What is this goofy thing? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jcfoote60 · 08-10-2005, 07:55 AM

I was working on my 72 Blazer some last night and kept looking at the strange stand tube thing that sits by the fuel filler in the bed. I decided rather than glancing at it and wondering what it did like I have done so many times before, I followed the lines back to the gas tank. What is this thing part of the emissions?? My 71 Jimmy has the same thing, do the 69 and 70's have this also? I am just curious more than anything about what it does...."officially".

KC

71swb4x4 · 08-10-2005, 08:25 AM

I am pretty sure you are talking about the vent tube.

jakeslim · 08-10-2005, 08:43 AM

my 69 has it

bouncytruck · 08-10-2005, 12:04 PM

Vent tube - so the gas can go in and the air can go out.

71RestoRod · 08-10-2005, 02:26 PM

Vapor tube.

It's an emissions thing but not at the cost of any HP and actually a good thing to have hooked up.

Lines from both sides of the gas tank attach to the bottom of it. A third line is attached and runs up into the tube to extract vapor only, not raw fuel. The vapor line is attached to a vapor canister mounted on the right front fender. The canister has two more hoses... one that tees into the PCV hose to the carb, and another vacuum line that goes to ported vacuum on the carb. When you have throttle above idle, the fumes from the gas tank get sucked into the PCV system and get burned along with the crankcase fumes.

The gas cap on this system is not vented. It allows air to enter the tank but not to exit.

jcfoote60 · 08-10-2005, 05:56 PM

Wow, great explanation! I appreciate it......actually provides a useful function so although it's odd looking piece of engineering it works!

08-10-2005, 07:55 AM	#1
jcfoote60 Active Member Join Date: Jun 2005 Location: Idaho Posts: 263	What is this goofy thing? I was working on my 72 Blazer some last night and kept looking at the strange stand tube thing that sits by the fuel filler in the bed. I decided rather than glancing at it and wondering what it did like I have done so many times before, I followed the lines back to the gas tank. What is this thing part of the emissions?? My 71 Jimmy has the same thing, do the 69 and 70's have this also? I am just curious more than anything about what it does...."officially". KC

08-10-2005, 08:25 AM	#2
71swb4x4 Senior Member Join Date: Nov 2003 Location: Brookings, SD Posts: 10,497	I am pretty sure you are talking about the vent tube. __________________ Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs.

08-10-2005, 08:43 AM	#3
jakeslim Premium Level Member Join Date: Aug 2004 Location: Northern CA Posts: 829	my 69 has it __________________ 69 K5 CST stock- 350, 4speed 77 K5 - 383, auto, 6" lift, D60 front, 14b rear, 39" tsl's,

08-10-2005, 12:04 PM	#4
bouncytruck SKINNY TIRES RULE! Join Date: Sep 2001 Location: Bothell, WA Posts: 11,038	Vent tube - so the gas can go in and the air can go out. __________________ bouncytruck 1972 K5 The Hauler 1994 K1500 Suburban The Daily2010 Kia Soul Wife's Ride2014 Fiat 500L

08-10-2005, 02:26 PM	#5
71RestoRod Registered User Join Date: Sep 2003 Location: Evergreen, CO Posts: 492	Vapor tube. It's an emissions thing but not at the cost of any HP and actually a good thing to have hooked up. Lines from both sides of the gas tank attach to the bottom of it. A third line is attached and runs up into the tube to extract vapor only, not raw fuel. The vapor line is attached to a vapor canister mounted on the right front fender. The canister has two more hoses... one that tees into the PCV hose to the carb, and another vacuum line that goes to ported vacuum on the carb. When you have throttle above idle, the fumes from the gas tank get sucked into the PCV system and get burned along with the crankcase fumes. The gas cap on this system is not vented. It allows air to enter the tank but not to exit. __________________ 71 Blazer / GMPP ZZ383 / MPFI / 700R4 / 4-Wheel Disk / Ground-up frame off almost completed resto-mod

08-10-2005, 05:56 PM	#6
jcfoote60 Active Member Join Date: Jun 2005 Location: Idaho Posts: 263	Wow, great explanation! I appreciate it......actually provides a useful function so although it's odd looking piece of engineering it works!



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