98 250 Yamaha outboard. slowly lose speed/ RPM, and then slowly regain rpm and speed

1998 250 Yamaha outboard.
what would make the motor slowly lose speed/ RPM, and then slowly regain rpm and speed ?
[FONT=arial, sans-serif]and for some reason hitting the trim switch up or down, seems to make the motor regain rpm. I have replaced the trim switch made no difference, completely went through the motor tightened all ground wires, the motor is not dropping any cylinders it's just simply losing rpm, it never stalls or completely loses speed, it will go from about 4900rpm. and drop down as low as 3300 [/FONT]will run there for a few minutes and then slowly start to come up again, "if you leave it alone". If I give it gas it will take off but not at full strength. But if I hit my trim switch and "hold it", the motor will run correctly most of the time. the rpm symptom seems intermittent and random.[FONT=arial, sans-serif] I have also gone through the full system !
so it seems to be electrical, I just can't figure out what... thanks for any help !

David[/FONT]

David,
I had very similar issues with my '99 250,it turned out to be the stator. One motor went out on me and got it fixed, just 2-weeks later went out fishing and the same thing on the other motor. I first thought is was fuel starvation and changed all filters and rebuilt carbs. No change. As to your RPM gaining /dropping with your trim switch, normal for it to increase when you trim motors up (less drag on props).

thank you for your input, I greatly appreciate it ! I do understand trimming the motor up will increase the RPM. But [FONT=arial, sans-serif]hitting "(and holding)" the trim switch "(up or down)", seems to make the motor regain rpm ! ? I do believe that it is some kind of electrical issue !
[/FONT]"The stator" is not something I have considered. That is an odd component to cause such a symptom. can you please explain how the the stator would cause that problem ?
And thank you again. David