Idle way rich

Yeah, timing first.
Try it the other way round, then when it just wont come to ya, go back to timing, and start all over. Why not just ballpark the timing first? Learned that decades ago.Got a real surprise when I first learned about throttle controls on 2-cycle outboard marine engines.
-The absolute fastest way to get rid of the idle-stink, is to; crank in the timing, sync up the transfer port, fine tune the idle speed with, if you really have to, the secondary cracking screw ,block the v-can and bump the fast idle up to around 2000-2200 (where ever the cam vacuum peaks), and fine tune the idle mixture screws to the rich side. Drop the idle speed back down and, maybe, readjust the mix ever so slightly.This assumes the float level is correct and that the power valve is not dribbling. Finally, reset the A-pump, and reconnect the V-can and tune that.Doing it this way has the distinct advantage of usually preventing/curing any idle tip-in issues.Theres only one caveat; It helps to correctly guess/set the initial timing reasonably close the first time. This number varies, mostly, with cam design and Dc/r,and sometimes carb selection,Oh and as crackedback is going to mention, in post#25; with starter kickback.
-Holleys arent known for their stellar low speed operation.
So, if youre a newbie, you can take most of the guesswork out of the equation, by following the advices above given by old-timers,tuners and regulars, and you will be well on your way to stink-free idling and issue-free motoring.