Fuel return line size?
Thread Starter
Instructor
Joined: Apr 2000
Posts: 165
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From: Vacaville California
Fuel return line size?
What size is the stock fuel return line that runs on passenger side next to the main supply line?
Would there be any advantage in routing the fuel return line from near the carbureter back to the tank vs. running it from just the pump back to the tank?
Thanks for any help.
Would there be any advantage in routing the fuel return line from near the carbureter back to the tank vs. running it from just the pump back to the tank?
Thanks for any help.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Originally Posted by singedfur
What size is the stock fuel return line that runs on passenger side next to the main supply line?
Would there be any advantage in routing the fuel return line from near the carbureter back to the tank vs. running it from just the pump back to the tank?
Thanks for any help.
Would there be any advantage in routing the fuel return line from near the carbureter back to the tank vs. running it from just the pump back to the tank?
Thanks for any help.
NO, the way I understand the f/p and the lines is very similar to fuel injection, in that the surplus fuel is returned to tank,
the fuel pump is actucated by a lever off the cam drive, so it has peaks and valleys, pressure wise, just like valve openings and closings, to the peaks are pressure releived and returned to the tank, this to keep the floats/seats from being forced open during idle or light throttle operation...it's a pressure relief system, really....
now I"m not sure why some very early cars didn't need/have such a system from the factory....maybe a chem change in gas?? I dunno....
you block that return line with say a vice grip, and watch the carb flood out shortly after....
pulling off the top of the carb is highly unreliable in that it's not a pressure area, and so would be too dependant on cornering, braking,...car dynamics....and of course....
leaking....damn carbs have enough problems with that, without adding more complications...
GENE
Pro
Joined: Sep 2004
Posts: 595
Likes: 0
From: Boston MA
Originally Posted by mrvette
NO, the way I understand the f/p and the lines is very similar to fuel injection, in that the surplus fuel is returned to tank,
the fuel pump is actucated by a lever off the cam drive, so it has peaks and valleys, pressure wise, just like valve openings and closings, to the peaks are pressure releived and returned to the tank, this to keep the floats/seats from being forced open during idle or light throttle operation...it's a pressure relief system, really....
now I"m not sure why some very early cars didn't need/have such a system from the factory....maybe a chem change in gas?? I dunno....
you block that return line with say a vice grip, and watch the carb flood out shortly after....
pulling off the top of the carb is highly unreliable in that it's not a pressure area, and so would be too dependant on cornering, braking,...car dynamics....and of course....
leaking....damn carbs have enough problems with that, without adding more complications...
GENE
the fuel pump is actucated by a lever off the cam drive, so it has peaks and valleys, pressure wise, just like valve openings and closings, to the peaks are pressure releived and returned to the tank, this to keep the floats/seats from being forced open during idle or light throttle operation...it's a pressure relief system, really....
now I"m not sure why some very early cars didn't need/have such a system from the factory....maybe a chem change in gas?? I dunno....
you block that return line with say a vice grip, and watch the carb flood out shortly after....
pulling off the top of the carb is highly unreliable in that it's not a pressure area, and so would be too dependant on cornering, braking,...car dynamics....and of course....
leaking....damn carbs have enough problems with that, without adding more complications...
GENE
I had the same question. So if you can not route the line from the carb, where should you route the return line from? fuel pump?
The line is 1/4 right?
THanks,
Joe
Racer
Joined: Sep 2000
Posts: 485
Likes: 1
From: Dallas Texas
The return line comes off the fuel pump. Stock fuel pumps will have three fittings for an inlet, outlet to carb, and a return line. Usually aftermarket fuel pumps like Holley only have two fittings; in and out and you have to run a regulator to get the return line.
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
The return line helps to prevent vapor lock. Boiling fuel is a big problem if it's in the suction line as the fuel pump won't suck vapor. By constantly circulting fuel the temp is reduced. It is better to rturn from the carb, but the pump is better than nothing.
Yeah, I think it is 1/4".
Yeah, I think it is 1/4".
