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KTM Gas Tank Pressurized
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KTM Gas Tank Pressurized - July 9, 2013, 12:31 PM

I'm hoping REDLEVEL sees this thread, but feel free to chime in

Last week at Taskers my KTM 400 was blowing bubbles out the vent tube all day. I've never noticed much of this before, and didn't notice it this time until the tank was about half empty. Temps were in the 80's.
Is this "normal"?


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July 9, 2013, 12:34 PM

is there a check valve in the external vent tube?


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July 9, 2013, 12:37 PM

also, is the vent tube clear? As in, you can pop it off and blow through it?


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July 9, 2013, 12:43 PM

^ Agree. I would check the tank vents and make sure they're clear.


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July 9, 2013, 12:57 PM

knock out the check valve ball in the cap, or if you are running a stubby vent hose throw it away and get a normal one.


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July 9, 2013, 12:59 PM

Put yamaha sticker on the tank and all the problems with the tank will go away and it will work perfect! LOL
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July 9, 2013, 01:59 PM

Quote:
Originally Posted by Scot View Post
is there a check valve in the external vent tube?
No, I'm assuming there's a check valve in the stock gas cap.

Quote:
Originally Posted by Scot View Post
also, is the vent tube clear? As in, you can pop it off and blow through it?
It's clear tubing and I could see the bubbles merrily making their way to the headstock. Makes me believe the tube is not clogged.

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knock out the check valve ball in the cap, or if you are running a stubby vent hose throw it away and get a normal one.
Is that a pretty standard mod? I'll take a look at it tonight and see if doable without me destroying the cap.


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July 9, 2013, 02:11 PM

Quote:
Originally Posted by WKDBLD View Post


Is that a pretty standard mod? I'll take a look at it tonight and see if doable without me destroying the cap.
yes, std procedure on a RFS

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Fuel Tank Vent

This hose has a couple underrated functions, the one we commonly think of, as fuel is consumed, the level goes down and air must flow in to replace it. What we may forget is these four strokes have the engine and tank so closely integrated that the tank/gas get hot! This is OK but often the gas expands faster than the engine burns it so early into a ride it is not uncommon that if the tank can not vent out the gas becomes under pressure, this sinks the float, floods the engine and frustrates the rider to no end. Tank & cap must be vented to atmosphere both ways.
Dave’s way: Take your gas cap apart and toss the check ball. None in the hose! And while we are looking at that, take a look at where the hose goes. When that gas expands we do not want overflow dumping on the head pipe. KTM was clever in routing it into the frames down tube, that way it can drool out on the ground and bypass the hot exhaust.
Another good tip in this area, remove the tank and use self sticking aluminum foil under the tank to stop engine heat from penetrating the lower tank and heat the gas.


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July 9, 2013, 02:38 PM

Interesting, that seems like a pretty basic thing for the factory to get wrong.
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