Vaporlock fuel


Well-known member
Apr 12, 2015
Cincinnati - Middletown OH
I have sbc 383, dual elderbrock 500 carbs. I believe I have vapor lock issue as I am understanding the symptoms. Not running well when it gets hot, not consistent idle, etc. Won't start when hot.

I found a vapor lock filter that has a return line to the tank and it seems to have helped but I have not drove it very far to make sure.

I was told my carbs also need adjusted at 5 to 5.5 psi. I just put a gauge on the line and Im pushing 7.

Here is my question, do I need the vapor lock filter and a fuel regulator or can I just use a regulator with a return hose to the tank?

In addition, where should the filter/regulator be positioned? I want to make the engine a clean as possible.

I running a holly mechancal pump.

Thanks in advance for any help you guys can provide.


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Garage Monkey
Staff member
Mar 5, 2008
Right here
I'm not familiar with the filters and regulators with return lines. Do they separate vapor from fuel? If so I think that would work.

Might help to insulate the fuel lines from heat also.


Well-known member
Nov 5, 2011
Vapor lock was an issue for me in Orlando with the zz502. I did two things that really helped. A return regulator, this keeps the fuel circulating back to the tank, so temperature stays lower. I mounted it higher than the valve covers but not over the engine. I have an electric fuel pump. Second was a pusher fan in front of the rad that ran continuously.

Also cut holes in the l88 hood and doubled the size of the holes in the side of the fenders (behind the front tire).


Well-known member
Jul 16, 2012
Seattle, WA
with EFI, regulators go after the supply (in the return line), but on carbs, regulators usually go before to maintain a steady supply of fuel and not overwhelm the needle valves. Is the regulator a bypass style? You've done everything most do to eliminate vapor lock - so is it possible that your regulator is stuck open?
where did you run your lines? did you just bypass the mechanical pump?

with that said, have you adjusted the pressure at the pump? Holley electric pumps can adjusted at the pump to 3-5 psi output

so other thoughts.
not starting when hot can be a number of things that are unrelated to vapor lock - most notorious is too high of float level then fuel gets pulled into the motor through the vents, second is the pressure spike when you shut the motor off allows fuel to overcome the needle then flood the motor. Does the motor shoot black smoke when you do get it started? time, also, fixes this problem because the fuel evaporates ....