In gasoline there are over 14 different fuel molecules each with a different boiling point. The lightest boils at 95*F, the heaviest at 395 or something.And in-between are many different boiling points. If it boils at 95, you can imagine at what temp it begins to evaporate.
The lightest are in there, it is said, to help light your engine off.
The heaviest are like adding mix to your bar-drink, it slows things down.
But I suspect there is/are profit related reasons to put the very light and the very heavy molecules in our gasolines.
Gasoline, outside the combustion chamber, requires a very limited AFR to lite off; if too rich or too lean and it won't lite. Each of the different molecules has it's own characteristics. After two or so days, the lightest VOCS in your vented carb are gone, and what's left is difficult to light... plus the liquid level is now lower in the bowl, making "pull-over" harder.
You gotta understand that the carb does not suck gas.
The piston,falling on the intake stroke, creates a low-pressure area in the cylinder, which the higher pressure atmosphere then tries to fill. Air always moves from a high pressure area to a low pressure area.
As the air is moving thru the venturi/throttle bore, atmosphere is also pushing down on the fuel in the fuel bowl.But with the liquid level in the fuel bowl now lower than design, and the fuel itself now heavier, there comes a point where the atmosphere can no longer push the heavy fuel to the top of the idle wells, and so even if you could start it with enough pumpshots; until the liquid level comes up, the choke blade and venturis will not provide enough pressure differential, especially the 1bbls, to sustain running, and the engine is being forced to accept the syrup before any good stuff gets there.
If your car sits in the sun for hours, it's just so much worse.
Your fuel will benefit from installing fuel-stabilizer. Up here in Canada, Shell gas is advertised as having it added, and I find shell 87E10 to be better than other brands.
Underhood heat is also an enemy of the carb. I run fresh air into my carb, and I pop the hood when I pull into the gravel-floor carport, on the North side of my 2-story house. It's always so much cooler under that roof.
As for me:
As others have mentioned, I too keep a small bottle of stabilized, 5% 2-cycle mixed gas, under the hood.... just in case. I mix the oil in there to help maintain the ring-seal during cranking, to help the rings create the high pressure differential, that will encourage the atmosphere to get the heck moving. That's another reason I have an 11/1 Scr engine. And I run a Holley DP carb. It has TWO accelerator pumps, NO choke, and a dash-mounted, dial-back, ignition timing box with a range of +6/-9. So I rarely have problems.
And finally, your engine has a carb heating system on it, that forces hot exhaust gases to move from one exhaust manifold, to up under the carb,and to then exit into the manifold on the other side. The thing that causes this to happen is usually called a heat-riser valve.It's job is to be closed when the engine is cold, to help the cold-engine run better, and to open as the engine warms up. Well, they tend to seize up and if this happens at any other position than wide open, then the hot gasses tend to cook the carb, making it run hotter than it should. Then when you shut the car off, the hot carb boils it's gas away.