low idle when hot

i have a 73 SB with a 1600 DP, 110 cam, dual weber 34 ICTs, and an extractor exhaust. Also i run a SVDA dist and it is timed a 7.5 BTDC, but it does the same thing with a 009. Its runs great all the time except for when it is hot outside and i go for a long drive the idle will slow down and almost die if i don't give it a little gas then it will runs fine for a minute then slow down again. It only does this when it is hot outside and i have been driving for some time, seems to have less power too. Plugs look good too, i had to go up several jet sizes when i first put these carbs on this engine. Thanks