[We've had this discussion before btw.]

My old B&S-powered mower never starts. Not, that is, unless I spray a
couple of bursts of "Sure Start" into the carb. Then it starts first
time, and always starts after that, once it's hot. (Another regular
mentioned that spraying gas from a blow torch (i.e. not lit, obviously!)
into the carb works just as well. It's a bit of a fiddle taking the
air filter off then screwing it back on before pulling the cord -- but I
know it works, so that's what I do.

I never have the time, nor the inclination, to take it apart and try and
diagnose the problem further: my aim is to cut grass, and this is the
quickest route to that goal.

If the mower were newer I might be more concerned to get the problem
fixed.

Mowers seem to be an assembly of hard-rock components that will take
piles of punishment .... combined with little itsy-bitsy delicate things
like springs that have to be *just so*: nightmare.

John