Several days ago I fired up the R80 ST in the garage just to run it warm enough to idle without the choke since I hadn't ridden it in two weeks. Everything was fine for a few minutes then suddenly one cylinder started trying to drop out. Couple of days later checked the plugs - looked good. Opened carbs to check diaphrams and clean out all the passages with spray cleaner. I've had the idle circuit and other stuff get gunked up before from oil vapors from the breather condensing at the carb. Usually the left one. Even pulled the idle mix screws to check O-rings and blow out the idle circuits from that end. Put it back together, rode to full op temp. Tried to set up and synch the carbs and discovered the idle mix screw on the left carb had no effect - closed to wide open, nada. Thinking back through the process, I had failed to clean the idle jets themselves. This evening pulled the idle jet from the left carb - sure enough it was gunked up. Cleaned & reinstalled. Only had time to start it but it sounds right and only needs the sync steps repeated after tweaking the idle mix screws. So the TIP: If the mix screw does nothing, suspect clogged idle jet long with all related passages. Don't just spray it. Easy enough to pull with the carb in place and make sure it gets clean.