72 C-20 Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

saddletramp · 04-05-2021, 03:21 PM

Sorry forgot my picture what am i missing on my Q-jet carb im not hearing the back 2 barrel's opening up when i mash the gas any help and pictures appreciate you guys Saddletramp

**Wrenchbender Ret** · 04-05-2021, 04:10 PM

Your choke is partally closed. It must be fully open for the secondary throttle to open.
George

**Steeveedee** · 04-05-2021, 04:18 PM

Try pushing the choke plate all the way open (engine off!). Then open the throttle and watch the linkage on the driver's side to see if the secondary shaft rotates. If not, it's possible that the choke link isn't releasing all the way. Also make sure that the fast idle cam drops all the way down when you are holding the choke open. That's the lever right next to the body of the carburetor, inside where the vacuum pull-off linkages are. Also, make sure that the choke pull-off works. The top linkage prevents the secondary air valve from opening with the choke closed. That is the top link that is attached to the choke pull-off.

**Rich72C10** · 04-05-2021, 04:26 PM

The left side of the photo is cutting what I am looking at but it looks like the vacuum coming off the passenger side of the cab is going into a "T" that is also connected to the manifold vacuum? That can't be right?

my understanding (which could be wrong) that goes to the charcoal canister that is next to the battery (assuming you have have 3 port fuel pump and EEC Tank).

**Steeveedee** · 04-05-2021, 05:52 PM

Quote:

Originally Posted by Rich72C10

The left side of the photo is cutting what I am looking at but it looks like the vacuum coming off the passenger side of the cab is going into a "T" that is also connected to the manifold vacuum? That can't be right?

my understanding (which could be wrong) that goes to the charcoal canister that is next to the battery (assuming you have have 3 port fuel pump and EEC Tank).

Yeah, I wasn't going to address that, just yet. It may be that the line just runs back that way because the air cleaner is laid back out of the picture?

mr.mud1 · 04-05-2021, 06:24 PM

yes sir,all good info,the secondaries won't open unless the choke if off,and you don't need the nut on the air cleaner stud way down at the top of the air horn.the wingnut on top holds it all together.the nut might get in the way of the secondary metering rod hanger lifting up and allowing fuel to flow to the secondaries.

**BigBird05** · 04-05-2021, 07:10 PM

Your picture is not showing the left side of the carb. Have a helper press down on the gas pedal and take a picture to see if your throttle linkage is opening all the way.

04-05-2021, 03:21 PM	#1
saddletramp Registered User Join Date: Aug 2014 Location: murfreesboro tn Posts: 283	72 C-20 Help Sorry forgot my picture what am i missing on my Q-jet carb im not hearing the back 2 barrel's opening up when i mash the gas any help and pictures appreciate you guys Saddletramp Attached Images Last edited by LockDoc; 04-05-2021 at 04:15 PM. Reason: Rotated picture

04-05-2021, 04:10 PM	#2
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,190	Re: 72 C-20 Help Your choke is partally closed. It must be fully open for the secondary throttle to open. George

04-05-2021, 04:18 PM	#3
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,088	Re: 72 C-20 Help Try pushing the choke plate all the way open (engine off!). Then open the throttle and watch the linkage on the driver's side to see if the secondary shaft rotates. If not, it's possible that the choke link isn't releasing all the way. Also make sure that the fast idle cam drops all the way down when you are holding the choke open. That's the lever right next to the body of the carburetor, inside where the vacuum pull-off linkages are. Also, make sure that the choke pull-off works. The top linkage prevents the secondary air valve from opening with the choke closed. That is the top link that is attached to the choke pull-off. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA Last edited by Steeveedee; 04-05-2021 at 04:23 PM.

04-05-2021, 04:26 PM	#4
Rich72C10 Mr. Cheyenne Join Date: Jun 2020 Location: Kyle, Texas Posts: 1,643	Re: 72 C-20 Help The left side of the photo is cutting what I am looking at but it looks like the vacuum coming off the passenger side of the cab is going into a "T" that is also connected to the manifold vacuum? That can't be right? my understanding (which could be wrong) that goes to the charcoal canister that is next to the battery (assuming you have have 3 port fuel pump and EEC Tank). __________________ Richard *'72 Chevy C10 Cheyenne Super WHT/MED BRONZE/WHT SBC 350 \| TH350 \| LWB \| AC \| Buddy Seats Upgrades:** Tilt \| Front Sway Bar \| Radio \| Sliding Window \| Bed Spare w/Lock Bed Rails \| Full LEDs \| Courtesy Lights \| Tachometer \| Glovebox Lock & Light \| Head Light Relays \| *Upgraded Fully Super Trim

04-05-2021, 06:24 PM	#6
mr.mud1 Registered User Join Date: Dec 2020 Location: Joggins Nova Scotia Posts: 1,599	Re: 72 C-20 Help yes sir,all good info,the secondaries won't open unless the choke if off,and you don't need the nut on the air cleaner stud way down at the top of the air horn.the wingnut on top holds it all together.the nut might get in the way of the secondary metering rod hanger lifting up and allowing fuel to flow to the secondaries.

04-05-2021, 07:10 PM	#7
BigBird05 Senior Member Join Date: Aug 2019 Location: Cheraw Posts: 1,305	Re: 72 C-20 Help Your picture is not showing the left side of the carb. Have a helper press down on the gas pedal and take a picture to see if your throttle linkage is opening all the way.



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