whos familiar with carbs here?

[redlinedeath]

alright, so i have a 81 suzuki gs550 that i decided to turn into a cafe racer. problem is, after i rebuilt the carbs, one of the little legs taht holds the pin for the float on one side of carb #4 broke clean off. its jbwelded for now, and holding, but i figure since i need to rejet the bike for 4 pod filters and a full exhaust, i may as well get the carbs for the gs650, same carbs with different jets. heres my question. either jc whitney or jegs, not sure which one i saw it in, sells air fuel meter/sensor that consists of a sensor, and a module and gauge for $250-ish, and another for $350ish thats the same thing, but comes with a wide band sensor, module, etc. both include a sensor bung.

my question is this one. if i sync the carbs and get the iddle right by adjusting the idle screws, all that good stuff, after its synced up, you think its possible to run that wideband or other air/fuel system to see where im running for easyer tuning, as opposed to the trial and error jet fitting? like, see where it reads? also, i have to have it on the road to get the reading at certain rpms under load?

also, i hate to be "that guy" and ask everything there is to know about a certain thing, but how do carbs work in regards to air/fuel mixture at various rpm? if im getting a good ratio at 4k rpm, does that mean ill get a good one at 9k rpm, or even at redline?

last off, the bike ran fine after i did a full tear down and cleaning, but torwards the end of last riding season, i pulled off the air box cover, and it started completely flattening out at 5-7k rpm, like it wouldnt accelerate anymore. at all. in fact. at that point, at full throttle, it would slow down more then at it would at no throttle. to my understanding, at this point, i hit a very very lean condition, ran really hot, and was shooting fire balls out of my exhaust when i cut the throttle.

i know this is long and annyoing, and my posts are almost always long run-on sentances, and i apologize, but i finally can afford to get the subie AND slow suzie(the suzuki) up and running!!