[Will]

Had some bad fuel starvation/percolation problems with the Carter mechanical pump in my '72 Formula. The car originally had a return line (A/C car) but I capped it off since the Carter pump had no return line provision.

As soon as the car would get warm it would start falling on it's face at the top of 2nd gear. Also, when working on the carb in the pits you could see bubbles coming through the inlet valve, which told me the fuel was boiling in the lines somewhere.

I had already planned to convert to an electric pump, but didn't have all the pieces yet and didn't feel like dropping the gas tank all the way out to modify the pickup, so instead did the following:

Installed a Mallory 4-port regulator with return provision between the carb and pump. Hooked the return line output up to the factory return line.

Wrapped the fuel lines with insulator on the passenger side anywhere they came near the headers.

Formed my own U-bend fittings for the fuel pump instead of using brass 90-degree fittings.

Wrapped the muffler and passenger side tailpipe in a sandwich of 1" thick ceramic wool furnace insulation and aluminum sheeting, held in place with hose clamps. Did this because the fuel lines were only an inch or so away from the muffler and very close to the tailpipe in this area.

Installed a VDO fuel pressure gauge mounted to the cowl so it's readable from the driver's seat through the windshield.

Also made some mods to the carb (Q-jet) at this time, including a bigger Ecelbrock inlet valve and richer secondary rods.

Next time out at the track, no fuel starvation problems, no fuel percolating into the bowl through the inlet valve even though the temps were higher that time out.

Still, the fuel pressure would drop to 2 psi by the end of the track, indicating a restriction somewhere in the system. Maybe the sock on the pickup? The delivery and return lines were all brand new SS 3/8" and 1/4", just like factory.

In any case, it shows that vapor lock problems can be solved by insulating the lines and the exhaust components where they run near the fuel lines. A return line is also a very good idea as it allows the fuel to constantly circulate through the lines, so it doesn't tend to boil as easily.

-Will

[KS circutguy]

Been their done that Will,I believe its the pump,I changed to a carter electric w/14psi and a regulator w/ a return line..
No more lose of fuel pressure or vapor lock.
Steve.

[This message has been edited by KS circutguy (edited 08-31-2001).]

[70 goat]

I got some steam pipe insulation coming from work to put around my fuel lines and the header.Lets see what this does.I hope the insulation is rated high enough to take the heat.Thanks again for the input.


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[carbking]

One can still have a return line even if your fuel pump has no provision. Your local auto parts store should have a 'buyers guide' with illustrations for inline fuel filters. Pick one with a 'vapor return line' that will work with your installation (5/16, 3/8, etc. line size), and can be made to fit directly before the carburetor. Typically, the vapor return line will be one size smaller than the fuel line. This restriction allows the carburetor to have first shot at the available fuel. If your vehicle does not have a return line at the tank, generally a good solution here is to remove one of the bolts holding the tank sending unit, chuck it up in your lathe, and drill a hole endways through the bolt. Now sweat in a piece of copper tubing after using half of a double flare. Now you can use a short piece of neopreme fuel line as a connector. The return line is more useful on a street car, where total rerouting of the lines is more difficult that for a race car. Not only does the return line minimize vapor lock problems, it also provides cooler fuel to the carburetor. Jon.

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Good carburetion is fuelish hot air.