Those older gas engines don't like the new Ethanol blended fuels, especially after they've got a few hours on them and they start getting a little loose.
Ethanol (and all alcohols) really like absorbing water, and unlike gasoline or other oils, they keep it in solution. With the temps up & down condensation is a sure thing.
So, you add an older engine with lower compression, add poor alcohol-blended fuel that contains a good portion of water. A poor starting engine is the result.
There are lots of additives out there designed to fix this problem, check at your local auto supply place, even the auto dept. of Wally World and such will have products for this.
Your best protection though is to just keep the tank full all the time to limit the condensation from forming in the first place.