Oh boy, so will check again after work. 900 is in the river i assume? My water bucket’s water was warm because it sat outside all day. Not sure if that makes a difference?
I don't think water temp should really matter. Definitely set the idle with motor in the water. Needs the back pressure to be correct. A bucket should be ok, just not off a hose with muffs. Honda says 900 +/- 50 for your rpm's, so even closer to 1000 rpm's should be okay.
That adjustment if for the air/fuel mixture, idle rpm is the other vertical screw if happens to be so. Must turn it CCW till rpm begins to drop to factory rpm parameters. If without a tach, simply turn idle screw CCW a bit to a point than when gearing forward a smooth gear sound is heard and engine doesn't stall, if does, turn screw CW a bit till that cond is met.
Adjust idle rpm with engine sufficiently warmed up and on water, not on bucket as idle rpm will vary once engine sits on water.