's no linkage attached to it?  There's an adjustment screw attached to it, but no linkage to engage with the air valve.

[Kenth]

Yes, flip the air valve link so the 90 degree bend will hang at the air valve. This link will hold the air valves closed in high vacuum as with low load on engine. At WOT it dampens the opening speed of the air valves and reduces fluctuations on the valves.

I have never seen a 1979 and later Truck Quadrajet using the rear dual purpose choke pull-off using also a front pull-off of any kind. Nowhere to hook it up.
1975 and later M-style Passenger Quadrajets on the other hand uses both front and rear pull-off

[Kenth]

For some unknown reason i am having a hard time to post on this site, only parts of my posting will show.

I will try again.

Yes, flip the air valve link so the 90 degree bend will hang at the air valve. This link will hold the air valves closed in high vacuum as with low load on engine. At WOT it dampens the opening speed of the air valves and reduces fluctuations on the valves.

I have never seen a 1979 and later Truck Quadrajet using the rear dual purpose choke pull-off using also a front pull-off of any kind. Nowhere to hook it up.
1975 and later M-style Passenger Quadrajets on the other hand uses both front and rear pull-offs, and always with the front as the primary unit. The rear secondary p-o on these carbs works for faster opening of the choke-blade at hot engine starts to hold down emissions. The secondary p-o is really not needed on a modified engine and with the front primary unit properly adjusted.

[tayto]

My 1986 non-CCC truck qjet only came with the front pull off, no rear pull off, also cliff only sent me a front pull off because mine didn't pass vac test.

Is that throttle lever actuator for anti-dieseling at shutdown? vs the electric ones for A/C idle?

[Cliff Ruggles]

Kenth, LOTS of later 1980's truck Q-jets used a front pull-off as the "secondary" pull-off.  The rear has two links, the front one engages with the choke linkage to unload the choke only and is adjustable via the spring loaded screw on it.......FWIW......Cliff

[Kenth]

My 1986 non-CCC truck qjet only came with the front pull off, no rear pull off, also cliff only sent me a front pull off because mine didn't pass vac test.

Is that throttle lever actuator for anti-dieseling at shutdown? vs the electric ones for A/C idle?

Some of the very latest made truck Qjets uses only the front/primary pull-off.
The throttle actuator on the truck units was aimed to reduce emissions by opening the throttle blades slightly at deceleration.

[Kenth]

Kenth, LOTS of later 1980's truck Q-jets used a front pull-off as the "secondary" pull-off.  The rear has two links, the front one engages with the choke linkage to unload the choke only and is adjustable via the spring loaded screw on it.......FWIW......Cliff

Cliff, thank you, i had to check my book and of course you are correct. Learn something every day!
And, the OPs carb 17080213 is one of these units using the dual action rear p-o and a front p-o also.
Seems a little overkill with the added front p-o but it was used from factory.

[Cliff Ruggles]

I typically don't install them and they would only be used if the rear or "primary" pull-off failed.

Same thing with the earlier carbs that used the front as the primary with the link up to the secondaries, installing the rear or "secondary" pull-off is not needed. 

I don't like those anyhow as many have a small bleed hole in them.....

[Pav8427]

Good morning gentlemen. For future reference, is there a easy way to tell on the carbs that come factory with 2 PO's, which one is being used as the primary?
Thanks. Doug

[tayto]

I think the rear one is "primary" if it has 2 rods. i rebuilt a 301 firebird carb 4 years ago for a friend and the rear pull off only had 1 rod. it didn't pass vac test and i got the ok from cliff to remove it. something about if the front pull off failed the rear would still eventually hold the choke open and prevent a no start and tow fee for the dealer while the car was still under warranty.

[Cliff Ruggles]

Just take a look at the secondary airdoor shaft.  If it has a slot for the link the front P/O is the "primary".

If it has a round hole for the link the rear P/O is the primary.

They can be converted to front P/O, I do it all the time.  You will need a front P/O, secondary shaft with a "slot" instead of a hole, and make or fabricate a stop for it.

Several easy ways to make a stop, the easiest is to install a divider in the main casting with the "hood" on one or both sides. 

If not I drill thru the casting and install a 4-40 allen head machine screw for the stop.  I've seen other ways but those are the easiest........Cliff