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gas tank pressure build up???

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hey guys-

I have a 09 530 Exc and have noticed the last few times i went riding that there seems to be pressure building up in the gas tank. I have the bike desmoged and have one of the after market one way valves on the end of the gas cap line. i have also taken out the ball that's inside the gas cap it's self. i haven't noticed the bike running weird or anything but after riding for a few hours and turning off the bike i can hear air (As well as see gas fumes)

being pushed out the one way valve. (strange sense it's a one way valve that's only meant to let air in i assume)

I have never noticed the bike doing this until recently and was wondering if it's something that may cause problems or if there's something i need to do to prevent this from happening.

Thanks in advance for the help

-Rex

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I wouldnt use a one way valve.

The venting may be cuz its a 4st and the pipe runs close to the tank and when you turn it off or sit for a minute the heat gets to the tank and gas causing it to expand. They make heat tiles for this, but I just turn my bike off it Im gonna be stopped for over a 30 sec or so.

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you guys think i should just ditch the the after market one way valve on the end of the gas cap line and run the gas cap line to the grey elbow on the frame thats near the head tube? That way air can flow in and out freely. like i said before i already have the ball taken out of the gas cap it's self so there would be nothing to stop fuel from running out of the gas cap line in the event of a lay down/tip over if i did this.

-Rex

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I wouldnt use a one way valve.

The venting may be cuz its a 4st and the pipe runs close to the tank and when you turn it off or sit for a minute the heat gets to the tank and gas causing it to expand. They make heat tiles for this, but I just turn my bike off it Im gonna be stopped for over a 30 sec or so.

Yeah im the same way i always shut her down if i know that i'm going to stop for more than a few seconds. didn't really think about the pipe being right there to heat up the tank/fuel causing it to expand when it's just sitting there after a ride. this could vary well be the cause since the heat is just rising right on to the tank. it's just that i have never had it do this until recently and nothing has been changed on the bike for months part wise. the bikes not getting hot enough to engage the cooling fan either.

-Rex

Edited by REX RENOLDS

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This is a very common problem with KTM's.

Do not run any after market check valve on the vent line and remove the check ball from the gas cap. The tank must vent freely in both directions.

Run the hose to the elbow on the steering head (stock location on 06 and down).

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so where dose the grey elbow that's on the frame near the head tube go? i'm just worried about where the fuel is going to end up in the event of a tip over since there's nothing stopping it with the gas cap check ball removed.

-Rex

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it keeps the gas off the motor and exhaust, safer than anywhere else. It runs down the frame tube and out the bottom.

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One way valves are just not good. Think about what happens when you stop and park your bike in the sun. Your fuel expands and has to go somewhere. A one way valve will force it into the carb flooding your bike or pushing it out the carb vent tube. Imagine it's in your garage all nice and cozy and your garage heats up to 100 degrees and the sun shines thru the window onto your bike and gas flows out the carb onto the floor.

Imagine your bike is in the sun outside and it's hot out and the tank is full , ever seen a gas can thats been all bloated from sitting in the sun.

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it keeps the gas off the motor and exhaust, safer than anywhere else. It runs down the frame tube and out the bottom.

Just took a piece of hose and hooked it up to the grey elbow near the head tube then spit some water thru the hose/elbow to see where it would exit the frame and it came out all over the header pipe (2009 frame) not to sure i like that. I think what i'm going to do is just drill a hole in the check cylinder that's in side the after market one way check valve (should be able to do it thru the hole in the nipple) and that should make it a two way vent letting air in and out freely.

can any one think of any reason this wouldn't work? any reason i shouldn't do this?

-Rex

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the check valves have been known to sometimes stick and build pressure up causing carb flooding issues, or a vacuum issue not letting gas IN the carb. Works both ways.

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Whats wrong with just hose and no drilled out check valve?

nothing at all just figured since i already have the check valve why not make it a two way vent. might keep the line from sucking some dust and will still look legit.

a drilled out check valve IS a hose....:banana:

Ha! pretty much. I didn't mean i was going to drill a hole straight thru the thing. just a hole thru the piece inside the check valve it's self that gives it it's one way valve function.

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just drilled out the inside piece of the check valve making it a a two way vent. like others have said it severs no real purpose except looks but figured what the hell.

-Rex

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Ok now it's time to go out and do some testing to be sure it works. Start with uphills followed by downhills, left turns followed by right turns, more up and down, more left and right, hot days cold days ETC....

Just go ride it.

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This is a very common problem with KTM's.

Do not run any after market check valve on the vent line and remove the check ball from the gas cap. The tank must vent freely in both directions.

Run the hose to the elbow on the steering head (stock location on 06 and down).

so do u just take the screws outta the gas cap to disassemble, remove the check ball and reassemble? :banana:

TIA

:lol:

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my 06 has the "quarter-turn cap" just remove the three screw and remove the ball...sucker is big... :lol:

...~5/16" diameter.

:banana:

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