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Topic: vapor return line 390-427

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vapor return line 390-427 (1/6)
7/5/13 7:35pm

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

My new engine is ready a 390, 427.

The builder put on a fuel pump that has one outlet to the carb. and two prongs in which one would be for the inlet fuel line from the gas tank , the other prong is supposedly for the vapor return line from the tank. This is what I was told. I am thinking he gave me the wrong fuel pump. The engine is not in the car but on a stand.

The original engine in my 68 was a 427, 435 HP and did not have a return line from the gas tank. So I plan to put in a new gas tank with a vapor fuel outlet. But what I can tell from the assembly manual on the 68, the vapor line goes from the gas tank to the fuel filter and not the fuel pump.

This fuel filter has and inlet and outlet plus a prong to attach the vapor line.

So what I can tell is I need a fuel pump that has an inlet from the tank and then an outlet which goes to the filter and on to the carb. And no other inlet for vapor.

Does this sound correct.

Did the builder put the wrong fuel pump on my 68??? Or can you just put a vapor line into this fuel pump and use a filter that does not have the outlet for the vapor line??

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Re: vapor return line 390-427 (2/6)
7/6/13 7:15am

Adams' Apple

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20170

The "extra" port on the pump is not a vapor line....it is a fuel return line. Whether on the pump, or on the filter, it accomplishes the same thing. Returning un-used fuel back to the tank. It is supposed to help with the vapor lock problems, since keeping the fuel moving keeps it from getting hot enough to turn into vapor, but.....

Depending on how you want the car to look, you can simply put a plug on the spare line on the pump. If you are going for a "correct" look, then you will need to get a pump without the return line. Since your car was originally a bb, and it does not have the return line on the frame, there's no sense in trying to plumb in a new line front-to-rear just because the pump is like that. It's much easier to get the "correct" pump, OR just plug the line off on the pump. imho.

Plugging the extra line on the pump will not hurt it.....it's done all the time.

hth

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Re: vapor return line 390-427 (3/6)
7/6/13 9:06am

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

The way I understand, and my 68 does not have the return line is the 427 435 HP did not have a return line and neither did the L 88. But the 390 427 did have a return line along with the small blocks from the factory. I don't know the reason behind all of this!

I have a 327 in the car right now, and I have always had vapor lock no matter how much insulation I put around the lines and elsewhere. Probably because it did not have a return line. With the temp soon to be over 100, I am trying to prevent vapor lock with this new engine is the reason.

It is not so important to make it factory correct as it is to solve my vapor problems. I know it will be a PIA to route the new line and change out the gas tank but I am sick of the vapor problems, and with the new hot engine this could be the problem again.

Any other suggestions??

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Re: vapor return line 390-427 (4/6)
7/7/13 8:33am

knotacare
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Newark, DE - USA

Vette(s):
1968 Conv, 454HO,500HP-600TQ, TKO-600,3:70 HD rear,hotrod air, custom paint & suspension,1973 Ruby Red,T-top, 383 Stroker, TK)-500,frame off restro, 1967 Dodge Coronet, 340 stroker to 406, Dana 60

Joined: 7/26/2004
Posts: 466

I solved the problem on my 68 (on hot days) I put in 2 spal 7" fans on the frame behind each frt tire. They pull down & get rid of lots of heat in the engine. Also a vented fuel cap is needed. Forgot to add I'm running a modified 454 that put out mucho heat.

Alan

|UPDATED|7/7/2013 9:33:03 AM (AZT)|/UPDATED|

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Re: vapor return line 390-427 (5/6)
9/22/24 3:33pm

Mark M
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Nixa, MO - USA

Vette(s):
1980 - 350 Black 5 speed

Joined: 9/22/2024
Posts: 1

Did you add the thermostat to turn fans off when not needed? Are the fans on the finder wall or are suspended?

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Re: vapor return line 390-427 (6/6)
9/23/24 4:25am

Boy this is an old post.... I installed the fans on the frame blowing down and the switch is on the dash which I operate manually. Usually only at a stop light or in traffic, they really pull the heat out and still working all these years

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