The mower is about 25 years old and has been used throughout the grass growing season in all those years.
Presumably if the compression is low the engine will not start when cold, but is OK when hot because the piston rings have expanded?
Sort of. In reality you need a lot of things to be 'just right' for ignition - air/fuel ratio, compression, spark and spark timing. Being cold is one thing that makes all the others more marginal
make sure its got plenty of oil - that helps seal the rings.
However its usually valves on a Briggs, that go first - can be reground.
If it won't start, it may be difficult to get it hot enough for the rings to work!
I'd stick a new plug in and see; alternatively clean and gap the old one.
This is a good generic guide:
Thomas Prufer
Many thanks to all those who replied.
It was mild today so I tried the mower. Sounded completely dead when I tried to start it.
Removed the air cleaner and gave it a good spray of Holts Cold Start in the air inlet. No change.
So took the plug out and sprayed some directly into the cylinder. Replaced the plug and it started second pull with no choke. Ran fine for the hour or so it took to cut the grass.
A 400ml can will probably last me the rest of the winter!
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