Fuel pump question? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Chevy Punk · 06-13-2003, 06:32 PM

Hey guys, I was wondering if you could help me with something. I bought a new fuel pump for the '75 350 that I put in my truck and it has three fittings on it. One is the inlet from the gas tank and one is the outlet to the carb. There is one other one that is in between the two and looks like the inlet but is about half the diameter of it. What is this for? as far as i can see there is nothing down there to hook it up to. Maybe I have the wrong fuel pump? BTW it is in my 71 Chevy that had a 350 in it. Thanks for the help.

ddsmith · 06-13-2003, 07:18 PM

I'm pretty sure that is a fuel return line to the tank. I think they installed fuel return lines to the tank to prevent vapor lock problems on some vehicles. As long as the gas was flowing somewhere like back to the tank it wouldn't heat up as much preventing so many vapor lock problems. I would check with the auto part store. The pump probably belongs on some other vehicle or the pump manufacture decided that the pump is the same as yours without addressing the port you speak of.

71GMC_3/4T · 06-13-2003, 07:27 PM

Go buy one for your year of truck, not the year of the engine. That's for the overflow/return in newer trucks with the smog control stuff.

cojnit · 06-13-2003, 07:50 PM

that sounds like the one for the '76 3/4 that I had. I think the 76 year was the year they changes all of the smog junk

Longhorn Man · 06-13-2003, 08:49 PM

And if you are unable to return it, a short hose with a bolt clamped in it with some RTV (fuel safe of corse) will solve any problems with it.
I agree with returning it and getting one for the 71 truck regardless of the engine year.

Chevy Punk · 06-13-2003, 10:28 PM

Thanks for the replies. Will there be any problems with plugging the return line? Does it have any pressure or vacuum from it that could cause the fuel pump or plug to fail? If not I think I will do that.

Project1970 · 06-14-2003, 11:07 AM

I've actually heard that plugging return lines on some pumps like that causes the fuel pressure to go too high for a carb...

Longhorn Man · 06-15-2003, 12:33 AM

Really?
I retract my statement, after thinking about it that does make plenty of sence.

06-13-2003, 06:32 PM	#1
Chevy Punk Registered User Join Date: Apr 2002 Location: Blaine WA Posts: 455	Fuel pump question? Hey guys, I was wondering if you could help me with something. I bought a new fuel pump for the '75 350 that I put in my truck and it has three fittings on it. One is the inlet from the gas tank and one is the outlet to the carb. There is one other one that is in between the two and looks like the inlet but is about half the diameter of it. What is this for? as far as i can see there is nothing down there to hook it up to. Maybe I have the wrong fuel pump? BTW it is in my 71 Chevy that had a 350 in it. Thanks for the help.

06-13-2003, 07:18 PM	#2
ddsmith Glowing since 1978 Join Date: Mar 2001 Location: Lusby,MD,USA Posts: 532	I'm pretty sure that is a fuel return line to the tank. I think they installed fuel return lines to the tank to prevent vapor lock problems on some vehicles. As long as the gas was flowing somewhere like back to the tank it wouldn't heat up as much preventing so many vapor lock problems. I would check with the auto part store. The pump probably belongs on some other vehicle or the pump manufacture decided that the pump is the same as yours without addressing the port you speak of. __________________ 66 Chevy C30 Stakebody Dump, PS,PB, 327cu in 71 Corvette Coupe 454 4 speed 69 Chevy C20 Custom Camper

06-13-2003, 07:27 PM	#3
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	Go buy one for your year of truck, not the year of the engine. That's for the overflow/return in newer trucks with the smog control stuff. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

06-14-2003, 11:07 AM	#7
Project1970 14.1 @ 96MPH Join Date: Jul 2001 Location: Mesa, AZ Posts: 2,811	I've actually heard that plugging return lines on some pumps like that causes the fuel pressure to go too high for a carb... __________________ Project1970 - LS1 Swap Complete!

06-13-2003, 07:50 PM	#4
cojnit Nothing clever Join Date: Jun 2003 Location: Kailua HI Posts: 828	that sounds like the one for the '76 3/4 that I had. I think the 76 year was the year they changes all of the smog junk

06-13-2003, 08:49 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	And if you are unable to return it, a short hose with a bolt clamped in it with some RTV (fuel safe of corse) will solve any problems with it. I agree with returning it and getting one for the 71 truck regardless of the engine year.

06-13-2003, 10:28 PM	#6
Chevy Punk Registered User Join Date: Apr 2002 Location: Blaine WA Posts: 455	Thanks for the replies. Will there be any problems with plugging the return line? Does it have any pressure or vacuum from it that could cause the fuel pump or plug to fail? If not I think I will do that.

06-15-2003, 12:33 AM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Really? I retract my statement, after thinking about it that does make plenty of sence.



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