The carb generally used on the 2.4 engines is a Walbro WT76A, calibrated for the Sachs 3.2 chainsaw..There are 3 small holes in the venturi, uncovered one at a time by the opening of the throttle..The mixture to all 3 holes is controlled by the low speed needle. The three small holes could be the right diameter for a 2.4 engine if the engine manufacturer wanted to spend some money for a custom carb..As it is, they find one that works and use it stock...A prop with more pitch and/or diameter might load the engine at midrange enough to make the mixture leaner and get rid of the burble....Anything will be a compromise....