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post #1 of (permalink) Old 10-09-2002, 09:02 PM Thread Starter
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engine question

i just installed a chevy 350 from a k5 in my cj7. its a car bed engine with an edlebrock 1406(?) 650 cfm carb. im running a standard holley red mechanical fuel pump. the jeep originally had a fuel filter with one inlet and 2 outlets. one for the carb the other for fuel return. the chevy fuel filter has only one inlet and outlet. the jeeps carb was a 360 cfm for the 258 inline 6. does the 350 need some sort of furl return line? if so houw would i hook one up?
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post #2 of (permalink) Old 10-10-2002, 08:02 AM
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Re: engine question

To prevent vapor lock and since the return line is already there get a duel output fuel filter and run the top smaller outlet to the return line.
After switching to a filter with a return line I found that I had to ensure that the return line on the filter was always higher than the line to the carb and I had to re-adjust my pressure regulator to get the psi back up to 5.5 which is what my edle 600 likes best. I'm doing this on a 360.
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post #3 of (permalink) Old 10-10-2002, 09:59 AM
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Re: engine question

What exactly do you mean when you say it has to be higher? Do you mean that the return line runs back to the tank farther up from the road/trail? Or are you only refering to the under hood plumbing of the lines?
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post #4 of (permalink) Old 10-11-2002, 12:10 PM
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Re: engine question

Higher as in above, meaning if you were looking down at the outlines you would see the return line above the carb line. Enclosed is a realllly crappy representation. The box is the filter, return line outlet is above the carb line
] {-- return line
[filter[-- carb line
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post #5 of (permalink) Old 10-11-2002, 12:15 PM
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Re: engine question

Excuse my ingorance on this subject, but I have never had a problem with vapor lock. How does a return fuel line on a Carbed motor prevent vapor lock and what exactly causes vapor lock?
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post #6 of (permalink) Old 10-11-2002, 01:17 PM
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Re: engine question

Vapor lock is when the suction side of the pump lowers the pressure below atmospheric pressure and when combined with high temperatures, lowers the boiling point of the fuel. The fuel turns to a vapor in the line before the pump and the pump sucks vapor but no fuel. It's mostly a problem with the pump in the engine compartment, either electric or mechanical. If the pump is in the tank or next to it (below the fuel level) it shouldn't be a problem. The reason the return line solves vapor lock is it lets fuel continually flow through the system so it doesn't have time to 'stop' before the pump and warm and vaporize. It just depends on the routing of the fuel lines, heat sources and where the pump is.
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