Your idle speed screw is just that, it opens your throttle plate to allow more air increasing vacuum and thus increasing the draw of fuel the jet will let out. Does the bike transition from low to high speed smoothly under acceleration? When you let off the throttle after the HS jet has start metering does your bike idle back down smoothly? If it it hangs for a second and then idles down your high speed is slightly to lean if it drops to a nice idle and the idle increases your low speed is slightly to lean.

Also have you adjusted your idle and low speed together properly? You want to start with a base line setting on your LS needle, use the idle screw to get just enough idle to keep the motor running and start leaning in the LS needle until your idle comes up, readjust your idle screw to back the idle down and blip the throttle. Repeat until you have a smooth idle and no hesitation in the throttle. You know you have gone to lean with the LS needle when the idle starts lowering and bike feels as if it is going to die. At that point richen the mixture up about an 1/8th turn and adjust your idle you should now be set. I don't know enough about Harley carbs to know how many turns is to much or to little and what the turns indicate but if you go more than say 4 turns out on the mixture screws to get things running right you need a jet change. I would imagine more than 2 turns in from closed would require a change as well, this is something you may be able to find with a google search.

First thing in order I would clean the air filter (most likely not it if you perform regular maintenance) and then move on to disassembling the carb, remove all o-rings (rubber bits) and do a carb dip. Berrymans carb dip is some great stuff and can usually be had for $20 at a local car parts store. It will last you a long time so the cost is worth it IMO.

Blow through all your circuits with compressed air making sure you have a good stream of air exiting.

From here you may as well go through and check your float level, make sure float needle and seat are in good order. You could replace the jets with what you have in it and see if it was a worn out jet. If that still doesn't solve the issue then it should either be your idle or low jets. Increase in size one at a time, reassemble and test the bike, it will be a PITA but you only want to change one thing at a time until a single change fixes the issue. Record all your results so you don't get lost in the changes.

Also may not hurt to check your fuel diaphragms, if they are hard they may need to be changed.

 

Thanks for the tips everyone , and Spanner I havnt had an evo in 12yrs so I prob dont know what one supposed to sound like. I forgot to add that a PO had swapped to a HI4 single fire ing, after some checking found the voes was wired but the vac port was plugged as well as the port on the carb. The module was set on voes/ oem. After making sure it was wired correctly I ran a new vac line and checked all the settings . The bike rides and idles much smoother. I installed new plugs and am now at 2 turns out on the mixture. BTW if I start a thread and dont reply for a few days its because my work computer will not let me post.... sometimes . I've tuned a few bikes over the yrs ,it's been a while tho. Thanks for the help.

 

You owe Schex3x a beer or two