On 31/07/2011 06:22, Gib Bogle wrote:
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired I'll
take them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).

One simple thing to check, could the petrol reservoir cap air vent be
blocked? If it becomes blocked, you will gradually get a vacuum in the
tank. An easy way to check would be to wait until it stops and loosen
the cap. If you hear air rushing in and the engine then starts, invest
in a new cap or make a small hole in the old one.

--
Howard Neil