high idle when slowing down

You might try readjusting your throttle cable as follows:

1. Disconnect cable from carburetor.
2. Place throttle control in forward detent position. I.e. tranny in gear, but at idle speed.
3. Adjust end of cable so that when connected to carburetor the throttle plates remain closed.

Most people do not do step #2 and thus can have problems. Not saying this will fix it, but is where I would start.

You might want to check to make sure the high idle cam, if present, is not sticking. Check for binding of the throttle cable.

is it a FI or carb motor?

Awesome advise guys. I will go look at that later tonight. I am hoping to get it out this weekend but my honey-do list is pretty long. I have messed with the linkage and it did get funny going into forward and reverse. Funny as in it would engage but too much fuel was being delivered. Once engaged, i was able to pull back on the throttle and make it run right. Reverse got a little silly that way too. So it looks like I need to do this procedure and get it set per the instructions.

AWESOME!!

I would say that it needs adjusted at the throttle as well as at the carb. The cable should not move forward at the carb when engaging a gear. Now if you are going past the detent when shifting from neutral thats a little different and I would call that driver error rather than bad adjustment.

Well, when on vacation I decided to make these adjustments. I moved the ball socket on the carb linkage because the throttle plates were staying open. then I decided to lower the bracket because it has always bound somewhat. Got it on a level field finally. Adjusted the ball socket for the proper length (or so I thought) so it would slide right on the carb. Everything seemed to be better because I was now getting the full speed out of the boat and it was much smoother throughout the throttle travel of the lever. BUT that is when I started getting these engaging problems. So that is the full story. It has always engaged forward and reverse properly...like new...but the throttle plates were forced open a bit. That is why I did this.

I looked at that on vacation and it looks pretty complex. I am not around the boat, but is that something that screws can be taken out from the "outside" and pull the mechanism out to work on or is it something you have to "press and guess" your forehead against the wall to figure out. Sorry for the stupid question, but it sounds like I have tinkered too much and may have gotten myself into too much trouble already.

What is this brass thing you are talking about and what would this adjustment really do? Sorry, I always have questions and want to improve my boat.