HOW DO I SET THE TIMING UP ON A 125 PUSHROD ENGINE?

The timing on a pushrod engine is like all 4T motors, the relationship of the cam rotation to that of the crankshaft.
A common pushrod engine like a CG125 will have a mark such as a dot stamped on the gears connecting crank and cam which should line up at top dead centre on the compresion/power stroke,that is to say piston at the upper limit of its travel with both exhaust and intake valves fully shut.
Top dead centre is often marked in a similar way if you look on the flywheel for a dot or line and a corresponding mark in an inspection window or on the engine case.

Taggleflange
January 2009