[special-K]

It might be as simple as it takes more fuel to start in cold and you are still getting enough for warm weather. I mean, that is the function of the choke in carburetors, fuel enrichment

I thing to try, if you haven't already, is take the cap off and clean the inside with Lectramotive. It could have carbon but not real bad yet. I watched an old mechanic years ago take my just installed cap, toss it in the trash, pull out one he just replaced, and put it on my truck with a crank/no fire problem on a rainy night. Not all caps are created equal. Things have probably changed, but back then I learned black cap = crap and the colored ones were better bakelite. He put a tan one on my truck and from then on I only used Standard Blue Streak caps (blue). That was back before HEI. I've used black with no issues now, most all are now. Haven't had that problem. But I still only buy quality brand caps