You can clean it and hope. It's a Holley. Adjustments seem to be their thing. And it seems like most list that carb you have as a 'track' carb, i.e., it's fer racin'. Probably means nothin' though.
If the cleaning and resetting (maybe rejetting?) doesn't fix it, I'd check out the Autoline F22100. You just literally throw those on, adjust idle air, and you are done, just run them once a week to keep them from gunkin' up. Or so all the two FoMoCo/Autoline carbs I've put on my machines were. Rockauto has them for pretty cheap, ready to bolt on, and they're called for on the 289s and 390s.
It could be the floats, though, causing fuel level issues. You can do the hot water test. Get some hot water in a vessel big enough to have it and the float in it and not overflow, plunge a float into the water and watch. If there's bubbles coming out of the float, then the float is bad, and you need a new one.
Just get a rebuild kit with the floats in it, and that will solve it all... if it's just a rebuild needed. It could be "that's just a Holley for ya", like it was on the ones we had in the family.
This assumes the compression is good in all cylinders and you don't have any air leaks in any of the intake manifold or such. Perhaps sprayin' some wd40 around will help you find any of those air leaks. That could very well cause this kind of thing too, and will drive you nutz.
/maybe it was us.
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