Slant running poor on HOT days.

Probably something with the choke. Test the "vacuum choke pull-off" at the top of the carb. If you don't have a hand vacuum pump to test it, pull the hose, push it in, cover the vacuum tube w/ your finger and see if it stays in. Its job is to pop the choke open slightly the second the engine fires.

If not working, you have to keep adjusting the choke between summer and winter, like I used to do with my 69 slant in my dumF kid days. I didn't know what the choke pull-off was or how to test it. I was so gomer then that I thought the Holley 1920 was complicated. Of course we didn't have the internet like today where all info is a few clicks away.