When I had my idle about 1/8 turn too lean, it would do the same thing; I had suspected that the taxi out shook the fuel line just enough to add a bubble or two that would stop the barely too-lean engine. But I agree with the others, use an OS F plug. That is probably the real problem.

Clark

PS As a side, what prop are you using? Here in Austin (800' ASL) we all use a 16x4W APC on the Funtana 90.