Where do I begin....
Ok first of all your carburetor is off of a 1983-84 460 truck engine, and this carburetor was used on many motorhomes and large trucks so your FIRST and BIGGEST problem is that. Not sure what application you are using but that carb is "calibrated" to supply fuel for a 460 engine with a lot of big dead weight behind it. You don't tell us what your application is but basically your 302 is literally "drowning" in fuel at idle.
To make matters worse what you have is a Holley 4180, which is a smog version of the 4160. Everything on this carburetor (and I mean everything) is designed to be tamper resistant and designed to work within a VERY narrow parameter. You can't see the idle mixture screws because they are blocked behind tamper resistance plugs, in order to removed them (according to Holley) they have to be chiseled out of the main body (yes that is what Holley tells us techs and it is no picnic I might add). The 4180 has close limit jetting and they are installed at an angle (to prevent being taken out) the metering block is set up to meter the fuel INTERNALLY rather than like the 4160, and therefore cannot be switched out, They also use accelerator bleed holes, which will also cause you some major heartaches when not installing on the correct application. They also use a two stage power valve and factory tamper resistant choke settings (yep more things that will make you go crazy with your application). Sounds like you may have tried to "adjust" what you could and that has even made things worse for you with this particular carburetor.
This carburetor and all 4180's are designed to operate in a very narrow window of parameters and are very worse case scenarios for transplants UNLESS you pay STRICT attention to the application they will be used on. Of course these carbs because of this reason are dirt cheap and easily and readily found.
BOTTOM LINE, IN OTHER WORDS: IF YOU ARE USING THIS ON ANYTHING OTHER THAN A 460 TRUCK, ROTSA RUCK as scooby doo would say.
The other thing, what type of Offenhouser manifold are you using??? If its the single plane (which is a great manifold, MORE ROTSA RUCK, since is basically a full race type manifold. Offy's are known for higher RPM type manifolds, even thier harder to find dual planes.
So not only are you drowning your poor 302, you have probably got the carb flow messed up from your little bit of adjusting and then it is receiving strong signals from the intake further causing it to idle like a race car.
My suggestion........ Get a 4160 carb (600 CFM) intended for a small block ford, or if you are looking for a cheap carb find another 4180 only off of a 302 mustang from the mid 80's. Look at the offy manifold and make sure it is compatible with what you are trying to do.
If you insist on running a carb that is intended for a 150+ cubic inch BIGGER engine (have you ever seen the difference between the intake ports of a stock 302 versus the stock 460) on a very heavy vehicle, with a race intake manifold, DO NOT EXPECT IT TO IDLE LIKE A PUSSYCAT. ALSO DON'T EXPECT IT TO PERFORM NICELY ACROSS THE BOARD.
Hope that helps,
Good luck,
Bill White
White Automotive
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HAVE A NICE DAY!!!!