Don't blame the Holleys. Maybe the last time that you parked it all the heat under them boiled all of the fuel out of the float bowls and flooded it. (all 3 bowls) The next time you try to start it, there is too much gas in there and it doesn't start till it leans back out. Did you install the 1/4" thick heat insulator gaskets under the carbs? I bet that you only have the paper thin ones under yours.
Next time that you know that it'll be a problem starting, pull the air cleaner first and work the throttle by hand while looking into the bores. See if you get a pump shot out of the squirters. If you do, then try to start it. If it still doesn't start right away, it's flooded. Hold the throttle to the floor to get more air in there.
If you don't get any fuel, start cranking because the bowls are empty, and still could be flooded.
I've also had those rubber tipped needle and seats stick closed on me. Get one without rubber.
Rob