68-69 Dual fuel line cars

[Tom B.]

Just researching some reference material and came across this. What are "the dual fuel line cars"? A reference in the 68-69 JM (page 98) was made to the fuel supply line clamps. Single fuel supply lines use (4) green colored spring ring clamps, two each at the fuel pump and fuel tank. **For the dual fuel line cars**, the fuel return hose at both the fuel filter and tank is secured with small tower clamps in 1968 and orange spring clips in 1969. Are they referring to dual fuel lines at the engine or what? TBarr #24014

[Duke W.]

Re: 68-69 Dual fuel line cars

"Dual fuel lines" could be a misnomer and refer to a vent line that was part of the evaporative emission system. I recall evap emission systems became mandatory circa 1970, but it could be that California cars had an evap emission system before they were required for 49 state cars.

Duke

[Chuck G.]

Re: 68-69 Dual fuel line cars

Rochester Quadrajet equipped cars used the vapor return line...thus the "dual fuel line", while Holley 3x2 cars used a "single" line...i.e. no vapor return line. A poor choice of words, but if you look at four barrel quadrajets vs. 3x2 barrel Holleys, you'll see the difference....2 lines on four barrels, 1 line on tripowers. Chuck

[Tom B.]

Re: 68-69 Dual fuel line cars

Thanks guys. Of all the (few) Corvettes I've had, they've all been Holley carbed. TBarr #24014

[Joe L.]

Re: 68-69 Dual fuel line cars

Tom-----

Chuck "hit the nail on the head".

[Bob Lanham]

Lack of 2nd line

Could the lack of the second vapor line cause pressure build up in the carb and cause leaking? What is the purpose of the vapor line? My 69 doesn't have the line and I want to know how it should be before I replace the carb and have the same problem. Thanks

[motorman]

Re: Lack of 2nd line

if you remove the return line and block the outlet from the pump you get a big increase in fuel pressure and this will cause flooding. i have used this trick to get home when a fuel pump went south and blocking the return line will increase the pressure enough to get you home. these pumps have 3 fittings instead of 2 like std pumps. i have also seen these return lines to the tank plug up with rust/dirt and cause carb flooding.

http://clemz9@hotmail.com

[Joe L.]

Re: Lack of 2nd line

Motorman-----

Actually, I believe that you're thinking of the 70+, "long cannister" fuel pumps. These pumps did have 3 fittings----inlet, outlet, and return. For 1968-69 fuel pumps for all engines had only 2 fittings----inlet and outlet. For 68-69 with Rochester carburetors, the return line went from a nipple on the top of the GF-432 fuel filter, down a metal line which ran essentially parrallel to the fuel pump-to-fuel filter line, and connected to the frame return line at a point near the frame fuel line outlet at the fuel pump.

This line was essentially installed to prevent fuel vapor lock conditions, but I believe that its removal on 68-69 models might also contribute to flooding conditions as you described.