1978 fuel pump help!!
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Joined: Jan 2011
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1978 fuel pump help!!
I am replacing my fuel pump which has a 3rd line for a return line. Holley and all other aftermarket pumps only have 2. Do you experts see a problem simply plugging the return line?
Racer
Joined: Oct 2003
Posts: 424
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From: Killeen Texas
Did you already purchase a new pump w/ only the two hard lines coming out? I bought a replacement pump from NAPA about two or so years ago and it has three lines like the original one. The third line, the return, is a good thing, keeping the fuel cooler. I don't think it does as well as "Y-ing" it off just before the carb inlet and using an electric pump and regulator, but I personally wouldn't plug it off. I don't think it would hurt anything if you blocked it off, but the difference in price between the two and three line pump is nothing or next to it. Hope I answered your question. I'm now wondering what year GM started installing the pump w/ a return line, if it was sometime in '78 where some '78s had it and some didn't. I know that any place I checked f/ my '81 showed the three line pump. Maybe the computer in the auto parts places doesn't show that the '78 used a three line pump. Is your 'Vette a late '78?...like mfgd.late in the year? Just a guess. Check on what pump the '79 uses. In any event, let us know what the outcome is. Good Luck.
***In the '81 GM Shop Manual, it states: install the fuel return hose, if so equipped.
***In the '81 GM Shop Manual, it states: install the fuel return hose, if so equipped.
Last edited by texas jim; Feb 24, 2011 at 12:08 AM.
Le Mans Master
Joined: Sep 2002
Posts: 5,236
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From: Myrtle Beach SC
I suspect the aftermarket pumps are intended to bypass the vapor/fuel emission requirements just as dual exhaust systems bypass exhaust emission requirements such as a catalytic converter.
So if you put a high performance fuel pump on a low performance motor, I would suspect that you'll be pushing more fuel into the carb without the motor's ability to consume it or without the option to recycle unspent fuel. If you plug the return line, it will block fuel tank vapors and give the appearance that bubba was under the hood.
Race Director
Joined: Jul 2001
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Tom,
The third line has no purpose other than to bypass fuel and avoid vapour lock. The vapours/emission system is separate. All Corvettes with a Qjet carn use a 3 port pump (AFAIK)
OP- there's no advantage to using an aftermarket pump. Going from a 3 port to a 2 port is a downgrade.
The third line has no purpose other than to bypass fuel and avoid vapour lock. The vapours/emission system is separate. All Corvettes with a Qjet carn use a 3 port pump (AFAIK)
OP- there's no advantage to using an aftermarket pump. Going from a 3 port to a 2 port is a downgrade.
Le Mans Master
Joined: Oct 2010
Posts: 6,937
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
its not a down grade and a fuel pump can't force more fuel in unless the Carb malfunctions. the third line was for emissions nothing more, and i doubt it keeps the fuel any cooler
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Race Director
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Melting Slicks
Joined: Sep 2004
Posts: 3,226
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From: Northeast
This is from the 78 chassis manual if it helps:
All y-series (corvette) have a fuel pump which has a metering outlet for a vapor return system. Any vapor which forms is returned to the fuel tank along with hot fuel through a separate line. This greatly reduces any possibility of vapor lock by keeping cool fuel from the tank constantly circulating through the fuel pump.
All y-series (corvette) have a fuel pump which has a metering outlet for a vapor return system. Any vapor which forms is returned to the fuel tank along with hot fuel through a separate line. This greatly reduces any possibility of vapor lock by keeping cool fuel from the tank constantly circulating through the fuel pump.
Race Director
Joined: Jul 2001
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This is from the 78 chassis manual if it helps:
All y-series (corvette) have a fuel pump which has a metering outlet for a vapor return system. Any vapor which forms is returned to the fuel tank along with hot fuel through a separate line. This greatly reduces any possibility of vapor lock by keeping cool fuel from the tank constantly circulating through the fuel pump.
All y-series (corvette) have a fuel pump which has a metering outlet for a vapor return system. Any vapor which forms is returned to the fuel tank along with hot fuel through a separate line. This greatly reduces any possibility of vapor lock by keeping cool fuel from the tank constantly circulating through the fuel pump.
The emissions aspect of capturing fuel vapours from the tank and carb is taken care of by the charcoal canister and associated plumbing on the drivers side of the car. This system uses a third line also running down the drivers side of the frame and is not interconnected with the fuel supply/return lines on the passenger side.
Corvettes with Q jet carbs generally have the three port pumps, those with Holleys have a two port pump. All C3 Corvettes have a charcoal canister.
Advanced
Joined: Mar 2006
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79 fuel pump.
I tried to change 1979 over to an after market furl pump. Had many problems so went back to standard replacement with three hose connections. Had to put a regulator on it because was pumping 9 lbs. Now no problems.
Melting Slicks
Joined: Sep 2004
Posts: 3,226
Likes: 667
From: Northeast
Previous owner put this Holley fuel pump on so I know no difference.
http://www.summitracing.com/parts/HLY-12-327-11/
Been on the Dyno (104 mph) & dragstrip plus all around driving and have not experienced any problems. Perhaps ignorance is bliss.
http://www.summitracing.com/parts/HLY-12-327-11/
Been on the Dyno (104 mph) & dragstrip plus all around driving and have not experienced any problems. Perhaps ignorance is bliss.
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Joined: Jan 2011
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I totally agree. I am still going to put a Holley Fuel Pump with 2 ports. Call me hard headed but I like the looks and blah blah blah. Worse case scenario I change it back doesn't it need to be really hot for vapor lock to occur?
