Jim,
This is without a doubt carburation in nature. My guess is gas expansion due to the hotter weather. Coupled with less dense “oxygen” in the air when it is hot. And your idle circuit may have been set when temperatures were cooler.
First take the air cleaner off before you go out and turn the air mixture screws in and slowly count the turns to see where they are set. GENTLY to a close. A normal preset is around 2 turns out for an engine with no air leaks and in good operating condition. Whatever you had before, turn them out the exact same amount. What carb number is it?
Leave the air cleaner off and go for a drive in the hot weather. Get her good and hot, and bring her back to the garage or driveway. Now get out and see if she will run with a 1/4 turn “in” on the air screws. Turning the air screws clockwise or closing them “leans” the idle circuit out a bit. My guess is this may help. If the engine drops rpm when you do this, then we need to go further. The more you can turn the idle mixture screws in the leaner the idle circuit. Without lowering the idle. Go out now and tell us what the screws are set at now?
If this does not help, it can be a couple other things. With a mild cam you may need to crack the curb idle stop screw to far open and this reduces the effectiveness of the idle mixture screws. Adding a couple degrees of initial advance can help you close the idle stop screw a bit. This may help the idle mixture screws smooth stuff out. A final carb thought may be a bit high on the float level. Now we need to pull the top off...
The more initial advance you can run the better. Is your MSD a vacuum advance type or does it not have one? You should be hooked to the port off the front on the passenger side which is “ported” vacuum on the Edelbrock carb? Now of course we do not want detonation. What octane gas do you run? Higher octane can let you run more advance without detonation. And to confuse you more, if you have a vacuum advance MSD, the vacuum dashpot can be adjusted to vary when the timing comes in to supress detonation.
Above thoughts have questions to answer. Wish you were near me, I could dial this in in about one afternoon!! I run a hobby business helping people tune their cars in!!
Give me (us) more information and we will try to help from afar!!
Rob
