[brian71Formula400]

I have a new tank for my 71 Formula 400. the engine is a 1975 400, so there are a few differences. the fuel pump mounted previously on the engine has 3 total lines- one is supply from tank, one is exit line to carb, and a third that is (at least i thin) a return line for unused fuel.
I do not have a return line connection on the new fuel tank (non EEC version is what i bought).
so, my dilemma is whether I should buy a new fuel pump or plug the return line hose (and use the existing pump). of course, this is assuming i do not need a return line (not sure).
if anyone has a suggestion, please post it.
Thanks in advance!
Brian

 

[taman76]

I believe you will need that return line if you continue to use the mechanical pump.

The easy fix is to install an electric pump if you aren't concerned about keeping it totally original looking. not that anyone really will ever look under the car to see where your fuel pump is.

 

[xxcody2gunsxx]

if you plugged it you might run into a vapor locking problem and other problems .

I had a similar problem with my 67 camaro . I got a electric pump with a regulator "holley performance" and that fixed it . but those electric pumps can be alittle loud. .

 

[ponchonutty]

I found my '70 has a pump with 3 lines out. The return line was crimped shut. I haven't had any problems either with leaking or drivability.

 

[Glenn Lever]

Get a pump with the three lines, electric is loud and you do not need the capacity of an electric for stock of mild proforamce engines.

You are correct the third line is for a bypass for unwanted/needed/ extra fuel.

Two line mechanical pumps may not be able to supply enough fuel.

 

[brian71Formula400]

OK, so if I go ahead and use the fuel pump that's on it, (3 lines), I will need to run a return line to the tank. the sending unit i purchased does not have a place to attach (the return line) to the gas tank. should I add a hole to the sender and add a grommet/fuel fitting? I dont feel comfortable drilling into the tank, as it is a brand new one.
Thanks for all of your help guys and girls!

 

[GaryDoug]

OK, so if I go ahead and use the fuel pump that's on it, (3 lines), I will need to run a return line to the tank. the sending unit i purchased does not have a place to attach (the return line) to the gas tank. should I add a hole to the sender and add a grommet/fuel fitting? I dont feel comfortable drilling into the tank, as it is a brand new one.
Thanks for all of your help guys and girls!

IMHO, I would not add the return line, and certainly would not modify the tank to do so. My 1970 Formula 400 did not have the return line, and the mechanical fuel pump had just the two fittings. You should be fine by plugging the return line at the pump or buying a two-line replacement pump. The returrn line was added to the design in order to combat vapor lock in vehicles operating in warm climates, using the a/c, and/or idling (in traffic) for long periods, The return line keeps the fuel moving so that the heat under the hood doesn't boil it in the lines. I regularly used the a/c on my Formula (in Florida) and never had a problem for 150k miles of daily use. But if you have problems with vapor lock (stalling or hard starting in hot weather). you may later want to add the line somehow, but will probably have to change the tank to do so.

 

[WHITE-68]

Gary is right, you should just install a standard 2 line pump, and you should be fine. They added those 3rd lines in the 70's as part of the smog systems to try and remove unused fuels. In your case you don't need as the tank you have does not support it and I really don't think you have smog equipment installed on a 70. I run a mild performance 455 and have no problems with my 2 line mechanical pump.

 

[Glenn Lever]

If your sending unit does not have the third line, do bother withit in a stock application.

Third line was not for smog, it was designed to keep the fuel cool, also the pumps with the third line have higher capacity and the excess fuel must be returned to the tank.

 

[GaryDoug]

IMHO, I would not add the return line, and certainly would not modify the tank to do so. My 1970 Formula 400 did not have the return line, and the mechanical fuel pump had just the two fittings. You should be fine by plugging the return line at the pump or buying a two-line replacement pump. The returrn line was added to the design in order to combat vapor lock in vehicles operating in warm climates, using the a/c, and/or idling (in traffic) for long periods, The return line keeps the fuel moving so that the heat under the hood doesn't boil it in the lines. I regularly used the a/c on my Formula (in Florida) and never had a problem for 150k miles of daily use. But if you have problems with vapor lock (stalling or hard starting in hot weather). you may later want to add the line somehow, but will probably have to change the tank to do so.

oops,... I meant to type "change the sending unit" instead of "change the tank". And that is assuming the other sending unit would fit your tank.

BTW.. when I was in the military, I saw motor-pool techs modifying the base vehicles to connect the fuel return line to a T-fitting on the carb instead of at the fitting on the pump. They said it worked better than the original setup because it also re-circulated the fuel in the pipe to the carb as well. This was in Libya where the temperatures frequently rose above 120.

 

[Alan70]

This is what I did. Ran a new tank with a vented cap and had a sump welded to bottom of tank with two outlets with 1/2 inch line into one big filter and a electric pump to carb with a regulator and ran a return line back thru the stock line back into thru the top of tank using only one line back into tank. thus this keeps any hot or unused fuel back into tank and cool fuel out bottom of sump and when I stepped on it no problem with fuel because it all dumps into sump and you don't need a cell for a tank. Now I know you are not going this way but if you do and add nitrous one day you will have plenty of fuel going up front and no issues. I took that smog tank out with the vap system all together on my 70 and it worked great running this way with the vented cap. It will not hurt to run a return line. Hot or cold my system worked awesome.

 

[brian71Formula400]

Thanks for the help-
I went and ordered a 2 line fuel pump, that will solve the problem. I need to use a vented cap from my understanding, as there is not a vent in the tank from what I see (nor is there one on the sender).

Brian

 

[Alan70]

If I recall it is a 74 to76 cap that fits but if you have tank still off bring it down it took me a few to find it. some reason the new tanks take a diff cap.