"The3rd Earl Of Derby" wrote in message
. uk...
Bob Mannix wrote:
"Carpii" wrote in message
oups.com...
Hi., I just bought a brand new petrol mower this weekend. I measured
and filled the oil and petrol correctly. Its a 4 stroke engine

It starts without too much difficulty (though not as easy as Id
expected).
After mowing for maybe 30 seconds, the motor rapidly fades and then
stops.
At this point the starting cord is very tough to pull, and I
generally have to leave it for a while before I can start it as
easily as before.

If the engine is getting tight as you describe it indicates it is
seizing due to lack of oil. How you square this with having filled
the oil correctly I don't know but, if it were a fuel problem as
others have suggested, the engine would not be tight. Without looking
at it it is difficult to help but I would siggest, at least, getting
a second opinion on the oil filling.

Nothing to do with pressure in the chamber then?
It being brand new an all. ;-)

He said "very tough to pull" so I would say not (as you ask ). The pressure
will release as soon as a valve opens, which will be after a small fraction
of a revolution, after which there will be no pressure - unitl - the main
pressure is built up during the compression stroke (obviously, the clue is
in the name) which will be the same whether it has just been running or has
been left for a while. A new mower will have higher compression than an old
one but it won't change from minute to minute.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)