Anybody recommend a fuel additive or water-dispersing, or a fuel magnet, 4 stroke motorcycle?

AE86?

"Best" way I can think of (but it will ruin the tank of petrol) is to use isopropyl alcohol in it's highest concentration available. It wont make things "better", but it will attache itself to the moisture inside of the tank, so when you drain the tank the water will come out mixed with the alcohol rather than float on top and remain in the tank if you attempt to drain it.

If you're looking for a simple pour and clean solution, if you can find some methanol around, that works wonders too but it usually manages to burn off afterwards.

ethanol will work too if you can get the dry stuff that has had the water removed. they sell it in pharmacies overseas, inexpensive too.

terpene free ethanol overseas.

used for perfumes and extracts.

I drained the tank completely, ran the engine till it stopped

The inside of the tank is coated with flaky gunk, the bike is 20 years old, probably never been cleaned, can anyone in Phnom Penh clean the tank thoroughly?

If you have a metal tank and can manage to get it off by yourself, fill it with a bunch of gravel and shake it around. It effectively sandblasts the inside of your tank. Will make some neighbors angry most likely with the noise, but whichever...

Now THAT is useful!

On my to-do list for next weekend.

I think the neighbours won't mind (eventually), as my bike sounds like a 2 stroke on crack at the moment

any caveats?

This turned out to be a scam by the mechanic who knew he had used paper gaskets for my exhaust manifold.

Money-making strategy: on seeing the bike for the first time, predict worst scenario

Then use cheap, shitty materials to make sure he keeps coming back

Fucking chav cunt