Join Date: Oct 2017
Location: Lehigh Valley, PA, USA
Model: GL1200 Interstate
Thanks for the posts. Before reading them, I got to thinking what happened with the bike.
The bike ran fine until last week when it began a rough idle. Yesterday, I adjusted the idle mix screws and found a bad spark plug terminal on #3 (which was probably the reason for the bad idle...should have stopped fixing things right there). But since the mix screws were re-adjusted, it seemed easy enough to re-balance the carbs again.
Well, the first CarbTune reading had two pairs of carbs in sync but the pairs were not in sync so I began adjusting them. While adjusting, I thought to myself "this isn't right" because I kept backing out the base idle screw. Even to the point where I thought it might back all the way out. So I stopped. That's when I found that the idle return spring on #3 had detached itself.
Because the spring wasn't engaged, it allowed the two adjuster screws on that side (right side) to move ever so slightly on the throttle shaft when applying pressure with the screwdriver to make adjustments. That little bit of movement threw everything out of whack - three adjuster screws and base idle screw. Each (false) adjustment compounded the problem until things are as they are now.
I'm confident that Dave, RedWing, etc. hit the nail on the head, now that I've had time away from the bike to collect my thoughts and your thoughts. I've not gotten out to the bike yet today...will get there later today...but I'm sure that's what's going on. Thanks for all the help, including how to fix it (and the long explanation Redwing...that brings it into focus for me). Slow steps and minor adjustments should bring #4 and the others inline with each other. I greatly appreciate it. I'll report back after I get to the garage and spend a bit of time with it!