My ST3 has been lonely for far too long because I've been working (slowly) to narrow down a diagnosis before bringing her to a shop.
Starts easily, plenty of power, idles pretty good, if hunting around a bit. Under light throttle (cruising or through a turn for example), I can feel the power surging a little, as if I'm making rapid small adjustments.
Even though I drained the tank before winter storage, I neglected to drain the fuel lines. Changed the spark plugs, threw in some techron, and tried a good high speed run int the mountains. After getting back into town, my butt dyno is telling me the problem got worse
So, I sent the injectors out to be professionally tested and cleaned, but at 24kmi, one was only slightly out of spec (3% or so). I also replaced the fuel pump and filter, and found the filter screen on the pump had what looked like a pea-sized hairball right under the pickup. Of course I cleaned the screen before fitting the new pump.
After these changes, it seems the issue is less acute, but its frequency has not changed. A little annoying on the highway, but unnerving when the balance changes in the middle of a corner
I tested the fuel level sender while the pump assembly was out, and noticed the Ohm reading moved around a bit if I wiggled the harness wires near the flange fitting/sleeve. Testing the connector on the sender itself, readings are pretty consistent. Is this harness failing slowly (ethanol breaking down the epoxy)?
What's the next most likely culprit given the bike's age? Vacuum leak somewhere? Other electrical faults