Anti-Ethanol Additives
A site member reports:
A mechanic friend told me his secret: Add a little 'Ethanol Shield' or 'Mechanic In a Bottle' to your gas, and you will never have a problem with small engines. Our mowers always start on the first pull. Always. 'Mechanic In a Bottle' will clean out most gummed up, ethanol damaged carburetors.
Ethanol Shield costs $16: https://www.garynorth.com/snip/1445.htm
Mechanic in a Bottle costs $6: https://www.garynorth.com/snip/1446.htm
I have an electric mower, so I have not tested either product.