We're in India at the moment, having travelled thru Turkey, Iran and Pakistan.
We have 2 BMW F650's, the non Fuel Injected model.
The fuel is a bit dirty and can have water in it, even when it comes from a proper gas station. (Some fuel you get is from drums on the side of the road)
We first noticed it when we filled up some spare containers, and saw all the crap floating in the bottom.
The particles are very small. They look like dust particles. I don't know how you would go about trying to filter it out... Maybe the coffee filter you suggested would do the trick.
We haven't bothered about filtering it because we can drain the carb's and empty the fuel tank's easily if necessary. Having said that, we haven't needed to do that yet (touch wood).
The fuel tap's on our bike's have filter's, and we fitted in-line filter's as well.
A friend of ours went from UK to Singapore last year on a 650 Dakar and had no problems with fuel. He didn't filter it either.
Hope this helps...
Good luck with your trip.
Trent and Jacqui