Typically on two cycle non fuel injected engines the carb cam will open the butterflies about 1/4 of their maximum at about 3/4 throttle on the control handle. At this point, timing is almost 100% advanced. What this does is to give better fuel economy at cruise. Note the difference is that at WOT on a recreational engine and boat the engine makes a lot more noise, uses a lot more fuel, but only drives the boat a couple of MPH faster. In fact, if you look closely, the linkage will slightly retard timing a degree or two at WOT. This is to help prevent piston damage.
Because of the nature of the carb, the high speed jet LIMITS the amount of fuel delivered at WOT. The reason is that as more air flows through a venturi it will get progressively richer until at WOT (if there were no high speed jet) it would be too rich for correct running. Thus, at about 1/4 opening the venturi is starting to deliver fuel and while it is less than at WOT, it is not very much less because it is close to the limit set by the high speed jet. So, you save a little fuel at cruise, but not as much as you would hope to save.
Most outboard carbs are dirt simple. They do have a low speed circuit BUT since the low speed circuit is always at manifold vacuum it aleays delivers fuel. The high speed jet is sized to account for this fuel. That is why if you set the low speed needle too lean the engine will melt pistons at or near WOT
