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Unread 04-02-2012, 09:56 PM   #1
pman
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Bad Juju with fuel pumps...priming issues RESOLVED

All this chatter yesterday with people and their priming issues; it must be contagious. Wife was anxious to take the Jeep for a spin today. She shows up 10 minutes later walking to the house. Ooops! (I'm in the process of rebuild the entire vehicle, but it's been running/driving fine) I get the the Jeep and look down the carb and see its not getting fuel. Drag it back to the house, bowl is dry, line from fuel pump to Carb is dry, and line at the bottom of the fuel pump going to the tank is dry.

Here's what I'm working with-
304 V/8 with MC 2100 carb
BRAND NEW tank, sending unit, filler and vent hoses

Here's what I've done tonight-
-Disconnected line at tank and at the bottom of the fuel pump; blew air through the it and confirmed it is now clear.
-Gently shot a little air from the fuel line (below fuel pump where I disconnected it) back to the fuel tank. Heard some noise in the tank but can't 100% be sure I heard bubbling.
-Put 5 gallons of fuel in there day before yesterday. I've confirmed there's still probably 4 1/2 gallons or so left.
-Put a hand pump on the disconnected end of the line (from the bottom inlet side of the fuel pump going BACK to the tank) and struggled to pull gas up through the pump. Literally the clear rubber line would collapse before it would pull any fuel. Question: Should it be that hard to draw fuel through the line from the tank?? I removed the gas cap to see if this would release the fuel. No go.

I also can't blow on the gas line back to the tank. Shouldn't I be able to blow on that line and have it reach the fuel sock and blow bubbles?

I hooked everything back up and will try to prime/crank it tomorrow morning, in hopes that blowing the lines may have cleared something out. I'm just concerned that my hand pump couldn't pull fuel. The sock, sending unit, EVERYTHING is brand new back there.

Jeez I'm long-winded. Anyone have ideas?? I'll update what happens tomorrow. Maybe the fuel pump diaghram is shot and its just a "manlier" pump than my cheapo hand pump. I'll tell you this, there are NO air leaks.

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Unread 04-02-2012, 10:19 PM   #2
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Yeah, the line should be clear. You should be able to blow air through the line. If it is collapsing when you apply vacuum, then it is plugged. Since everything is new have you thought to make sure it isn't pinched somewhere... between the tank mount, frame, etc?
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Unread 04-02-2012, 10:26 PM   #3
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Skerr, thanks for the reply. Yes, checked with a flashlight where the line runs off the sending unit and it's not pinched anywhere. I blew air into the tank about a foot from the outlet on the sending unit, and blew air through the remainder of the line leading back to the fuel pump (used very low psi compressed air). But all hooked back up I can't blow on it myself BACK towards the tank.
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Unread 04-02-2012, 10:27 PM   #4
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I may just have to drop the d@mn tank again.
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Unread 04-02-2012, 10:31 PM   #5
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I wouldn't use your own lung power as a gauge. That's a pretty long run and small diameter tube to blow through... probably pop your ears! The only other question that pops into my head is... is the fuel pickup in the gas? Add another 5 gallons and see if you get fuel. Of course, it is then a PITA to drop the tank if you need to. I still don't understand why you collapsed the line when you applied vacuum? What kind of tubing are you using? How long is it? Is it collapsing when the pump tries to pull fuel?
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Unread 04-02-2012, 10:36 PM   #6
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kerrdogg-

I'm sitting here laughing because you are thinking along the same lines as me. I thought about dropping another 5 gal in it tonight, then I thought "Ah hell, then if I have to drop the tank it's going to be 42+/- lbs heavier!!

Good to know about blowing on that line (insert awful remark here). I did pop my ears. Red-Neck.

Its not fuel hose that I'm using with the hand pump. It's softer rubber (literally the pump is used to pull diff fluid/fuel). But maybe pulling the fuel through the sock, then the small line is just too much for the tubing?
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Unread 04-02-2012, 10:38 PM   #7
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The more I think about it... you mentioned clear rubber tubing? I would change that to a bone-fide fuel line before I tried anything else. I'm not familiar with a fuel-rated clear tubing. Maybe there is one, but I haven't seen it before. MY experience with clear rubber tubing and solvents is that it loses its rigidity in a short time. Collapsing would be expected in this case. Get some of the black fuel line and try that. I'll bet that's the problem.
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Unread 04-02-2012, 10:38 PM   #8
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Meant to tell you the hose I'm using with the pump is about 2 feet long. Maybe tomorrow I run a fuel like to an external tank, up to the mechanical pump, and see if that works? At least I can narrow it down as to whether it's an issue at the tank.
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Unread 04-02-2012, 10:40 PM   #9
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Quote:
Originally Posted by Skerr View Post
The more I think about it... you mentioned clear rubber tubing? I would change that to a bone-fide fuel line before I tried anything else. I'm not familiar with a fuel-rated clear tubing. Maybe there is one, but I haven't seen it before. MY experience with clear rubber tubing and solvents is that it loses its rigidity in a short time. Collapsing would be expected in this case. Get some of the black fuel line and try that. I'll bet that's the problem.
Agreed. I bet that is the issue. I'll let you know what i find out! Thanks!
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Unread 04-02-2012, 10:40 PM   #10
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I'm typing while you're typing!! So you DO have standard fuel line, and the clear rubber is just on the hand pump?
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Unread 04-02-2012, 10:41 PM   #11
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Ha! Yes, here is what I have:
Hand Pump>Clear Rubber "thinner" line>normal fuel line back to the tank>tank
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Unread 04-02-2012, 10:43 PM   #12
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Also meant to add that the clear rubber hose is connected to the hard fuel line. The hard line runs all the way back, except for a rubber fuel line section right at the sending unit. I completely disconnected the hard line earlier and hit it with some high psi air, and its most certainly clear now.
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Unread 04-02-2012, 10:49 PM   #13
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Figured I should stop typing while you're typing!! So... is the hard line factory? Any reason you should assume that it would clog? I like your idea of an external tank. That will give a good starting point pretty quickly.
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Unread 04-02-2012, 10:53 PM   #14
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I'm "assuming" the hard line is factory. I just bought this Jeep from my neighbor and am rebuilding it (on a budget-not a full frame off). The tub was swapped about 7 years ago and the original tank was leaking, so I replaced it a couple of weekends ago. Not much motor run time on the tank, but ran like a charm until today. Poured fuel in the bowl and it purrs again. It's all buttoned back up, so I'll try to crank it in the a.m. If it primes/works, then I apparently blew something out of that hard line. If not, I'll run the temporary tank.

Thanks for the help.
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Unread 04-02-2012, 11:00 PM   #15
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Good luck. Keep us posted...
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