One thing not asked in all this is how much service has this mower
seen?

It was a gift for my (since passed) mom in May 2006, a Lawn Boy 10686. I
liked the intuitive propulsion (just pushing the spring-loaded handle makes
it go, no other control) and the electric starter. She mowed the small
front yard by herself into her mid-80's. It's a small fractional acre
suburban lot so 11 years of that.

The negatives on this unit: The key starter switch fell apart twice, once
under waranty. I eventually replaced it with a pushbutton on a box
(containing a relay since the button could not handle the current). And
the Molex or similar charger connection with a 12V cigarette lighter type
connector.

And though the manual mentions an high lift blade I don't think they were
ever made so we were left stuck with a compromise blade. The last mower
(which I still have) I removed the original compromise blade and got a
lift-only. Far superior if you bag and want to use the mower to suck up
leaves & debris. The compromise blade lifts at the sides but blows down in
the middle for mulching purposes. I should look into an aftermarket blade.

You can tell the compromise blade because if you approach debris on the
driveway it is as apt to blow it away as it is to pull it in. The
traditional blade was more like a vaccum cleaner.

This morning I pulled out the mower and followed official procedure with
the primer bulb. No start. I shot in a few cc's of gas and pulled the
cord and it started and ran. It doesn't sound totally right but it was
running just from a hand start. This whole thing is puzzling.