Bike has 20,000 miles on it. It’s a 2006 that I bought 3 months ago so I don’t know the complete history. Anyway the paint on the tank looked great until today. It’s peeling around the tank filler. Also, inside the filler cap I can see black paint peeling/bubbling. I’ve never had a bike do this I did notice the bike drips gas out of the overflow if I fill it too much. A small puddle ends up in the garage floor after sitting the night after a fill up. Wondering if this is the reason it’s bubbling just under the filler cap. Anyway, it’s not something I want to deal with during the riding season. I just wanna stop it from getting worse. What would you do? Thought about touchuo paintvthen maybe a vinyl wrap in the short term...

Mike

Look at the small round ring near the 12 o'clock position. There's a rubber seal that can sometimes sit there. Other times it sits on the nipple end; shown hiding behind the gas cap. Follow the close at both points. There is your possible leak at those two points. However on the overflow slosh of it, that full tank is sloshing out the topped off gas out of those two points, well one actually.
The tank drawing shows a dotted line running inside the tank and out to the circled A behind the tank. That's the weather drain/bike washing drain hole for the recess for the gas cap design. That's the gas you are seeing coming out of hose part Circled-A 'drain hose.'

https://www.cheapcycleparts.com/oemparts/a/kaw/500b4e1bf8700223e4796048/fuel-tank

Missing Rubber:
92093-1030

Say pepboys or NAPA auto stores have touchup paint? Say car dealers may have touchup paint. Say fukdatchit and go match some nail polish at some beauty supply store.

Gotcha. Good call Hub. No seal on either the hole or nipple.
I’ll order one. Thanks.

Mike

DAMN!!! I have heard of this before. Not often but I remember a couple people had this happen.

I guess I would remove the tank, clean the flakes off and repaint it by hand. I'd let it sit indoors without gas in the tank for a winter and when reinstalled, don't fill it high for the rest of the year. AS long as the gas expansion can't travel over the filler neck, you won't get any liquid gasoline up there. You will still get fumes. I think putting the gasket in will protect fresh paint very well though.

Good call, Hub.

I guess I don't really know how the gas tank cap works. I added a picture with some questions. Today I stuck a piece of fuel line on the nipple shown to see if it was blocked. It passed air one way easy, but was harder the other way, like a check valve but not fully airtight in one direction. I can't remember now which way was what. I think it vented out from the tank easy but was hard to draw air in, although it was possible. Wish I paid better attention...
Also, how does fuel spill over the filler neck when the gas cap has a gasket that seals against the neck? Now that I think about it, how does the tank vent at all? Is it through the tiny hole in the center of the cap? As I look at it, it would seem that that nipple only vents from the overfill area/water drainage area up into the cap.

Finally, should I be able to blow air up from the overflow tube that hangs near the left footpeg?

Mike

There are tank designs with 1, 2 and 3 steel lines out the back of the tank... as you can see your design. Lines:
1. Vapor capture/overfill line enters the separator. The liquid is past thru the separator side for liquid.
2. Neutralizer line. This enters the separator as well. It filters the vapor to atmosphere and/or to a cylinder to fire off that vapor. There is a 14.7 psi that has to remain above the liquid [in the tank] so there is no vacuum occurring; where the tank can implode from the pressure change. So here is the air line more or less, while the first one is a liquid line.
3. The recess in the tank's gas cap mount needs a weather hole line. Look at the 3 mounting table stands under the gas cap. Follow the allen bolts. 2 bolts are fake so as to enhance the beauty ring or keep it more uniform. Those are your 3 triangle points for removal. Those legs are the reason for the sunken filler hole.... the flush mounting idea. Look for the weather/wash hole in the recess. Make sense it rains and if you pop the cap there goes the water in the tank?

The Gas Cap Design:
Where the two phillips screws are in the cap.
Where the ends of the holding plate have opposite protrusions in that rectangle block.
Those are for the springs and plate placements.
The nipple holds the closed plate side and closes the [air] nipple hole path to the flat washer or plate.
The tank side holds the plate or the ceiling washer, meaning, both look the same but are positioned oppositely.
The gas is sucked out of the tank via fuel pump.
The vacuum occurs. A soft spring holding the plate closed is now collapsing.
The vacuum lifts the nipple's side of plate open.
The ceiling plate has gas sloshing over the plate and collapses the spring letting gas in that cap's air gateway.
The gas is sitting there in the cap. The neutral pressure is about to change to vacuum pressure.
The nipple plate opens by vacuum. The gas in the cap runs out of that hole. For every action, that cap is clean of gas this slosh around, until the next vacuum pull round and keeps emptying the backwash of the high fill. Yes, they thought of the oops, I topped it off too much.

