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Discussion Starter #1
If it's a warm day or the sun is beating down on my fuel tank, it builds up pressure and is constantly venting through the valve near the front on the top of the tank. This goes on anytime the ambient temp is over about 70 F. When I'm at the track I have to shade the tank and constantly open it to vent the pressure because liquid fuel will begin to come out of the vent. It even built up so much pressure once that it filled all the carbs and fuel began running out of the bowl vents.

Is this normal or an indication of something?
 

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It is normal for fuel to expand as the temp rises. If you are at the track don't top it completely until right before you go out that way you will use the extra fuel and leave room for the rest to expand. When you fill up at gas station leave about a 1/2 in of air space below the filler neck. I have the problem every once and a while with fuel comming out of the carb overflow vents...THIS IS CAUSED BY TWO THINGS. 1. one of the floats is stuck open. or 2. If your running a Pingle petcockit can allow so much fuel that it overwelms the floats and than fuel comes out of the vents.
Bones
 

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Discussion Starter #3
Thanks Bones...I'm not sure what a Pingle petcock is. Are you talking about the stock one that is vaccum controlled? If so will changing it out to a manual one stop the overflow problem?

So I'm also guessing from your reply that the vent valve is working normally, so replacing it won't help.
 

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Pingles are manual. Do you have a hose on your vent tube? Maybe one of your floats just had a speck of rust in it.
 

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Discussion Starter #5
Originally posted by 88/750:
Do you have a hose on your vent tube? Maybe one of your floats just had a speck of rust in it.
<font size="2" face="Verdana, Arial">Thanks 88/750...No hose on the metal tube that sticks out from the bottom of the tank. I thought that was just for water that gets in around the filler cap...right? There is a hose coming off of the vent valve and it's routed into the headstock.

I was just down in the garage and the tank still sounds like it's venting even though it's been cool and out of the sun all day. I know fuel expands as the temp rises...but the temp has been stable and or decreased...so why does it always make that sound?
 

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My partner's FJ 1200 does that a lot... *especially* after riding and the tank is getting low... I think it's just pressure equalizing in the tank... expand, contract, whatever the fuel does, air has gotta get in or out to compensate. I wouldn't worry so much about the noise, I had a GPz that used to do that all the time... but if you want to stop the fuel from coming out the vent tube, here's what you want:

http://www.airtech-streamlining.com/miscairtech/fuel.html

open up that site, and scroll down and check out the "Fuel Tank Vent Line Check Valve".
 

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Discussion Starter #7
Thanks FastCat...Guess I'll just ignore it since it isn't affecting performance. I'll keep the check valve in mind but I haven't actually had any fuel come out of the vent yet. It's only a problem when it gets a pressure build up and ends up coming out of the carbs.

Thanks to everybody for their input
 
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