72 Big Block Carb ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**uncle** · 04-08-2013, 05:02 PM

Have a 72 1/2 ton 402 w/ 7042218 carb and never had one with this xtra port on pass side of body. Took a few xtra pics. Can someone tell me how the vac lines route?
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**uncle** · 04-08-2013, 05:04 PM

Pic 2
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**uncle** · 04-08-2013, 05:06 PM

Pic 3
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**JQ-72** · 04-08-2013, 09:13 PM

Hey Tim, The extra port shown in your pictures is for the smog set up. Is your truck a 1/2 ton? I recently learned that all '72 1/2 tons came with somg. That's why I drove nearly 5 hours to your place to get that TLM suffix code motor!
Joshua

**Steeveedee** · 04-08-2013, 10:40 PM

I have a '70 Federal (which is different from California and High Altitude) Rochester QJ on a BB 400. It does not have this fitting. Perhaps it is for the vapor canister, which by 1972, iirc, was on all vehicles.

The fact that it is above the throttle plate tells me it is ported vacuum, so it isn't a vacuum leak at idle.

By the way, if you are experiencing surging at heavy loads or high speed, I'd blame that twisted fuel line where it goes into the carburetor. That's got to be a serious restriction in fuel flow.

**uncle** · 04-09-2013, 08:04 AM

Haven't driven it carb needs rebuild. Just trying to figure out vacuum line routing. It is a 1/2 ton. Thx. Josh have you delivered my blue truck to the Valley yet?

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**JQ-72** · 04-09-2013, 08:11 AM

I'll get a picture of mine later this week. I'm working 12 hour shifts now. Um, what blue truck to what valley? Are you referring to the possible trade with Jamie?
JQ

geezer#99 · 04-09-2013, 09:41 AM

[QUOTE

The fact that it is above the throttle plate tells me it is ported vacuum, so it isn't a vacuum leak at idle.

[/QUOTE]

Not necessarilly so. That vacuum port directly below it is manifold vacuum to the choke pull off pot.

**Dave** · 04-09-2013, 11:20 AM

From the number you posted on the carb, you have a 72 bb carb with auto. As far as the vacuum line routing, I'll get with you later its a little tricky. Gm was trying to delay the vacuum advance signal to the distributor and such.
Dave.
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**uncle** · 04-09-2013, 01:10 PM

Yea Josh I was just messin wit ya. Pics would be great when you get time
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**JQ-72** · 04-09-2013, 01:20 PM

OK, gotcha! I actually talked to Jamie last night and we are real close to making the deal.
JQ

Quote:

Originally Posted by uncle

Yea Josh I was just messin wit ya. Pics would be great when you get time
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04-08-2013, 05:02 PM	#1
uncle Senior Member Join Date: Aug 2003 Location: Conyers,Ga. Posts: 7,286	72 Big Block Carb ? Have a 72 1/2 ton 402 w/ 7042218 carb and never had one with this xtra port on pass side of body. Took a few xtra pics. Can someone tell me how the vac lines route? Posted via Mobile Device Attached Images

04-08-2013, 05:04 PM	#2
uncle Senior Member Join Date: Aug 2003 Location: Conyers,Ga. Posts: 7,286	Re: 72 Big Block Carb ? Pic 2 Posted via Mobile Device Attached Images

04-08-2013, 05:06 PM	#3
uncle Senior Member Join Date: Aug 2003 Location: Conyers,Ga. Posts: 7,286	Re: 72 Big Block Carb ? Pic 3 Posted via Mobile Device Attached Images

04-08-2013, 09:13 PM	#4
JQ-72 Senior Member Join Date: Feb 2001 Location: Killen, Alabama USA Posts: 3,574	Re: 72 Big Block Carb ? Hey Tim, The extra port shown in your pictures is for the smog set up. Is your truck a 1/2 ton? I recently learned that all '72 1/2 tons came with somg. That's why I drove nearly 5 hours to your place to get that TLM suffix code motor! Joshua __________________ 72 Cheyenne Super swb. Factory 402/400,tach,posi,AM/FM, A/C. Adding cruise, 8-track 72 Cheyenne Super swb. 350/350 A/C, bucket seats 72 Cheyenne swb. Factory 402/400, tilt, posi, A/C 72 Cheyenne Super K-10. 350/4 spd., posi. 72 Suburban 350/350 tilt, tach, AM/FM, A/C, luggage rack 72 GMC Sierra lwb. 350/350, A/C. medium green/olive interior

04-08-2013, 10:40 PM	#5
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,329	Re: 72 Big Block Carb ? I have a '70 Federal (which is different from California and High Altitude) Rochester QJ on a BB 400. It does not have this fitting. Perhaps it is for the vapor canister, which by 1972, iirc, was on all vehicles. The fact that it is above the throttle plate tells me it is ported vacuum, so it isn't a vacuum leak at idle. By the way, if you are experiencing surging at heavy loads or high speed, I'd blame that twisted fuel line where it goes into the carburetor. That's got to be a serious restriction in fuel flow. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

04-09-2013, 08:04 AM	#6
uncle Senior Member Join Date: Aug 2003 Location: Conyers,Ga. Posts: 7,286	Re: 72 Big Block Carb ? Haven't driven it carb needs rebuild. Just trying to figure out vacuum line routing. It is a 1/2 ton. Thx. Josh have you delivered my blue truck to the Valley yet? Posted via Mobile Device

04-09-2013, 08:11 AM	#7
JQ-72 Senior Member Join Date: Feb 2001 Location: Killen, Alabama USA Posts: 3,574	Re: 72 Big Block Carb ? I'll get a picture of mine later this week. I'm working 12 hour shifts now. Um, what blue truck to what valley? Are you referring to the possible trade with Jamie? JQ __________________ 72 Cheyenne Super swb. Factory 402/400,tach,posi,AM/FM, A/C. Adding cruise, 8-track 72 Cheyenne Super swb. 350/350 A/C, bucket seats 72 Cheyenne swb. Factory 402/400, tilt, posi, A/C 72 Cheyenne Super K-10. 350/4 spd., posi. 72 Suburban 350/350 tilt, tach, AM/FM, A/C, luggage rack 72 GMC Sierra lwb. 350/350, A/C. medium green/olive interior

04-09-2013, 09:41 AM	#8
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,546	Re: 72 Big Block Carb ? [QUOTE The fact that it is above the throttle plate tells me it is ported vacuum, so it isn't a vacuum leak at idle. [/QUOTE] Not necessarilly so. That vacuum port directly below it is manifold vacuum to the choke pull off pot.

04-09-2013, 11:20 AM	#9
Dave DND Trucks Join Date: Dec 1999 Location: NW Indiana Posts: 2,380	Re: 72 Big Block Carb ? From the number you posted on the carb, you have a 72 bb carb with auto. As far as the vacuum line routing, I'll get with you later its a little tricky. Gm was trying to delay the vacuum advance signal to the distributor and such. Dave. Posted via Mobile Device

04-09-2013, 01:10 PM	#10
uncle Senior Member Join Date: Aug 2003 Location: Conyers,Ga. Posts: 7,286	Re: 72 Big Block Carb ? Yea Josh I was just messin wit ya. Pics would be great when you get time Posted via Mobile Device



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