MG Car Repair: timing, lean mixture, combustion chamber

Question
My 1954 TF 1500 continues to run for a few seconds after switch is turned off.  I know this as dieseling, which I believe indicates a timing problem. If it is a timing problem I would like to know which way to turn distributor to solve ? Or do you suspect another issue.  Thanks

Answer
Hi Jerry,
The 1500 TF MG timing is set at TDC and points are .015" and rotor rotation is counter clockwise.

This needs to be set accurately and then set the idle. Even though timing can cause "Run On", there are many things that can also be the cause.

Wrong heat range spark plugs (heat range too Hot)
Excess carbon build up in the combustion chamber.
Over heating
Over lean mixture
Sharp edge of a head gasket in combustion chamber
Idle set too high
Float level set too high
Wiring or charging system problem causing power to enter the ignition   system from the generator after the ignition switch is turned off.
On other cars with higher compression ratio the grade of fuel can be a major cause of "running on" but this engine is not normally have a high compression ratio to require premium fuel but if the ratio was raised by resurfacing the head or block then it could be high enough to require premium fuel.

Howard