Old fuel can cause varnish buildup on the intake valve stems, jamming them in the guides, leaving the stuck-open valve to be bent by a piston.
Used to work at an engine shop, saw it several times.
I would never run old gas through a motor. Ever.
Had a gasoline Ford tractor that the stuck open valve was bent and had to replace….major expense. Never try to operate with gas that has gone bad from sitting a long time….lesson learned.
