I'll supplement the above suggestions and suggest that you ensure that the needle is properly situated in the suction chamber piston (flush to the bottom of the piston - I use a 6" scale across the bottom of the piston for the needle and needle guide to rest against). 

And for what it's worth, if you get to the point of trying to adjust mixture, remember that the idle mixture screw's adjustment is clockwise to richen and counterclockwise to lean.

HIF carbs are notorious for dry and cracked o-rings in the choke mechanism. They will cause vacuum leaks at high vacuum times. 2 phillips head screws and you can pull out the choke enrichment mechanism and replace those o-rings.

I have no idea what you mean by "very aggressive cam", but from what I've read, high peformance cams generally don't idle well. Maybe the cam's action on the valves (duration? overlap" etc.?) mean the cylinders aren't breathing well at the idle speed you are trying to use, giving erratic/lumpy idle and inaccuate AFR readings.

Another thing is where you ae takng the radings - at the tailpipe?

Do this: at idle hold a paper towel loosely on the tailpipe. If your car runs as well as mine, and I'm SURE it does, if the exhaust system is tuned (ala RC40), then at idle, the paper towel will be pulled in and pushed out with every exhaust beat fro the engine. This is the cylinder scavenging - where the shock wave (not exhaust puff) travels to the end of the tailpipe and generates a corresponding negative (low pressure) shock wave the travels back up to the engine and sucks he remaining exhaust out of the cylinder, leaving a slight partial vacuum that drawin in the next charge with more force than just the descending piston. On my car, it shreds the paper towel in a few seconds.

If ths is what happens on your car, then your AFR sensor is reading the air being sucked in and the exhaust coming out, probably giving a false reading.

Before swapping carbs and generating more issues, get an O2 sensor port welded into your exhaust header and take readings from there. Or check the readings above your idle speed - the needle is pretty consistent in shape and, assuming it is properly installed, it shouldn't produce a sudden drop in AFR going from off-idle to idle.

The other way to check idle mixture is old-school, low tech: just lift the dashpot piston a wee bit an see how idle changes, as told by Haynes et al.

 

Have checked for manifold leaks and capped the vacuum ports for timing advance and pcv without any notable change. This engine does have a very aggressive cam in it, next i"ll see what sort of vacuum it is making at closed throttle. My guess it that it isnt making enough vacuum to run properly at idle. I also have a new Webber 32/36 DGV on hand if the 44 wont cooperate.

Running very lean at idle suggests a manifold leak. A closed throttle generates highest vacuum and will draw unwanted air in making a lean condition, but then even a partial throttle allows enough mixture through that the draw on the leak drops away and the carb is providing the intended mixture.

A low float would drop the fuel level in the bowl. On a HIS type the level in the bowl is nominally the same as in the jet,  but on an HIF the bowl is in the bottom, so the effect may not be so critical. Foat level would more likely caus running problems, not idle lean-ness.

 

This article gives the general tuning. There is also a page for Single carb setups and Dual carb setups.

http://sucarb.co.uk/technical-hif-type-carburetter-tuning-general

The "general Mixture" screw you refer to would be the idle mixture screw! you can only adjust idle mixture on the SU the running mixture is determined by the needle and to a certain extent the spring in the dashpot,

Have a fresh 1380 with a similarly fresh 44HIF that's running very lean at idle. We have a wide band O2 sensor to read the AFR at the exhaust, and help with fine tuning. Currently it reads near perfect when the engine is revved up anywhere from 1000rpm and up, but at idle reads super lean, 40 to 1 or so.  Is  there any idle adjustment on these carbs? All I can find info on is the general mixture screw, which seems to be set pretty well. Perhaps the float is wrong? Any input is appreciated.