I found that BAL needles were OK on my B20 (with milled and ported B20F head
and IPD 7001 cam) either with or without filters. K&N are
somewhere in between. Needles are about the last thing you change unless
you have some that are REALLY unsuitable (like for a MUCH bigger or smaller
engine than yours). BTW I am also using HIF6 carbs on a B30 with the same BAL
needles and the big flat air cleaner and they work great there too. Seems to
do about the same with the aircleaner removed.

I'd suggest that you make sure you don't have air leaks and that your mixture
is adjusted right. If the seals on your throttle shafts are old you should
replace them to eliminate a pair of potential air leaks at the worst possible
place on each carb.

Also make sure your float level setting is right and that your float valves
are indeed opening and closing like they are supposed to do.
--
George Downs, Bartlesville, Oklahoma, Central US