MC 4350 carb issues - JeepForum.com

 
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post #1 of 12 Old 05-04-2011, 11:39 AM Thread Starter
andy_mitch92
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MC 4350 carb issues

I figured I may have slightly better luck asking this question in the FSJ section.

Anyway I just replaced the old 258 with a 4bbl 360 from a 77 J-20 truck. The issue I am having is if I let the jeep sit for more than a few hours it seems like the fuel will drain out of the carb somehow. I can go and take the fuel like off the fuel filter and there is maybe a few ounces in the filter itself and none in the feed hose from the pump.

Did Jeep install electric fuel pumps in FSJ's inorder to pre-prime the fuel system? If I pour about a thimble full of gas down the carb the motor fires up first crank and runs great when fully warmed up.

The 258 had the fuel feed line from the tank on the passenger side and of course the pump is on the driver side on the V8 so I ran some hard line up under the radiator then back down the driver side to get it in the correct location. Could this cause the gas to boil off after it is just sitting?

The carb has a fresh rebuild. I replaced all the rubber lines from sending unit, and every other one I could find. I dont see any place where gas is leaking out of the carb. The fuel pump is new. Kind of lost as to what is causing this.

Any insights?

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post #2 of 12 Old 05-04-2011, 02:59 PM
Dngrs1
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Make sure the return line on the filter is in the "12 o'clock" position.
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post #3 of 12 Old 05-04-2011, 05:15 PM
pleontks
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I also have this problems on my j10 360 and my Gremlin 258. I run inline electric pumps now. I trun the key on for a second and let it prime, and then I'm good to go.

Beauty is in the eye of the jeepowner.
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post #4 of 12 Old 05-04-2011, 05:22 PM Thread Starter
andy_mitch92
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Quote:
Originally Posted by Dngrs1 View Post
Make sure the return line on the filter is in the "12 o'clock" position.
Yup. I know to do that

Quote:
Originally Posted by pleontks View Post
I also have this problems on my j10 360 and my Gremlin 258. I run inline electric pumps now. I trun the key on for a second and let it prime, and then I'm good to go.
Darn. Kind of figured. Guess I will have to shop around this summer at some junkyards for a TBI system.
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post #5 of 12 Old 05-04-2011, 05:28 PM
pleontks
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I meant to also mention....
Did you play with the venting system (charcoal canister and stuff)? I removed mine and had to put a venting gas cap to cure the vaporlocking that developed.

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post #6 of 12 Old 05-04-2011, 05:31 PM Thread Starter
andy_mitch92
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Quote:
Originally Posted by pleontks View Post
I meant to also mention....
Did you play with the venting system (charcoal canister and stuff)? I removed mine and had to put a venting gas cap to cure the vaporlocking that developed.
Well I hooked it up how I *think it should be. I ran a line from the vent off the carb bowl to one of the ports on the canister. I was kind of wondering if this could have been a problem. Like the gas tank sucking gas back out the return line or something crazy like that.

Guess I will have to crack the gas cap next time I go drive it and listen to for any hisses.
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post #7 of 12 Old 05-04-2011, 05:37 PM
pleontks
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I just ran out and checked my truck, I do not have the return line connected.
No vents, no charcoal canister.
Electric pump, and vented locking gas cap. Fill tube, feed line.

That's the entirety of my fuel sytem. No complaints at all.

Goo luck

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post #8 of 12 Old 05-04-2011, 06:27 PM Thread Starter
andy_mitch92
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Okay so I just ran out to pull the Jeep back into the garage. It started just fine after sitting for 3 hours making me look like a lier.

Well I decide to let it idle for a few min then I pulled the fuel cap. No hisses or anything, but I heard gas coming back in at a pretty high rate from the return line. So I go shut it off and gas keeps flowing thru the return for a good 30 seconds. I wonder if it is some how syphoning the gas out of the filter and possible bowl after I shut it down?
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post #9 of 12 Old 05-04-2011, 09:39 PM
pleontks
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I would believe that.

Is your roll-over valve hooked up? Do you have one? Mine is in the garage. It was one extra thing I didn't want to figure out.

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post #10 of 12 Old 05-05-2011, 10:29 AM Thread Starter
andy_mitch92
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Quote:
Originally Posted by pleontks View Post
I would believe that.

Is your roll-over valve hooked up? Do you have one? Mine is in the garage. It was one extra thing I didn't want to figure out.
Yeah I have everything in the back by the tank hooked up like stock. I would love to keep all of it there too just incase because I DD the Jeep a lot.

I went to start it today after I got out of class... cranked it off and on for about a min, no start. Well I went back and tried it 5 min later and it fired right up.... idk what is going on.
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post #11 of 12 Old 05-05-2011, 06:13 PM
pleontks
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seems like it's vapor locking. Cold when you parked and warm out when you tried to start her?

My plan was to eliminate everything, and then add them back in 1 by 1, but when I got everything out, the prob went away.

Got a compressor? Try blowing out all the lines. Vents, return, supply.
Is there crap in the tank? Something could be blocking the line, and then floating away.
Did you recheck all your clamps and make sure they're all tight? The cheaper clamps tend to come loose. Could be a small enough leak to let air in, but not gas out.

The 258 had the fuel feed line from the tank on the passenger side and of course the pump is on the driver side on the V8 so I ran some hard line up under the radiator then back down the driver side to get it in the correct location. Could this cause the gas to boil off after it is just sitting?
After re-reading, this seems like it might do it. Try just getting some rubber fuel hose and bypass the line by the radiator. Drive it for a day and see. I had to lengthen the hose on mine from the frame to the carb when I eliminated the manual pump to get the line away from the exhaust.

Beauty is in the eye of the jeepowner.
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post #12 of 12 Old 10-25-2013, 12:54 AM
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I bought a New billet aluminum Insulator for my 1977 j10 4350 MotorCraft Carburetor and OEM intake manifold with top and bottom gaskets from these guys and it works better than anything Jeep ever produced, However it was not cheap.
Building 5 Area 51 Calibration Specialist "B5A51@yahoo.com"
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