Get two toggle switches.
One should be on/off
Other should be momentary.
Three 16 ga wires, i would suggest 4 ft long each with alligator clips on one end of each wire.
Also use fork or ring terminals ends for switch connections. Dont just strip wires and wrap the around terminals....do it right!!
Red, yellow, purple wire colors.
connect short red wire to one terminal on each switch.
Also coonect long red wire to ONE of the same switch connection.
Connect purple to other terminal on On/Off switch.
Connect yellow to other terminal on Momentary switch.
On/Off switch in the OFF position.
Connect red to battery.
Connect yellow to slave solenoid small yellow with red, or starter solenoid same wire, small yellow with red stripe.
Connect Purple to coil +
With all wires connected, unplug if you want, the large wire harness connector.
(Make sure key is out of ignition switch)
Disconnect throttle cable from carb and you will work this by hand.
To use this rig correctly,
Turn on/off switch on. This applies power to coil.
Now activate Momentary switch. This will engage starter.
in your case, if engine starts, release Momentary.
If engine starts, to shut down, turn On/Off switch OFF.