I have a 92 sp 580. I have an issue where the motor is struggling to get to full speed.it gets to about 20 mph and sounds like the rpms are only about 1/2 throttle. Occasionally there will be a burst for less than a seccond where it sounds like the rpms shoot up then fall back to about 1/2 throttle. Also they will slowly fall until I'm doing closer to 10-15 mph. I checked compression and it's at about 130 psi on both cylinders i also rebuilt the carb over the weekend and I'm still having the same problem. Any help would be appreciated.