High Vacuum in Gas Tank.

Gilleys 59 willys

Bigger Hammer
Jan 18, 2020
32
90605
First Name
Gil
Willys Model
Wagon
Willys Year:
1959
Hi all. I bought my Wagon not running. Steel tank was rusted through. I replaced the Stock Steel Fuel Tank with a Poly Tank. I also got a new Gas cap. I found the Fuel Pump to be Bad. I wanted to replace it , so I sealed the disconnected line at the Fuel Pump. After I replaced the Fuel Pump, I opened up the line and Fuel came shooting out like it was being pumped. I re-sealed the line and took off the Gas Cap. Massive suction. So then I connected the line to the Fuel Pump. Then I put the Cap back on tight. My wagon started right away, but Gas started to shoot out of the of the Carb. Went back to the Gas Cap and cracked it and got the same Vacuum sound. With the Gas cap loose, started it up again. Still shooting fuel out of the top of the Carb. So, to me , the Carb. is shot. But my question is : Is there supposed to be that much Vacuum in the system? Does the Fuel cap need to be a ventilated one? Thanks for any input.
 

Alan

Bigger Hammer
Mar 14, 2011
33
Nampa,Idaho
First Name
Alan
Willys Model
Wagon
Willys Year:
1953
You might not have a vented gas cap, and have excessive fuel pressure from your fuel pump. I'd check that first...good luck!
 

Gilleys 59 willys

Bigger Hammer
Jan 18, 2020
32
90605
First Name
Gil
Willys Model
Wagon
Willys Year:
1959
Alan , it's a Brand new Gas Cap that's supposed to be vented.. But your right,, it's gotta be the Cap. Ill look into replacing it. Thanks for your input.
 

Gilleys 59 willys

Bigger Hammer
Jan 18, 2020
32
90605
First Name
Gil
Willys Model
Wagon
Willys Year:
1959
Scoutpilot..It's a 59 Wagon 226-6 .Stock Dual Action Mechanical Fuel Pump. The Vacuum in the Fuel Tank is Incredible. (I guess it's a good thing that my Fuel System is tight)..I was asking to see if that was Normal or if anyone else has this Condition. With the Helpful Replies, I see it's the Gas Cap not venting. Thanks for your reply. In the Future I will try to be more Specific.
 

Mark W.

Sharpest Tool
Dec 6, 2014
389
Silverton Oregon
First Name
Mark
Willys Model
CJ
Willys Year:
1948
Vacuum in the tank would cause the fuel in the line to be sucked back into the tank if disconnected from the pump not spray out. If your tank is near full then simple gravity could be causing the fuel to spray out of the line. I have little experiance with these double pumps but could you have it hooked up wrong?
 

Gilleys 59 willys

Bigger Hammer
Jan 18, 2020
32
90605
First Name
Gil
Willys Model
Wagon
Willys Year:
1959
Mark W. .... I had a Theory that if you had Vacuum , the air you sucked in would be trying to get out. Like a Compressor. But now I see : With vacuum, you are pushing out air creating a situation where the air will be trying to get back in. With pressure , you are pushing Air in and it will be trying to get out. So , you are right! It's Pressure. I only have 2 gal. of Fuel in the Tank. It now makes sense. Since Air Expands and Compresses and Fuel doesn't. Having all that Air in the Fuel Tank Created Pressure. The New Poly tank is Black and it has been in the 90's out here. I opened the Gas Cap this morning, same thing , Pressure.....As far as the Fuel Pump hook up, Pretty much hard to screw it up. In the picture 1+ Inlet...2= Outlet. This is my first time dealing with a Dual Action Fuel Pump. I am now researching where the Ports lead to. I know one goes to the Intake Manifold. I don't know where the other side goes. But thanks for you help and Input! It set me straight.
 

Attachments

Gilleys 59 willys

Bigger Hammer
Jan 18, 2020
32
90605
First Name
Gil
Willys Model
Wagon
Willys Year:
1959
By the way, i know that Fuel line is too close to the Exhaust Pipe. I,m just trying to get this Baby Dialed in . I heard it run for about 10 sec,s before the Carb. started leaking .
 

Stakebed

Well Oiled
All-Star
Mar 4, 2020
2,155
Northern California
First Name
Joseph
Willys Model
Pickup
Willys Year:
1957
Number 3 goes to the intake manifold, number 4 has a hard line to the rear, past the manifolds, and then transitions to rubber for the wiper motor. I think the hard line bends up, vertical, before it changes to rubber.

On your gas tank/sending unit, is there any vent line? Not familiar with the stock tanks/SU's as mine were gone long ago.
 

Tinnocker

Bigger Hammer
Jan 17, 2017
148
Jasper, Ga
First Name
Robert
Willys Model
Pickup
Willys Year:
1963
I think you have two problems. maybe just one. When you opened up the gas line, gas came out, either by gravity or it was helped by excess pressure from the tank which would be from an unvented cap or tank. If the cap was vented or the tank was vented then the gas coming out was just gravity pulling it out of the tank. If it was just gravity then that would be normal.

Now the gas coming out of the top of the carb is another problem. The only way that the gas can get past the float valve is by a bad or leaking float or a piece of trash holding the needle valve open or the wrong pump producing so much pressure that it forced the needle valve open. The engine should have choked becoming flooded and quit running before it got to that point but I guess some gas could have come out of the carb before the engine died. Sometimes you can tap on the side of the float bowl and dislodge the trash but most time it needs to be taken apart and cleaned. Some pumps produce more pressure than others so I would check to see if I had the right pump first.
 

Gilleys 59 willys

Bigger Hammer
Jan 18, 2020
32
90605
First Name
Gil
Willys Model
Wagon
Willys Year:
1959
Stakebed...I've seen through pix posted that indeed #3 goes to the Manifold. Thanks. I just dont understand why the intake for the wiper vacuum would have to come from the intake Manifold and the Fuel Pump. #3 on the Fuel Pump does read "Inlet".
 

Gilleys 59 willys

Bigger Hammer
Jan 18, 2020
32
90605
First Name
Gil
Willys Model
Wagon
Willys Year:
1959
Tinnocker...The Carb is shot. I'm getting it rebuilt.. I got the Gas Cap and Fuel Pump from Kaiser Jeep. The Fuel Flow is fine. I guess the Cap is Vented for Vacuum (For Fuel Flow) and not for Pressure. I'm getting pressure from the near empty tank and the hot Summer Weather here in So.Cal. Thanks for your reply.
 

Scoutpilot

Sharpest Tool
Nov 1, 2014
343
Asheboro, NC
First Name
Rick
Willys Model
CJ
Willys Year:
1948
Before the introduction of the dual-action (fuel/vacuum) pump, drivers complained, and rightly so, that when they were using the windshield wipers during acceleration of the motor the wipers would slow or stop. This happens because when acceleration occurs, the intake manifold vacuum decreases. The vacuum side of the pump picked up the slack somewhat. Then someone came up with the idea of electric wipers. The vacuum pump was also used to augment the PCV vacuum.

Yes. The fuel tank cap should be vented to allow fuel to flow, via gravity, to the pump.
 
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