Yamaha 25 2 stroke idle

I have a 2005 Yamaha 25 2 stroke. I put a brand new power head on it less than 6 months ago after the motor overheated due to corrosion build up in the water jets from previous owner not flushing. I broke in the new power head exactly how the procedure said. Motor has ran perfect with no issues. This weekend I was scalloping in homosassa and when I came in the last day I noticed the motor was idling very high. Between 1800-2000rpms. Motor usually idles at startup around 1100 and quickly settles in between 8-900rpm. I got home and hooked up the muffs to flush it and it was still idling high so I turned the idle down on the carbs and it seems normal now. My question is what would of caused it to idle up so high? The motor had a load the last day because of the 10+ mile run in rough weather and occasionally had to stop because I was sucking up grass and motor would temporarily stop peeing.(not long enough to do damage) . motor ran perfect despite idling high and I just want to make sure the cause isn't something that will cause damage in the future. Thanks