Runs great at slow speed but when l try to go fatser it seems to be fuel starved?

If your fuel was oil mix in the tank did you drain it?? Fuel filter changed? Vent on tank pluged?
wrong prop?

No you do not need different fuel lines, but you do need to make sure they are in good shape and not dry-rotted or cracked. Yes, you still need the primer bulb.

Hopefully you cleaned out any mixed fuel from your tank (if you did not have an oil-injected 2-stroke). Running mix through your 4-stroke wo not necessarily hurt it, but it will smoke really bad and will probably foul the plugs pretty fast. which could cause it to run poorly.