Should be 30 amp slo-blow fuses. There are two coils in the starter solenoid. Initially, both are in use when first starting as a much higher current
is required to engage the pinion gear
. Before the solenoid is fully engaged, it could easily draw 25-35 amps. After the solenoid is fully engaged one of the coils is shorted out and only the holding coil is in use which requires only around 10 amps to keep the solenoid engaged. This is the reason many setups, including modern Yanmar
systems, use a slave solenoid mounted on the engine
. Much less current
is required to operate the slave solenoid so you don't have this high initial current through your start switch.