Took it out Saturday. Cranks up fine. Idle fine. Above 2000 rpm it runs fine but between 1500 and 2000 rpm it will hicup every min. or so. When it does it. It will drop a couple hundred rpm then come back up. I have put new fuel lines and bulb. New pick up in the tank. It has clean gas in it. Any ideas what might be causing this? Thanks.