'Mike' wrote:
Air filter VERY important. Clean that before you do anything else. The
machine demands air to run, blocked filter starves it of air. FULL STOP
ENGINE.

Spark plug almost as important. A wire brush will clean that and as a VERY
VERY rough guide, the gap between the electrodes should be the thickness of
a thumb nail.

I realised those - they were dirty but cleaning them was the first thing I
did when I started working on the mower I did toothbrush and meths
treatment on the plug - scraped away much of the carbon on it.

Though the clean and dry air filter sponge soaked up much more oil than I
expected... should I squeeze out as much oil as possible (to allow the
airflow) or is it better to keep some in (to collect bits of dust, I
assume)? I don't think it was originally very oily, but the previous owners
of the mower did zero maintenance on it so that's probably not a guide.
FWIW in testing (on concrete, not cutting anything, not dusty air) I ran it
with no air filter until I got it started.

Theo