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Weird Gas Tank Issue

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Hey Guys!!!! First time posting but have been riding for a long time and have a weird issue with my KTM. I have 2000 KTM 250 SX. I have a 4.0 gallon I believe Clark gas tank(bought it a while ago and dont remember the brand). There is a very small gas leak and i cannot tell where it is coming from. I pulled the tank off resealed the petcock and thought that fixed the issue then i tokk it out rode for about 4-5 hours then loaded it back in the truck and noticed some gas in the petcock area. Also it leaks just while sitting. So last thi i have done is pulled the tank filled it with water and kept it in a more controlled enviornment to see if it was leaking and nothing. Any thought or help would be awesome if you need more info please let me know

 

Matt

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First, your test is invalid as water may not leak when gas will, so you probably will have to go to something else, like back to gas or alcohol or something, make sure it is all dry and then watch it - it will probably start to drip within a few minutes if it is going to leak.

 

The other option is to add some light pressure into the equation, like put a piece of hose on the gas gap and blow into it to help force the water or gas out the leaking area and see if you can find it.

Rob

 

Question:

Why is it that gasoline has larger molecules than water molecules, and yet gasoline can escape through holes that are too small to pass water?


 

Replies:

The reason for this is water has a very high surface tension (72ergs/cm^2) compared to hydrocarbons (~ 21 ergs/cm^2). Remember that the size of the "holes" you are referring to (say 0.001 to 0.1 mm) is much larger than the size of either water or hydrocarbon molecules, so the size of the molecules does not come into play. The ease with which a liquid will pass through a large hole is complicated, but an important factor is how well the liquid "wets" the walls of the hole. This "wetting" in turn is proportional the inverse of the surface tension (approximately). So the LOWER the surface tension the easier it is for the liquid to pass through the hole.
 

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Rob,

Thank you that was helpful but it turns out it wqas the petcock inside the actual seal and on/off/reserve section was dirty and I believe it was causing back pressure and forcing the leak. As of right now there are no leaks but now I have to much gas going into the carb which is an easy fix so that im not worried about. On another note I have a little bit more testing to do but i think my shifting rod on my 2005 Raptor 350 is bent because I cant get it into certain gears. It's stuck in third right now, but i could get it to shift from first-neutral-second then back down but once i shifted it to third i can't shift into any other gear and I verified it's not the clutch. I am going to put a direct shifter on and try it and see if it was just the wierd linkage that the raptors and the warriors use.

 

Matt

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Glad you figured that out - I had a warrior long ago, but can't remember enough about it to be helpful - it could be the rod is bent, especially if it will move but not move enough to change to another gear - good plan on ruling out the linkage first though - always go simple to complicated!

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Well Rob, Simple it was!!!!! the guy who had the Raptor before me lost the bolt for the front part of the linkage and didnt replace it with an oem bolt so luckily the front part of the linkage that connects to the shifter shaft. Half the teeth were worn down so it would not shift there.

 

Matt

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Well Rob, Simple it was!!!!! the guy who had the Raptor before me lost the bolt for the front part of the linkage and didnt replace it with an oem bolt so luckily the front part of the linkage that connects to the shifter shaft. Half the teeth were worn down so it would not shift there.

 

Matt

Always like the simple ones like that - beats opening the cases!!

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