My Honda CD250U Right cylinder runs richer than left

[nofacemonster]

I recently bought a Honda CD250U Motorcycle, i loved it's styling etc. Everything is stock except the air cleaner wasn't there so i used a foam air cleaner instead of a paper based filter. cleaned the carburetors, did a 1 Turn per each carburetor on air / fuel screw. Now bike runs ok, but right cylinder runs rich. What could cause this? i can hear a little backfire on exhaust as well from right cylinder. Should i turn the air/fuel screw of the right carburetor to another half?. Or i should switch the air filter to a paper based original one instead foam?.