I had the same problem after fitting an aftermarket filter,after many hours I found it was because the new rubber sealing ring was thicker than the old one,I put the old one on and it was fine,you are drawing air in if it is not seated tightly,when you clamp it up push hard from the bottom and make sure it feels rock solid if it feels spongy it wont work,put the old seal ring on and try that,there may also be a lead below and infront of the filter to the pump which is a fuel cut off switch if so make sure it is connected.Also the fuel pipe from the tank behind the air filter may be joined by a short connector pipe that tends to split also causing air to get in,change the rubber seal back to the old one first though.
Rich, July 2007