Check the needle and seat in the carb. Mine once came partially unscrewed and jammed against the float. (Rochester BC one bbl, hot air choke) This prevented much gas from getting into the carb, so at highway speeds the carb went dry and the engine died.
Get a new heat riser spring, make sure the spacer is under the carb, and go through the carb for loose parts, plugged passages or bad gaskets.
good luck
chip
