I assume the word "bot' is a typo meant to be "boat"
If idle adjustment screws existed on that 90hp model, they would be obvious at some location on the carburetors... BUT... those type adjustments are simply for idle and the lower speeds only. They have nothing to do with intermediate or high speed.
Bogging down and stalling when throttle is applied is normally contributed to a sticking timer base under the flywheel (retarded spark), throttle butterflies opening too soon in relation to the timing (*out of sync), or fouled, clogged, gummed, carburetors. It's usually the carbs but check everything I mention..
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*Synchronization: loosen screw and back roller away from cam.... make sure that the linkages between carburetors are such that "all" of them are fully closed.... make sure that the butterflies open and close at the same time.
Now, back to the screw at the roller... Adjust the roller so that the throttle butterflies just start to open when the scribe mark of dead center with the roller. The screw should be tightened at that point. You do not want the butterflies to open before or after that dead center mark happening.
That's the extent of Sync & Link.
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