Thanks for the information Dinkster. I still don't know why you have to bore out the small hole in the spacer. Obviously, the spacer port has to be enlaged to at least the size of the carb opening, or I guess one could just buy a big bore spacer. I have been reading that the Walbro 257 is the standard for this type of use, however, it seems many people are modifying this type of carb, although I don't know why as it seems they work just fine stock.