Make sense the cap is a pressure regulator in the static sense of its working movements?

* Last updated by: Hub on 8/22/2018 @ 12:20 PM *

My pre-anal, i only know it's there so here is my paint fix
I remove the 3 allens and now have access to the rippled paint.
I tape over, rubber plug the tank's filler hole.
I brake clean the rippled paint, let the gas/oily surface become clean via evap.
I pour clear nail polish over the rippled paint.
I brush it into the cracks so it binds to the ripples.
I move the bike out into the sun and let the clear cure.
I chose the closest nail polish color matching tank.
I brush that color on and leave a few thin coats.
I clear over it.
I install the cap.
I look back at my work and say, see it's not that bad after all.

Where a purist would say, fukit, it has character and patina I can live with.

Why doesn't this seal prevent gas from splashing over the filler neck.

See the tiny hole in the bottom of your gas cap? I'm guessing that is where the vapors go when they get pushed out from pressure. Same thing with gasoline when it gets hot and expands, goes right up that little hole there in the bottom of your cap. From there, through the cap and out the overflow vent nozzle that should have a rubber gasket on it. Then it goes through an empty steel tube inside the fuel tank (I know this sounds weird but look at the service manual for the diagram) to the back of the tank where the rubber hose fits on the nipple. The rubber hose routs to the LH side down by the clutch slave where you have seen the gasoline get expelled.

Is this vent supposed to be a one way valve?

IDK but what you recall observing makes perfect sense. Gas can flow out readily. Inflow is restricted to help keep crap out. The only reason for inflow is vacuum in the tank and that normally is a very slow process caused by the fuel level going down. Or contraction from cooling which also usually very slow.

Here's a diagram I made for my bus gas cap. Same general principal with most other motorcycle gas caps.

Ahhhhhh, ok, starting to make more sense. Thanks Hub and Rook.

Just got home from work and wanted to take a peak in the tank. I opened up the cap and gas exploded out like a fountain for a second. Geez. To date it hasn’t done that ever. There was no puddle on the garage floor. It did get warmer in the garage so apparently it’s not venting at all to deal with it. Also since gas was puddled all around the filler neck the paint is almost completely stripped from the inside of the tank recess. Fortunately it didn’t ooze out and eat the paint outside the tank. Currently siphoning the tank to empty it...

Mike

That bike has very low miles. It may not have expelled the wax packing they put in the breather tubes to prevent condensation during storage. I would not be too concerned about some pressure building in the tank. It will probably whistle after you shut down on a hot day, too. Perhaps it has not done that because none of the vapors have been getting expelled through the vent tube. They probably have all been getting vented into that round recess in the tank and they just escape around the edge of the fuel tank ring.

Pulled the tank today. Following your, Rook, how-to article I was surprised to see only one line at the rear of the tank. It’s the weather drain line. The only other line is the fuel supply line at the fuel pump. Odd compared to what I see others have. Anyway that line is clear after the tank. Blowing into it empties liquid out the line by the left footpeg. The tube coming out of the tank looks partially clogged. Working on it now.

Mike

I think the design is to capture the vapor from escaping into the atmosphere. Add heat; add very little air gap to expand; add how everything seems to say sealed. If say you top off the bike with a shot-glass of air between the gas cap and liquid, that is a perfect and fast, mind you, a vapor lock so fast, how fast is it? Before you get down to the block.

I opened up the cap and gas exploded out like a fountain for a second.

IMO, the only way to address the flaking/peeling issue is a strip and repaint. As for your vocanic gas gushing my guess would be that something is clogged or kinked.

It worked out great. I built up the paint chip with nail polish, sanding to level it. Then I cut a ring of black vinyl to cover it. Matched the paint nicely. Tank vent was the culprit. Almost completely blocked.

Mike