"Peter C" wrote in message
ps.com...
Mountfield petrol rotary mower with a Briggs Stratton engine.No
problem starting. When accelarating to cut the lawn it is mis firing
and black smoke emits from the exhaust.
New plug fitted. cleaned air filter.
Where do I go next please.to solve the problem?

Is it a two-stroke engine?

If so, the petrol needs to be mixed with the appropriate oil.

--
Brian
"Fight like the Devil, die like a gentleman."