You need a battery and lamp to set the timing up correctly.
Find the wire that goes from the points to the coil and disconnect it.
Connect a lamp and battery as follows: battery negative to engine casing, battery positive to one lamp lead, other lamp lead to points wire.
You only need a small battery and lamp for this 1.5 to 3 volts if you have it.
What will now happen is the points will act as a switch and all the while they are closed the lamp will be on.
Now look on the outside of the flywheel and you will find two marks , one marked 'T' and the other 'F'.
Rotate the engine by hand in the normal direction of rotation and wait for the lamp to go out - the 'F'; should line up with a mark on the casing (sometimes the casing join}.
Adjust the points gap until the marker lines up i'e as 'F; passes marker - light goes off.
Be accurate.
When happy remove lamp and battery and reconnect points wire - start engine.