Carburetor heat soak or vapor lock?

[Sixpactogo]

I'm trying to educate myself on return line size needed. I'm currently running a 1/4" return and 3 nipple filter with small ID orifice return connection with my Quick Fuel carb. In reading the Aeromotive FAQ, they say that minimizing vapor lock by keeping fuel cool and flowing requires a 3/8" return line for my setup using a mechanical fuel pump. If that's true, why do the 3 nipple fuel filters have the small ID orifice to restrict flow?

With a larger orifice in the return, there is concern of starving the engine by sending too much fuel back to the tank. I have no idea why someone would require a 3/8" return. Mopar design engineers installed the 1/4" return like you have for the very reason of minimizing vapor lock. You should quiz Aeromotive to see if it is a typo.

 

[68 Sport Satellite]

With a larger orifice in the return, there is concern of starving the engine by sending too much fuel back to the tank. I have no idea why someone would require a 3/8" return. Mopar design engineers installed the 1/4" return like you have for the very reason of minimizing vapor lock. You should quiz Aeromotive to see if it is a typo.

This is in the Aeromotive 13301 fuel pressure regulator installation instructions. Now, if you're not using a regulator, then I would agree the return line could be smaller, but with the regulator controlling system pressure, it's supposed to be return line is equal to or larger than the supply line.

 

[68 Sport Satellite]

I have a 1/4" return.

are you using a regulator or no?

 

[dfrazz]

are you using a regulator or no?

No regulator, stock mechanical fuel pump.

 

[Dennis H]

Hold to floor until black chunks come out or get Edelbrock EFI.

 

[68 Sport Satellite]

No regulator, stock mechanical fuel pump.

It seems that a 1/4" return should be fine then, which is what I have. If I ever install my regulator again, I'll need to upsize to a 3/8" return.

 

[old guys rule]

Don't mean to hi-jack your post, but since I'm having the same trouble with heat soak, I figured I'd go ahead and ask here instead of creating a whole new thread. I'm going to put a fuel filter with a return line in but was curious about where at the tank to put the return line. The previous owner had put a fitting in the filler neck for a return line since it used to have a FiTech system on it. Would that still be a good place to plumb it to, or should it go directly to the tank? I guess I should add that I have a Holley fuel pressure regulator (set at about 6psi) just after the mechanical pump with a clear filter in-between it and the carb.

Caution - a clear filter is very dangerous especially if it is glass. Even if plastic they can crack from heat cycling. Both are fire hazards big time. Would hate to see your ride burn to the ground. On a related subject, make sure you have a fuseable link in the harness. Also a classic fire hazard. Dave