Berlin

Your description is definitely pointing to pilots. The small secondary jets in the float bowl and the small venturi running to them. They control the engine running at idle. If its running and taking off when you open the throttle you are then coming off the pilots and onto the needle and main jet.

There should be standard cab settings online and if I remember my RD350 settings the mixture screw was 2.5 turns out from closed. As a rule of thumb the bike should start and run with the screws out half of their setting range and then back in half a turn.

C