Yamaha 40 2 stroke gradually loses power

Hello
I have a 1998 40 Yamaha two stroke that runs like a top with good
compression, but does have one issue.

It runs fine on wot but sometimes after a few minutes it gradually
starts slowing does just as if you very gradually were letting off the
throttle.

As soon as you let right off the throttle it seems like it "catches or resets"
and powers right back up. It never misses at all during this process.

I asked a mechanic a few years ago and he thought it an electrical part
which might have been the CDI (although I am not totally sure what that does) and that was going to be $700, so I never pursued it.

I had the Yamaha mechanic check it over this spring before selling
it and he said the problem was just a fuel oring on the fuel line that
was sucking air and he tested it, but we run the boat in the water
and it was doing the same thing. I am going to try with a new fuel line
and bulb as that would the only variable that might be different. I think
he also put in a new fuel pump, but not sure.
Thanks for any help.
Graham

Re: Yamaha 40 2 stroke gradually loses power

Do you know what RPM you are running at WOT that this problem shows up? do you think it is hitting the rev limiter?
I have a 1999 C40 that does about the same thing, feels like dropping a cylinder, but if I run it without the silencer on the front of the carbs it does not act up.
I still have not got my hands on a tach that works properly on these CDI motors to check my max RPMs to see if it is over reving. I tried a ESI 321 digital Tach but it will not work with these motors it just goes crazy.