What was the outside temperature when you noticed the power loss?
My Rincon seems to be doggy in the mid range and top end when the outside temperature gets below 40F to 45F. This has been the case even after a 5 minute warm up period before riding. This slowly improves after a few minutes of riding to get the engine up to proper temperature, but there still seems to be some power loss when riding below this temperature range.
Since you are in Washington it must be cold there as well. I suspect our carb settings need to be altered for cold weather riding, but I am not exactly sure what needs to be changed.
Something that was brought to my attention is the fact that I am using 10W-30 Motor oil in my machine. This on top of the fact that its cold outside makes the bike run slower in the top end. I am going to change my oil as soon as it gets warmer to the honda GN4 oil just to see if this makes a difference. I know the oil is used for the engine AND the transmition. The Tranny I belive is being bogged down by thick oil...
rotella synthetic 5w-40 from wal-mart 12.88 gallon,works great in low temps(teens)with wind chills colder.aprox 800-900 miles using this oil with no problems so far,i also use it in silverado 1500,and my street bike and when spring hits i will switch both my honda aquatrax's over to it too..