JoeW, I don't recommend teeny paper filters like you were describing. I use filters that are at least as big as the line on my bikes.
I run a 60cc Polini kit, and a 70cc kit, and have NEVER had a restriction or clog in any paper pleated filter that I've used in-line. But I won't buy little tiny ones.
Matter of fact, I believe I've only changed filters once in probably 30,000 miles of riding. My Banjo filter on the carb always looks spotless as a result of this in-line filter, and I have always been able to detect any water or dirt that got thru from the tank.
If dirt gets thru that banjo filter and stacks up on a main jet, you're possibly looking at a melted piston from running too lean. Not me,Bro!
I agree, though, that the filter must not be small. Toro has a good clear paper filter that's perfect for mopeds, and the ones I bought were from an Auto Value here in Jackson, and they had 1/4" graduated to 5/16" connections,to fit both sizes of lines. NEVER have had a leak either. No heat is even close to a filter on a Sebring,mounted under the tank.
NOW A TOMOS Targa and maybe others,has very little room for any filter, but I'd work around it. My 2 cents.