As MotorGeek said go with a richer main jet. I'd say a richer pilot too. No lid means its running lean. Typically you don't want to leave stock jets in with the air lid off. Damage may/can/will happen.

One thing that worries me about changing the needle clip on my LT500 is the fact that they do not make the top gasket any longer (At least the OEM shows not shipping) so it would worry me to mess around with the clip on my 500 anyway.

Clip up = leaner Clip down = richer