Smell the oil for the presence of gas. that would indicate fuel leaking through the needle/seat assembly.
However, if it's a fuel pump engine, it may only empty the fuel line. That relatively small amount could easily get missed.

IF the carb solenoid is leaking, you should be able to see it unless it's very slow.

A few things you can check/try.

Make sure the choke plate is fully closing on the carb.

After the mower has sat for the "usual" extended period of time, remove the carb bowl and see if it's empty. That would tell you if it's leaking out or not.

Try priming the carb first with 2-3 teaspoons of gas and see if it fires "right up".

The carb solenoid LEAKING is not a problem with starting. It also does not affect whether gas can leak thru the carb into the cylinder. It only affects gas flow thru the main jet.

The carb solenoid does have to open allowing gas to pass for the engine to start.

Priming the carb is a good idea.

Walt Conner

Ding, ding, ding. The winner is "choke not fully closed". Had this engine off this winter to replace pto and sump oil seal and gasket. When I reinstalled the cables, I only put them back where they had been for the last 12 years and didn't check anything. When I bought this Dixon mower it was remarked that it was cold blooded. Maybe not anymore, started in under 5 seconds after sitting for a few days.