70cc aerox won’t run with air filter

Hi, trying to get my sons aerox running right!
Has a sports pipe, put a stage 6 70cc kit on it, started and ran ok, but was REALLY slow off the mark, so put a 17.5mm carb on it from Pedparts, put it all back together and long story short it ran like a bag of poo!
Take the air box off though and run an open carb and it runs and rides great.
Even putting a piece of the mrs’ tights over the carb inlet makes it ran bad again!?
Any thoughts? I’m competent on 4 strokes but not done much on two strokes.
Jetting in new carb is 95 main.
My thinking is it running really rich, and by putting the air filter on it’s making it worse to the point of not revving cleanly, tried leaning it of on the needle position but no difference.
Would going down on the main jet help? anyone had similar problems?
Cheers lee

 

That's because the air/fuel ratio is wrong.
Grab a box of main jets and start working DOWN in size, one at a time, until you hit the right one with the air filter ON.
You'll probably end up somewhere around the early to mid 80's.