Got to KEEP pumping it, gently, to keep it running long enough for it to finally idle on it's own and finish warming up without having to tickle the throttle constantly for the first few minutes, or longer. No doubt it has a lot to do with the cam profile, it's got a "mean lumpy idle" when it IS warm, won't idle for squat until then.
1850 series Holleys would not do well in an auto cross high G load cornering scenario, is my guess. Even with mod's, still, I don't think they will cut it. Single carb, road race version, would be the way to go, sigh...