My mower is running badly?

My Mountfield petrol lawn mower is running really badly.

The engine seems to be surging then almost dying.

It is very difficult to start. There's a lots of black smoke coming out of the exhaust too.

I've taken the plug out and it's covered in black "soot".

It was fine last year but after putting in petrol and topping up the oil this year the problems began.

The mower is just over a year old.

It's a hand pull start 42cm mower LS45 with a Briggs and Stratton petrol engine

Barry Rinaldi
June 2004