98 50hp 2 stroke went to half power

[Craigslistmaniac]

Was cruising 4800 rpms on plane (throttle all the way down), smooth water no wake, all the sudden engine slowed down to 2400 rpms (throttle all the way down still). Thats as high as it will go. Idles fine revs fines and purs like a kitten, just no top end at all. Any suggestions of what happened? No alarms went off

 

[99yam40]

Test to make sure the alarm works
Check to see if timing is retarding when this happens