'73 Evinrude Sportster 25hp - Slipping out of gear?

[scorpionic]

Hey all, just found this site and I'm hoping I can get some nudges in the right direction with my outboard issue. The 'board in question is my 25 hp '73 Evinrude Sportster. It's my first ever outboard purchase (high-five!), bought mid-summer last year, and it has already given me hundreds of hours of floating and fishing serenity. Overall, it's really run great since I've owned it. However, just recently it has started doing this weird thing where I'll be cruising at any constant speed, from low to wide-open, and the engine seems to slip out of gear and rev up. It also seems like the prop disengages when this happens, so I feel like it has to be slipping out of gear. It's to the point where I can sense it coming, I think because the hum of the engine is slightly different when it's having "one of those days". This does not happen every day, and oddly, it may do this funky stuff and then be completely fine the next day, or even later that same day. (Short video with sound displaying the problem can be sent separately if interested).
Do any of you guys/gals have the know-how to give me a good starting point to try to remedy this? I'm admittedly a novice when it comes to anything that drinks gasoline, but I'm willing to put in the time and effort if I was nudged in the right direction. Thanks in advance to any that read this.

 

[Daviet]

Re: '73 Evinrude Sportster 25hp - Slipping out of gear?

Engine speeds up - boat slows down.
Sounds like you have a spun prop hub. Remove the prop and make a mark from the hub to the outer housing of the prop, run it until it does it again and then check to see if the marks are still in alignment, if the marks have moved you need to have your prop rehubed.

 

[scorpionic]

Re: '73 Evinrude Sportster 25hp - Slipping out of gear?

Thanks for the tip, I'll definitely be checking that out as soon as I can get it back jn the water. I'll post my findings.