My Lawnmower must be a Chevy

I have a 10 yr old Sears mower (forgot if Craftsman), the OHV engine. In winter, I leave it in the sun for a few hours first, when I can. Lately, I need to use starter fluid and/or pump the bulb 10 times. I don't like that it lowers the compression during starting to make pulls easier. Not sure how that works and if it might be part of the starting problems.

Mine also has some kind of manifold vacuum sensor that feeds back to the carb, with a rubber tube under the gas tank. Mine got hot and developed a crack. After fixing that, it seemed to run better.

One data point is I found it can be affected by fuel. My wife had filled the 300D with gas instead of diesel, so I drained the gas/diesel mixture. I thought to use some up by running it through the mower. Worked OK for a while, but eventually got where it wouldn't run without goosing the choke. Maybe I got near the bottom where the diesel was thicker. I understand that in winter they blend gas to be more volatile, so maybe you just need to get a tank of current winter gas for your mower.