I have a model 61 chainsaw that sat for a few years. I cleaned it up, flushed gas, new plug. Saw started, but barely. It ran like it was loading up. No change with any carb adjustments, just chugs. I put a kit on the carb, and it ran like new for about 10 minutes....then back to chuggin.....Any Ideas???? Carb adjustments made no difference again.