My SF-400 of ´94-95 is running nice from 1000- 5900 rpm. At 6000rpm sharp there is a big hesitation to increase revs, especially if with the heavier gears (3-4 etc). If I get to 6200 it then goes up very fast. If I have hi revs with 1 or 2 gear and continue high,no problem. What can I do?