On 2008-05-16 10:13:24 +0100, Yuri said:

teapot wrote:
I have a Sovereign Classic 35 lawnmower with a Briggs and Stratton

FWIW I have just had a mower fuel problem that turned out to be caused
by 'old' petrol. according to the mower repair shop modern unleaded
petrol goes off after approx 12 weeks. Mine had been serviced in the
autumn and came to use it two weeks ago filled it up with last years
petrol - no water or contaminants - and would start but not run.
Apparently this is a common fault and some engines like my Honda are
more prone to this than others.

Yup. With my Mountfield petrol mower, every spring I would need to
empty out any remaining fuel and replace with fresh, then also take the
spark plug out and bake it in the oven for a while. If I didn't do
this, there was no way in the world it would start, but with this
procedure, it always started on the first pull.