older evenrude 35 having troubles

last summer I bought a 15ft alumna craft with an older evenrude 35 on it , the first couple of times I took the boat out with no problems but then it started to kinda like jump anytime I went above idle speed so I didn’t think it was a big deal . but I took it out the other day and now if I go any faster than idle speed the motor slips in and out of forward gear very severely but when this happens the rmps stay up. the motor will stay in reverse just fine but slips out of forward gear …
any suggestions would be great thanks

Could be the linkage is off some & needs to be adjusted. That happened with one of mine but it would jump right back in gear as fast as it jumped out of gear. I had no issue in Reverse either.

It doesn’t take much for the shift linkage to get out of adjustment. I messed mine up when I put a new water pump in a few weeks ago. Got it back right now. Depending on what year it is, some of the old Evinrudes used a plastic compression type collar to lock the shift linkage together, that thing will get smashed or worn out and cause forward issues.

218WA Sailfish
200 Verado
The "Penn"sion Plan

Had same issue with my older 25hp. Only did it few times to start with, but as time went on it would pop out of gear every time I would take off. I replaced clutch dog and it fixed my problem… Hope this helps

225 SeaHunt
F200 Yamaha