If the stock carb and stock air box was 90 Main Jet and you added a unifilter on it, you must increase the Main Jet size. In other words, go to a higher number. The reason is, the unifilter will let much "more air" into the carb and thus, you need "more gas" to keep proper balance of air/gas mixture. If you go with a untifilter, I've read that its jetting might be between 110 - 130 Main jet(depending one's altitude and weather temps).
If wondering, we had a 82 Main jet in our '03 Pred-90 16mm carb with its factory air box and its long skinny snorkel "straw pipe". I kept its factory air box and replaced its skinny snorkel with a shorter, wider inner diameter snorkel pipe. And this new pipe has a smooth 90 degree bend instead of the factory sharp 90 degree bend. For a picture, surf: http://community.webshots.com/photo/...29655958iCaQAK
To set our 16mm factory carb to obtain "light black / dark brown" spark plug color, I had to install a larger size main jet. The jet size for its customization and my specific altitude is 87.5 (hot summer) and 90 (for warm winter). Thus proving that I had to install a larger size main jet.
If your upgraded air filter allows "more air" into the carb, then increase its main jet size (NOT 90 down to 75). This will lean the carb's mixture and in a short period of time, it will burn a hole in the piston (from running too hot).
Unfortunately, I can't guess the 3 jet sizes you may want to play with. For my custom config, another person guessed 87.5 and 90. With their many years of experience, they were right on. For your unifilter, I'm not experienced enough to guess. But I do know it's probably in the 110-130 range. Hopefully, another person on this forum will make an educated guess on what 3 jet sizes (above 90) you may want to start with....
Note: Check its spark plug color NOW. If it's white or has white spots, do NOT run it anymore. White means its running too hot and within 4 minutes of running above 1/4 throttle, it will blow your new engine upgrades apart. Instant piston melt down as well. That I do know for sure....