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Unread 06-16-2010, 08:44 AM   #1
Registered User
1979 CJ7 
Join Date: May 2010
Location: Colorado
Posts: 1
Fuel Line Confusion

I'm guessing there is a thread about this out there, but I couldn't locate it (I'm a little impatient, especially when I should be working rather than looking at cool Jeeps). Anyway, here's the story: I have a '79 CJ7 that a prior owner dropped a 360 into. It has the hydromatic transmission and quadratrac transfer case, full time 4-wheel drive. I've been having trouble with vapor lock and I believe this is due to the bigger motor and the fact that the transmission is water cooled, so the temp pushes up just beyond 190, even with the thermostat removed. That said, here are my questions:
I was wondering why my fuel filter has two outlets, one of which goes back to the tank?
Is this necessary or can I plug that line and run a filter that just has one outlet dedicated to the carb?
I don't know that this will change my vapor lock issues, and I'm planning to drop the tank and install an electric fuel pump on the frame rail, with new lines to the motor in hopes of solving that issue, but wondered if the return line to the tank was vital to the operation of the Jeep?
Also, I'm planning to get a pump with a range of 4-7 psi, can this be used as a booster for the mechanical pump, or should I remove it and put a block plate on, or do I need a pressure regulator?

Forgive me for the length of this post, I've been trying to solve the problem without help from all you Jeep gurus out there and now that I have realized the error of my ways the questions have become numerous.


Last edited by MSTaylor; 06-16-2010 at 02:10 PM..
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Unread 06-16-2010, 08:56 AM   #2
Mike Romain
Registered User
1986 CJ7 
Join Date: Nov 2007
Location: Off the Grid in Chester Grant, Nova Scotia, Canada
Posts: 18,090
Well 190F is really cold for starters, my t-stat starts to open at 195F and is not fully open until 218F according to the FSM.

The gas filter sits level and has two outlets, a center one that goes to the carb and 'top' one that goes to the return line. This is to prevent vapor lock. On a hot shutdown, any gases produced get blown back to the tank off the top of the filter rather than vaporlocking the gas line. A gas line too close to the exhaust can aslo boil it vapor locink things.

Now if you are plain starving for gas, that is a different issue which could be as simple as someone forgot to hook up the gas tank vent when the engine was swapped or even a dirty air filter on the gas tank vent. These can put a vacuum on the gas tank making it starve for fuel. The fast test is to just open the gas cap next time it misbehaves and see if that fixes it. The rubber gas lines are also 'not' compatible with the crap they put in the modern gas so go bad, crack and leak which will again starve the engine. they are suction lines, so you don't see drips, just stains on them when cracked.
86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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fuel pressure regulator , fuel pump , fuel system

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