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Old May 5th, 2013, 09:11 PM   #1
CHEROKEEMUDMAN01
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Default fuel prob vapor lock please help

i am having prob with under hood temps getting hot enough that i cant touch the carb. the motor itself is around 190 to 195. after running for a while and building up heat the motor will start missing and then will stall and wont restart till it cools down and then will fire right up.

here is what i have. fuel cell vented and no rollover valve, 6an braided line running to earl filter then to mech fuel pump(holley high volume), then to carb in steel line (holley 670 truck avenger). at carb i am between 4 to 6 psi.

i did try opening gas cap when it started to act up last time and it didnt have a vacuum sound so i think venting is not the issue.

so i have been told its fine dead heading a mech pump with no return but i wondering if putting a return line in would help with vapor lock?

if i am going to install a return what size line to i run back to the 8an tank connection?

can i do this with a dodge fuel filter with the little nipple off side or shound i buy a regulator with a bypass and go that way?

is there anything else i can do to help with the vapor lock?

sorry for the long post i just am at a loss and dont know what is correct way to fix this prob. i did wrap headers and put vents in hood which helped but under hood temp is just to much in the cherokee with the v8. going to swap a alum intake with a bit more of higher rise in motor instead of the CI one im running now to help keep carb itself off the hot motor. carb draws air from cowl hood and is sealed off from motor bay air .

even might try a carb heat deflector if anyone thinks that may help
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Old May 5th, 2013, 09:44 PM   #2
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Best way would be a elec. pump in the tank or near the tank and then the regulator close to the carb.

How is the line going to the pump routed?

The line to the mech. pump is most important to keep away from heat, fuel boils in that line and the pump can't pull fuel.
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Old May 5th, 2013, 10:14 PM   #3
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it runs down the inside cornor of unibody close to floor pan on passenger side. then i turned it straight into mech pump. i am going to put some heat shields on it bo try to help deflect heat. steel line from pump to carb though is almost touching motor all the way to carb and is spaced with insulated rubber 1 hole straps.
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Old May 6th, 2013, 06:09 PM   #4
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anyone?
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Old May 7th, 2013, 06:49 AM   #5
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Running a return line will help with keeping the fuel cooler. That is why they started to do that from the factory years ago. Does your fuel pump have a return line fitting on it or not? I dont know about the dodge filter you are talking about. As far as return line size, I would say smaller than the supply line.
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Old May 7th, 2013, 02:03 PM   #6
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i am basically running a stock mech fuel pump. it dosnt have a return line spot. the fuel filter has a 1/4" line off the side as a return since i cant really think of any place else to tie a return into system. every regulator i look at with a bypass says not for mech pump. any other way to put a return on.

can i put the return line into the 2nd 8an fitting on the sump of fuel cell that i have caped off or does it have to go to top of fuel cell?
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Old May 7th, 2013, 02:44 PM   #7
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For what it is worth, I have dealt with serious vapor lock issue on my CJ-5 with a 304. The stock fuel filter setup uses a return line to reduce vapor lock. When using this type of filter the return line barb must be at the top of the filter. Even with this type filter, and insulated lines and tank, I would still have vapor lock when going down the highway on very hot days. I ran into an AMC guy at a car show that showed me a flap gasket that AMC used on 304's at the fuel pump. The gasket is exactly the same as the normal pump to timing cover gasket, but it has a flap that shields the pump from the heat coming off the coopling system (since everything is right there).

When I got home I insulated the fuel pump with a small sheet of THermatech Heat Shield. Since then I have not had a problem.

It should be noted that my problem stems mostly from running down the highway. It seems to be a result of lower gears making me turn more rpm's, combined with summer heat. WHen I keep the rpm's down I do not experience the problem. Mine was serious enough that it was able to presurize my tank.
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Old May 13th, 2013, 12:08 PM   #8
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Ive had the same problems in the past w/running an amc 401in a willys. Buy a length of heater hose and slice it, slip it over your gas line. Ive also done this to my willys pickup, under the hood where it goes past the manifold and under the floor where it goes past my muffler.
I run 5/16 gas lines but other guys do use 3/8 line instead.
Because i now use an electric fuel pump, i do have a return line.(helps)
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Old May 13th, 2013, 01:05 PM   #9
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i will give that a try with the heater hose. i have been putting off messing with it lately but prob one night this week. going to make up a few stainless heat shields also near muffler to keep that area cool and go from there. i guess with all the stuff in gas now this is becoming more of a common prob from what i have read.
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