1999 Johnson 150hp runs rough when put into gear and starting off

I have a 1999 Johnson 150hp on a Javelin Fish/Ski. Today, I was pulling my 5 year old son on the kneeboard at a slow speed like I've been doing all summer and everything was fine. We then rested for a while and went for a boat ride. Then as I started to pull him again, the engine ran very rough and shook a lot as I was pulling him. I pull him about 10 or 12mph. I had him get back into the boat and tested it a little and every time I put it in gear and gave it the throttle it woul run rough and shake as I was planing off. I could then take it on up to around 45 or 50mph and it ran like normal, but at the slower speeds it ran rough and sounded rough. What could this be? Why would this problem suddenly show up from one run to the next? Any thoughts on how to troubleshoot this or fix this. I have very limited mechanical skills other than I do know how to change spark plugs. Thanks.

Re: 1999 Johnson 150hp runs rough when put into gear and starting off

im thinking buy a Mercury!.. haha j/k im having a similar problem with my 1997 150hp....runs fine starting off then when im on the water for an hour starts to run like crap(especially at low rpms) and can barely keep running... problem has gotton worse since the spring. always did good at higher rpms. ive changed fuel lines and filters. new plugs brand new fuel pump and nothing has worked....my next step is the electronics...yours could be a carb issue

Re: 1999 Johnson 150hp runs rough when put into gear and starting off

Sounds like a hanging shift interrupt switch.
Down on the shift linkage stb side, black switch that slides up and down when shifting. Try to disconnect it. If that works, spray with WD 40 or similar so it moves freely when shifting.
NB: when disconnected, engine might be very hard shifting OUT of gear!!!

Re: 1999 Johnson 150hp runs rough when put into gear and starting off

Thanks for the replies.