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Pressure build up in fuel tank - Normal??

br2an

Active Member
Joined
Dec 31, 2013
Messages
28
Location
NL, Canada
2001 JCB series 3 backhoe that has a fuel leak. I know where the leak is and what is causing the leak but I'm not sure what the real problem is.

Here goes: when sun hits the fuel tank in the morning, tank warms up and pressurizes the tank. (think of a plastic fuel can that swells up when left in the sun) This pressure build up causes fuel to leak out from the top of the fuel sediment bowl. (not sure if a fitting or seal or ??) If I loosen the fuel cap overnight, no leak the next day.

Before I pull the fuel sediment bowl apart and fix the leak, should the fuel system be building up pressure? Or should there be some kind of a vent in place to relieve the pressure. If I remove the cap after a couple of hours of just sitting in the sun there is a very noticeable blast of air/fumes.
 

Tinkerer

Senior Member
Joined
May 21, 2009
Messages
9,342
Location
The shore of the illinois river USA
The cap must not be venting properly.
Yes plugged vent.
Not only that ,but when you run the machine awhile a terrific vacuum is created in the fuel supply circuit. Most likely that is why the sediment bowl gasket is leaking. Determine how it is vented and repair it properly. I have seen faulty fuel cap vents that dumped fuel on the ground after the tank was filled and the air temperature went up.
 

thepumpguysc

Senior Member
Joined
Mar 18, 2010
Messages
7,445
Location
Sunny South Carolina
Occupation
Master Inj.Pump rebuilder
Vents can be cleared.. I'v also seen people take a file or grinder to the threads, longways to cut a groove..
normally when someone buys the wrong cap.. non-vented.
 

br2an

Active Member
Joined
Dec 31, 2013
Messages
28
Location
NL, Canada
I had a chance to take a closer look at the cap yesterday, should have taken a picture but I found these on the internet that should work. There appears to be a small screw and two rivets holding the clasp to the underside of the cap. I can see two small holes (vent holes??) but no appearance of an external vent. Does anyone here have any experience or can shed some light on how JCB vents their fuel tanks? Don't want to attack the cap (which probably means I will have to purchase a new one) if the vent isn't in the cap.

Edit: Considering just removing the seal for now, that way I can at least lock the cap and keep anyone from tampering with it.

cap2.jpg cap1.jpg
 

br2an

Active Member
Joined
Dec 31, 2013
Messages
28
Location
NL, Canada
Finally had a chance to bring the hoe down out of the woods for some servicing and had a good look at everything.

I could blow through the fuel vent with compressed air but could not get WD40 to spray through from the can. Is it possible the cap has a pressure release valve built into it, something like a radiator cap but maybe lower pressure?

Checked where the fuel was leaking from the sediment bowl and had a loose fitting. Re-tightened and everything seems fine so far. I burned 1/2 tank of fuel today and no problems so I know the vacuum side of the vent is working as it should.
On a side note, was not able to prime the fuel system using the manual lever on the fuel pump. Those things are not very user friendly.
 

melben

Senior Member
Joined
Jan 14, 2008
Messages
1,026
Location
Williamsport, Pa
Occupation
Retired 50 Yrs with Case dealership
Usually the engine has to be turned so the cam lobe is away from the fuel pump lever before the manual lever will work, if it dont work, turn the engine a turn and see if the lever on the pump firms up.
 

br2an

Active Member
Joined
Dec 31, 2013
Messages
28
Location
NL, Canada
Usually the engine has to be turned so the cam lobe is away from the fuel pump lever before the manual lever will work, if it dont work, turn the engine a turn and see if the lever on the pump firms up.
Yes, I did read that in another post. Tried just touching the starter key a couple of times but no luck. I ended up pressurizing the fuel tank with compressed air and forcing fuel up into the system that way. The fuel pump is obviously working, would you recommend I remove it for inspection to see why the manual lift is inoperable? Or is it most likely my inexperience.
 

Delmer

Senior Member
Joined
Jan 3, 2013
Messages
8,863
Location
WI
Don't remove the pump, disconnect the output and/or inlet to see what's going on. They're simple pumps, I assume this is a lever that operates a diaphragm. The lever and cam pull the diaphragm back against the spring, and the spring pumps the fuel out under the correct pressure, the pressure builds up and holds the diaphragm away from the cam/lever, so you won't feel any resistance once it's pumped up. Alternately, if it's sucking a vacuum it will be harder to move the lever, vacuum plus the spring pressure.
 
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