I think I would first start by looking at the vacuum lines. The line between 3 and 4 is famous for going bad. Take a good at the vacuum tap caps also.
Also draining fuel from each carburetor would be a good thing to do. Each carb has a drain screw.
Didn't want to hijack "Sounds like running on 5 cylinders" but had to let you guys know that you made my 98 Tourer run like a new engine. Patrick posted the above quote a couple of days ago and it stuck with me. My Tourer has 125K miles and gets 35-40 mpg so I'm pleased with it's performance. Guess I became used to little things that weren't right. In the garage I looked at the vacuum line Patrick noted and the end looked ok. Raised the plug wire that was laying on top of the line and there was a hole worn by the 2 lines rubbing together. Did a temporary patch and soon as the bike started I realized I had a problem all along but now I had a new sounding engine
Noises that were made when I'd back off the throttle were gone. Can't wait to plug in a new line or probably several new lines.
