Can anyone give a description of why this is needed. I've been trying to to do some reading on a fuel return line but haven't had any luck finding much info. first off where does the fuel return from? I'm not sure if this aids anyone in answering my question but my car is an 86 442 I have a sump gas tank and will be running -8an lines the fuel pump is holley blue and the carb is 750cfm demon w/ electric choke. I found one forum (i think it was a chevelle site) they talked about running the return line to the hose in the sending unit but they mention a couple things like vapor lock and a concern of the fuel returning to the tank being just droped in from the top of the tank or running the line to the bottom of the tank. I'm not sure if this has any relevance but . . . .As always every 2cents is appreciated!

 

ttt ( ordering fuel lines next week. HELP PLS!!! )

 

You run a return style regulator. That does a couple things. 1 it keeps a much more consistent pressure at the carb. 2 it helps keep the fuel pump cool by not making it work so hard with a "back up" of fuel in front of it.

You want the return in the top of the tank. The sump is strictly for flow out of the tank. You should have a rollover vent (with a check ball) on the top as well as a fitting to allow for the return.

 

If you are going to use a Holly blue pump, you had better be prepared for noise. All this return line stuff I feel is up to the manufacturer. I have seen very few blue pumps with any kind of return line. If you are going to return the fuel you would be better off buying a better (quieter) pump. I went from a blue to a 140 Mallory (with no return) and was very satisfied. I currently am running a Magna Fuel that has a return line right after the pump. It's expensive ......but good.

 

My understanding is the reason return lines were originally used was to prevent vapor lock on a/c equipped cars. That could be incorrect, but I read/heard it from several pretty reliable sources. Vapor lock is not an issue with an electric pump. Plenty of guys using a dead head regulator and no return line.

As an aside, modern FI engines run return lines for a different reason. They run high pressure and use a regulator to control it, dumping the un-used fuel back to the tank.

 

Correct, though it's not just A/C cars but any cars with elevated underhood temps. Keep in mind that a mechanical pump is "self regulating" in that as the float closes the needle and seat in the carb, the residual pressure in the line between the pump and carb causes the diaphragm in the pump to stay in the extended position, which prevents the pump from moving any fuel even though the lever is still riding on the eccentric. If this didn't happen, the pump would continue to increase pressure in the line and override the needle and seat, flooding the carb. Once the diaphragm causes the pump to stop moving fuel, underhood temps heat the fuel, causing vapor lock. Fuel return simply bleeds off flow from the pressure side of the pump and returns it to the tank. This allows fuel to keep moving even if the needle and seat are closed in the carb. The constant cycling of fuel through the lines carries away the heat and prevents vapor lock.

 

Thanks i was just reading and ran across a couple of articles that mentioned them but if its not needed i'll x it off my list then. So would it be safe if i blocked the return inlet which has a filter on the tanks inside and another line that ends at the top of the inside of the tank? My problem now is i purchased a sending unit (spectre) from rockauto which has a brass looking pin on top its the only electrical piece on the top of the outside of the unit and on the otherside(inside of the tank) is wired to the float arm. well what type of connector would i put on this as it has no threads at all. I'll try to post a pic if possible. thanks