What kind of bulb are you using to trigger the startomatic system? It needs to be at least a 40 watt incandescent light bulb, modern led bulbs wont work it.
This describes how to keep the set running without having to keep your finger on the button.
SECTION 5
PUSH BUTTON STARTING. HAND STARTING AND STOPPING
OF THE ENGINE
In the event of trouble developing on the switchgear or control
solenoids the engine can readily be started by hand and the plant
run direct on to the load by following the instructions given below.
Before resorting to Hand Starting always check:-
(a) That the trouble is not due to a blown fuse in the house
distribution fuse box or main switch-fuse. or perhaps
even a faulty lamp.
(b} That the battery fuse which is accommodated in the control
box on top of the alternator has not blown.
(c} That the Emergency Hand Reset Thermal Switch J has not
tripped. Press button with thumb to reset.
Move Rotary Control Switch IS to HAND OR PUSH BUTTON START.
FOR PUSH BUTTON START.
(a) Press the button labelled “Push Button Start”.
(b)} Operate the fuel control solenoid bell crank lever by hand
and insert the collar provided between it and the top of
the coil case.
FOR HAND START.
(a} Use starting handle as described in the engine instruction book.
(b} Operate the fuel control solenoid bell crank lever by hand
and insert the collar provided between it and the top of
the coil case.
TO STOP THE ENGINE.
Remove the collar from between the bell crank lever and the top
of the coil case.
This is a picture of a control box I rebuilt 5 years for someone else its still working fine.
Mick