ive got a yamaha jog r technigas exhaust do i change the main jet?

ive got a yamaha jog r (same engine as aerox if it helps lol) ive put a technigas next r and 4.2 gram rollers but it stuggles 2 do 45 shud do at least 50 i was just wondered do i need 2 change the main jet because ive got a sports exhaust onit??

my mate has a aerox same exhaust but lighter rollers 3.5 gram and his does 55 60