See page 95 in the owner's manual
http://marine.honda.com/pdf/manuals/00X31ZY06310.pdf. It shows you how to drain the carburator. The screw is in the carburator (do not loosen it all the way to take it out...just loosen it some). The hose is attached to a nipple on the carburator float bowl and runs out to a nipple on the side of the engine that is next to where you see the water peeing when the motor is running.
It is hard to tell if you have the right prop. You want lowest speed at idle and fastest at full throttle.....You can not have both. It is a compromise. It also depends on how many people and how much stuff are in the boat.
The prop you have is 1 pitch less than the standard prop that normally comes with that motor. You can go all the way down to a 6 pitch, which would probably be good for your trolling but suck at top end...in fact the motor would probably hit the rev limiter.
Hondadude: Thanks for the very valuable information, etc. I am going to try the motor either this weekend or next as it is still a little cool here in UpState NY. Is there any way I can use a Tach on this motor to accomplish my objectives ? And if so, where can I come by one as inexpensively as possible ? I have been doing a little research on props since I have been on the forum and I am wondering what a 6 pitch X 9 1/4" FOUR blade one will do but I guess at this point in time the best way is experimentaion or Tach method if I am able to do it that way ?
I would try what you have and see how it does. If it seems to bogg down when you are trying to accelerate, then you might try an 8 or even a 7 pitch if it is really bad and you have a heavy load.
As for changing thermostats etc. Do not modify what thermostat that it has. Make sure you are using 10w30 motor oil. type FC-W (not synthetic oil). Also, be sure that your oil level is no higher than 1/4 inches below the full level.
Be sure to always use NGK brand of plugs that were recommended for the motor....no substitutes.
We sell a lot of these 20's to Barge companies on the River to use on each tow boat. Likewise, we sell many to commercial outfits that do water cleanup (lots of idling as well as a need to go fast). They are used is some very hostile environments. Other than getting the cooling system clogged with "whatever they were in"....ash pits, spills, etc, they keep on ticking.
As you can see, I am kind of biased.
Mike