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Admittedly, my 96 KDX 200 doesn't get ridden as much as it should (but I plan on riding it more, very soon!), and so it just sits in the garage. I know these stock gas tanks may crack over time, and I'd like to preserve the tank from such a fate.

So, I'm thinking about buying and installing a Clarke Natural tank and storing the stock purple gas tank in my basement. Has anyone done this—and, if so, did the stock tank, when properly stored, maintain its structural integrity over time? Thanks!

Properly stored actually means keeping it topped off with ethanol-free fuel, and perhaps fuel stabilizer, and not allowing any airspace in the tank. Keeping it absolutely topped off is always best, especially if there is ethanol content in the fuel, as ethanol will combine with moisture in the air and drop out of suspension, leaving a corrosive gel substance to foul up the fuel system.
Also, if the plastic is allowed to dry out from being stored with no fuel in it, reintroducing fuel is much more likely to cause it to rapidly develop cracks overnight or in the next few days, and greet you with a garage floor covered in premix gasoline.
If you store an old tank dry for a long time, you need to very slowly reintroduce fuel into it. Start out with kerosene or diesel fuel and slosh it around inside, letting it sit and rotating the position it sits in from bottom to left side to right side to upside down etc until all sides have been coated and able to be rehydrated for lack of a better term, with the petroleum based fuels. After Diesel or Kerosene, I would do the same but mix some gasoline premix fuel at an 11:1 ratio, 1 gallon , and slosh it around the tank really good and let it sit for several days, rotating it everyday or every 12 hours to a different side of the tank. Obviously with the petcock on and in the off position and not allowing fuel to leak out the fuel cap vent.

Then after several days of this, add another 1 gallon of straight gasoline. Then after several more days or even taking a few weeks for each step of this process, eventually adding a third gallon of gasoline with no pre-mix, so you end up with 33:1 pre-mix, close enough for example's sake. 10.6:1 would be the actual 1 gallon mix ratio to arrive at 32:1 using this method.

You have to very slowly reintroduce petroleum based fuels products into the dried out used plastic, or else the old tanks will be more likely to rapidly crack from the chemical shock

I vote storing it with fuel in it will turn it brown. Look at the old tanks on eBay. If I had a dollar for every brown lime green tank I have seen from the early models. :-)

KDXGarage wrote: 01:34 pm Apr 27 2026 I vote storing it with fuel in it will turn it brown. Look at the old tanks on eBay. If I had a dollar for every brown lime green tank I have seen from the early models. :-)

Well that does make sense since all of the translucent aftermarket tanks always turn yellowish or light brown with the passing of time... The purple tanks, on the other hand, perhaps are impervious to that due to their coloration.
Yellowing or slight Browning as well as UV rays Sun bleaching and oxidizing the surface if it's stored outdoors or even in a garage with Windows in direct sunlight definitely will deteriorate the tanks.
My not so great quality spare purple tank was badly oxidized on the surface and faded purple, and with a razor blade and then very light careful use of a heat gun, scraping the oxidation off using it as a dragger blade perpendicular to the surface type of technique, restored it back to the exact original purple in the areas that I've rehabilitated so far just to check and see how solid the base plastic was on the exposed portions. It was more of a light purple at first (only after light scraping) than the proper violet purple when I only took off the initial oxidation layer, but the portions that are always covered by the shrouds and frame and seat are still looking like the original Kawasaki Violet Purple. So I would say it's fair to assume the purple tanks are impervious to that due to their darker color.

There was a clerk oversize 94-98 KX tank currently on eBay that is Sun faded and more browned in the tank portion versus the shrouds. This is the style where the tank wraps over top of the perimeter frame and flows into the strouds, but not quite fuel carrying shrouds as there is still a bolt-on portion of the shrouds. It looked pretty bad, to where I wouldn't even spend $95 on it, the list price if I recall correctly.

I think the worst I have seen is the YZ tanks from 1986-ish.

My original (turned spare) purple tank looks like crap. I hope the replacement holds up.

I just think the gasoline leaches through the plastic eventually.

I gave away my OEM green '99 KDX220 tank as my friend's '99 200H tank on a low hours bike had cracking radially out from the base of the fuel filler cap threaded portion from the 90 degree corner and our into the tank 2"-3", on a low-hours nice condition bike (the previous owner woods raced YZ250's, but had this as a leisure bike, hence it was in excellent condition otherwise). I attributed these several cracks from having some old fuel in the tank, but not full to the brim, and stored long term in that manner.
On older vintage bikes, the cracking of the dry storage fuel tanks within 1-3 days of reintroducing gasoline to them is a pretty common coincidence, and I am going to assume that this odd cracking pattern on this '99 200H tank was the same.

So if all of the above from all sides is true, you're darned if you do, darned if you don't...

Now I'm curious as to whether it's the actual gasoline that causes the browning of the tanks with age, or perhaps it has to do with the premix oil in the fuel? I don't have the time or spare tank to experiment with, but I wonder if one were to disconnect the fuel hose from the carb and plug it off with a note to self stating the contents, after draining the tank, and then filling it with ethanol-free 100% gasoline, no premix oil, if the tank would yellow or brown less or none at all?

The shortcut solution to an answer would be to look to Honda XR plastic tanks or other old 4-strokes, to see if they suffer this fate.

Good discussion.
Even though there is gas in it now (1/4 to 1/2), I think I'm just going to fill the current tank to the top.
Chuck, thanks for the advice -- much appreciated.

I'm totally clueless here, as I have no experience with what you guys are saying, but would filling it to the brim with Diesel work? I know it tends to be quite a bit less corrosive than gasoline is, so maybe it would be better to store it long term with it?
Plus no worries if you forget that's what is in it... it won't start with diesel, so no worries about accidentally starting it with no premix.

Just my thoughts, though they may be totally off.