Only the track can decide the proper carburetion; the trolley can be used to pre-heat an engine, but even maximum acceleration does not provide the necessary information, because the engine doesn’t have any resistive load.
As a starting point, adjust the screws for low and high revs as directed by the carburettor manufacturer. Then, after a few revolutions to bring the engine to the correct temperature, begin the carburetion for low revs. Floor the accelerator out of the corners and if engine response is a bit hesitant (the engine revs take forever to speed up and there is a lot of smoke from the exhaust), it means that carburetion is “rich”, so it becomes necessary to slightly tighten the screw closest to the engine until the kart achieves a linear progression out of corners. However, if the revs do not increase instantly and the kart only accelerates sharply after a slight delay (the switch effect), accompanied by an almost metallic noise, when you floor the accelerator, then carburetion is lean and you have to loosen the screw to increase the flow rate of the mixture.
Once you have achieved a satisfactory setting at low revs, turn to the high revs. If at the end of the straight the engine (with the correct ratio) does not reach maximum revs, it means that thee mixture is rich and you need to tighten the screw closest to the filter so that the engine revs increase until you start braking or until the rev limit is reached.
To get an idea, you can use the air filter: if the kart accelerates when you plug one of the air inlets on a straight, it means that carburetion is lean; if it slows down, it is rich. For engines with rev limiters, please note that in order to achieve maximum revs, the intervention of the limiter automatically makes the carburetion richer, because the oil/fuel mixture does not ignite due to misfiring.