I had some problems with engine noise at higher RPM's, so I retarded the spark, and now it runs so much better and quieter. I tried retarding it more and retarding it less, and found what seemed to be the sweet spot. Now it's comfortable at 50 mph.  I was curious, so I checked the timing with a light , and it was retarded 10 degrees at idle (400 rpm). So I put it back to 0 degrees at idle, as specified in the manual. Doing that gives me about 10 degrees advance at 1500 rpm. At 2000 rpm I ca