On 03/08/2011 19:23, Tim Lamb wrote:
In message , Pete
Shew writes
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).
Probably not the same as you have a magneto and, I assume, no battery,
but I had a similar problem with my B&S powered lawn tractor. I traced
the problem to the solenoid at the bottom of the carb. The purpose is
to retract a needle from the main jet to permit the petrol to enter
and to shut it off once the ignition is turned off to prevent
'afterfire'.

I replaced the solenoid with the appropriate UNF(?) bolt cut down to
length and, provided I slow the engine to idle before stopping, I have
no more problems with it.

Do you also have a manual shut off valve?

My Jonsered (different engine) has the same feature and, once or twice a
season, would fill the cylinders with neat petrol.

regards



No, no manual fuel tap, just the solenoid which stops the fuel leaving
the float chamber via the main jet. It was probably developed as a nasty
fix for when users turn off the engine at full throttle and are startled
by the bangs from the exhaust.

For some reason mine got weak when warm and couldn't pull the needle
down against the spring so shutting off the fuel. The solenoid seems
difficult to disassemble without damage and as a new one is close to
£100! it seems that a 10p set screw was the correct fix.

Pete