Our 9yro petrol lawnmower (Briggs and Stratton series450 148cc model SV40S) has failed for the first time. Yesterday it started and then struggled to keep going, konked out. I restarted it, then it died again after a couple of mins. Today not starting at all. I have de-oiled the sponge air filter, and oil (albeit old!) level is fine, as is fuel.
Any ideas, what can I try?