Dave & Propworn,
Thank you for all your input. I promised get get back this Monday after going to the field to work things out. In my previous post I said that I had checked all the usual things, to no avail. I've been running O.S. 4-stokes for years with no problem at all. I would always build the plane, install the tank correctly, set the needles correctly, and fly happily ever after. Well as I said earlier, I had replaced some crappy ARF tanks that were suspect with my usual Sullivans. Going from an oversized ARF tank to the proper sized Sullivan trough things off. By simply returning the needles to the "factory suggestions" and starting over corrected everything.
Sometimes facing a new situation in engines requires us to begin again at the basics. Setting the main needle slightly leaner and adjusting the idle one correct for the new main setting did it.
Thanks to all that helped.
Karl