I have a 1979 Honda CX500 Custom. The bike is in good shape, about 25000 miles, starts right up, idles great, carries good compression(168 lbs in each cylinder). The problem is, about 4000 rpm, the engine cuts out. it will go right back to idle, but it will not run smoothly above 4000 rpm. We went through the carbs and cleaned them and no improvement. have any idea what the problem could be?