I have used the SS filters like the one Nick shows and also the sintered bronze filters with good results. I wouldn't worry too much about the micron size. 150 microns is much smaller than any carb jets or galleries. Only in fuel injected engines does micron size become important. Despite the Rotax recommendation, I use paper filters in my 912S.
The Rotax recommendation is there for good reason. Never use paper filters with fiberglass fuel tanks, with older fuel lines that are not rated 30R7 or higher, or systems that have recently switched over to ethanol/mogas. Ethanol does not hurt paper filters. Millions of new cars are sold every year and they all have paper filters.
The problems usually arise when older systems have been recently switched to ethanol. The ethanol, which is a solvent, begins to loosen old deposits which will clog paper filters because they filter down in the 10-20 micron range.
I reiterate. THE ROTAX RECOMMENDATION IS WELL FOUNDED AND SHOULDN'T BE IGNORED. That being said, I prefer the paper filters because they are cheap, they are ethanol resistant, they filter much better than SS or bronze (10-20 microns), they have a huge filtering area in sq/in compared to the others, and they have a very low pressure drop across the media. All things being right with the rest of the fuel system, I have found that the paper filters are OK.
Bill.
