The only 2 things I've been able to do with those long foam filters that make it reasonably ridable without just constantly fouling sparkplugs are:
1. make the foam THIN in between those 2 steel perforations. The Henry Abe foam usually disintegrated pretty young. I once bought a foam filter for a car (round) and took it apart to get that thin foam (about 3/8" thick), then ran it without any oiling. It worked OK until hiway speeds (70+), when the turbulence started messing up the airflow in the carbs.
2. extend the bowl-vent tubing on the carbs (there are 2 on the roundtop carbs, 4 on the early cable-carbs) way back to a quiet area, like in between the battery and oil tank, and make a 3-hole container (like a pill bottle) that will accept the 2 vent hoses (or 4 if K0 roundtops) and have 1 more hole for them to breathe through. This will at least keep the bowls at somewhat higher pressure to push the fuel up the emulsifiers in the carbs. This will help to mitigate the plug-fouling troubles and will reduce the 'flat spot' often found around 75-90 MPH when running without a baffled airbox.
