What would cause my Honda 30 to drop in rpm when warmed up in neutral at idle from ~950 to ~625 rpm (where it becomes really rough) I give it some throttle (1200 rpm) then stabilizes back to ~950 rpm then slowly drops back down (2-3 minutes). Haven’t let it drop till the engine dies. Running at speed and when in gear at idle aren’t any problem. Only when in neutral at idle. Happens both on water and on muffs, seems more exaggerated with muffs. Autostart enrichment valve?? Any ideas would be greatly appreciated. Thanks.