The KB2A carb is an excellent upgrade carb for 30ci & 40ci and the 44ci motors like MK58A.  They are a fixed jet, you can jet them to your application.  Carb is clean inside but will need a service kit, gaskets & needle/seat.  This carb has a .055 jet.  They also work out nice on 2 cylinder motors.  I have one on a KG7 Pumper A block.