More information required – what model Villiers engine? I presume that you are referring to ignition timing and not valve timing ? Some engines have their flywheels keyed to the crank so the basic timing is set by design. Others have the flywheel secured on its taper with no key and it has to be positioned in relation to the piston position – slightly more complicated.
So, what have you got, images are always useful.

Check the outside perimeter of the flywheel for an arrow stamped into the rim . This arrow was put there on assebly when the factory had timed the engine to make it easier to retime in the future.
First check and adjust the contact breaker points to between 12 and 15 thou.This has to be done with the flywheel in place as the points operating cam is integral with it. Its a bit of a fiddle as it has to be done through the “window in the flywheel. I usually start with a clean 12 thou feeler gauge and settle for a slightly loose sliding fit but having tighten up the adjuster clamping screw just make sure that a 15 thou feeler will not go through the gap. That way its probability 13/14 thou. Having done that pull a clean piece of copy paper through the closed points to remove any traces of dirt. When pulling the paper through, stop before the end so that the points don’t snap down on to the edge and pull out fibres which cause a problem later. Hold the moving point clear of the paper.
The next step is to remove the cylinder head and turn the crank to top dead centre with both valves shut. Then while making sure that the crank does not move turn the flywheel so that the arrow lines up with the small protrusion cast into the magneto back plate.
Tighten the flywheel – very tight – Villiers sold a special spanner designed to be struck with a hammer.
If you have not got a flywheel with an arrow the job is a little more complicated. Set the points gap as above. Then find top dead centre with the valves closed and rotate the crank anti clockwise to lower the piston 3/16″ down the bore. Then ensuring that the crank does not move turn the flywheel so that the points just start to open. The traditional way to determine the “just” was to place a strip of cigarette rolling paper between the points and apply a little tension. “just” is as soon as the points release the paper. Then tighten the flywheel.
Gets easier with practice!