My lawnmower suddenly lost power whilst mowing - it just about chuggs along but almost stalls.
It also belches smoke out of the exhaust. Sparkplug gets very sooty and the oil seems very runny and black - only changed about 3 mows ago.
As fuel tank empties the engine speed increases and gets back to normal just before it runs out of petrol.
Any ideas?

jamie, May 2010

Poor running caused by too rich a petrol/air mixture,so either too little air (filter blocked) or too much fuel (carburetter problem). Solution is to change filter and clean carburetter. Problem seems to solve itself as petrol runs out beacause the mixture is forced to be correct, then too lean, as last fuel is consumed. This final lean running (luckily) also burns and cleans spark plug.

jdN, May 2010