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

I have a Mountfield LS45 that was working fine until I hit a stone. The engine now runs too fast and the mower vibrates. Can anyone assist?

Matt Davis, September 2012

my briggs and sratton ls45 carburetor is not mixing fuel correctly mixture is too rich. have checked choke mechanism all ok. Cleaned carbs all ok. Engine using far too much fuel - black smoke coming from exhaust as though engine choking itsel. Please can anyone help.

Graham, August 2012

I have just had the same problem it turned out to be the choke had stuck,the carb is bolted on and 2 bolts are hard to see at first, be carefull when taking apart as there are 2 plastic seals that join to the body you will see the choke ,put a touch of wd 40 move it with your finger ,should then be ok

john pettard, May 2007

your engine is running too rich (too much petrol). find the main jet on the carb and adjust it (normally you turn it clockwise a little at a time but be carefull not too tight or it will break!!). adjust it so the engine will carburate smoothly from idle to full throttle.
but before trying this, make sure that the choke is not still on!!

Jammin James, November 2004

Get a good Hayter

Dave Dale, July 2004

Yep - that's about it. Then runs like it's gonna give up at any minute...

Barry, June 2004

like the first 5 seconds it runs good then it starts missing black smoke and runs real bad ?

Stewart L. Hockenberry Sr,, June 2004