Classic/Antique Car Repair: engine diesels, gasoline engine, dieseling

Question
Just changed the points ,rotor and cap , a 77 MG engine continues to run after shutdown

Answer
you did not mention if this was the reason you did the changes.

Dieseling or afterrun in a gasoline engine is excess gas in the exhaust chamber. It can be caused by severely advanced timing or improper fuel ration or flooding.

Occasionally in older engines, it can happen when the idle speed is way too high.