Motorcycle Repair: XJ900 Multiple running problems!, vacuum leak, carbies

Question
Hi Danee, I am looking for another opinion on my old 1983 Yamaha XJ900.  The symptoms are: Sluggish acceleration, sooty plugs, sometimes after 10 minutes starts misfiring due to plugs 1 & 4 being sooted up (runs fine again as soon as they are cleaned or replaced), excessive fuel consumption, intermittent hanging idle at 2000rpm.  At times you can see black smoke coming out of the exhaust (obviously rich).  The bike was laid up for some time and the carbies were a bit gummed up, so I took them apart, soaked them and completely cleaned them out (all passages appear to be clear) and set them to factory specs as they were before.  There isn't a vacuum leak at the intake, the carbies are balanced, I have just fitted new diaphragms (old ones had some pin holes in them), timing is spot on and I am in the process of doing the valve clearances (a bit on the tight side).  I installed new rings and the compression is good (150-160psi).  The bike has a new air filter and is fitted with a 4-1 exhaust. Pretty much the only things I haven't replaced are the coils and CDI unit. Can you think of anything else?

Answer
Andy, The thing that bothers me the most of everything you are saying is the hanging idle at 2k. This is one of 2 things. Either a intake leak or the carbs are not sync correctly. Did you spray the carbs boots down with some carb cleaner with the bike running?? Black smoke can also come from this. When you cleaned the carbs did you soak them in a "carb dip"? There is some stuff available thru local auto parts stores that comes in a paint bucket that you can put the carbs right into. I'm not second guessing you just wan tto be sure you have everything right as 1/2 of the repairs I do in my shop are "fix ups" of another persons fix. Follow up with me after you read this as I can walk you thru a process to get you back up and running.