You can put a small clear tube on the bowl drain and hold it up along side of the carb then open the drain and the level in the tube is the level in the bowl. Should be about even with the top of the bowl with the bike standing up straight.
The o rings only need to be replaced if damaged on the pilot screws, had mine out several times over the years and never replaced, just a very light smear of grease when putting them back in.
Problem I found with HD dealers is the jets are too big, they run a single carb on a larger engine. Better off with a Honda dealer or other jap makes, they used the same carbs as us on certain models too.
