Is the fast idle the one where it's touching then cam?
Yes.
Haven't messed with too many Holleys (don't like 'em...but, that's beside the point), but have set a few. 2280...four barrel, or what?
Anyway, first make sure your float adjustments are right. That is a must. Once that's done, to mixture/idle speed. Got a tach???
Understand your idle speed affects mixture settings, and the other way. Idle speed about 600 RPM (if not less).
Need to carefully watch the tach while making mixture adjustment. Between too rich, or too lean, you'll get less RPMs at the tach. Start by turning ONE mixture screw out (rich), watching the tach. If the RPMs move down...too rich, if they go up...too lean. Do only a 1/4 turn at a time, letting the mixture settle in, letting the RPMs settle.
The right mixture is where the RPMs peak (at idle speed). There will be a short 'range' where the RPMs peak, then start to fall back down.
From what you say, probably too rich, so you'll need to lean (in) the mixture screw. And, if the idle speed goes too high, you have to re-set it! If idle speed goes too high, mixture setting gets tossed out the window!
Once you get ONE mixture screw adjusted, do the same for the other, exactly. Once that's done, and idle speed is correct, shut the engine off.
Then, carefully, one at a time, turn each mixture screw 'in' gently seating it, AND counting the turns of the screw. You want the exact number of turns for each screw, and if ANY difference, to 1/8 of a turn, split the difference between the two. Then, turn each screw back 'out' that exact number of turns, so each one is the same turns.
Also a good idea to re-check your timing.
