Or, some minor blockage in line or filter. Might even be debris in main
fuel jet.

Suggest you note current main-jet adjustment (how many turns in to
gently bottom it), then remove it with mower outdoors. Clean what you
can- your might have to pull the seat part of the jet. Fuel should
trickle out the jet; do what it takes until it does (with fuel in tank,
of course.)

Put main-jet needle back as it was originally adjusted, and do the std
stuff to adjust it.

HTH,
J

Check the vent in the gas cap....

I had the same problem with a Toro Selfpropelled I bought used this
spring. The lawnmower would run for a couple of seconds after being
primed an then would die. I knew there had to be some debris somewhere
so this is what I did.

1) Drained the gas tank and put some new gas in with a little carb
cleaner
2) Primed the lawn mower
3) Started the mower. Keeping one hand on the kill engine leaver I
would reach over and press the priming ball if it felt like the mower
was about to die. I was able to keep the lawn mower going like this for
15 minutes and eventually the debris passed through.

I don't know if this will work for you but it did for me.

Cheers