We went for a ride with my buddy, and the stumbling problem became repeatable (from intermittent).
It looked like I have the issue when (the disconnected and heating fuse removed) O2 FI codes go away (which shouldn't go away as I made it permanent. From the manual:
"When the engine load is light like at idling or low speed, the ECU determines the injection quantity by calculating from the throttle vacuum (inlet air pressure sensor output voltage) and engine speed (crankshaft sensor output
voltage). This method is called D-J method. As the engine speed increases, and the engine load turns middle to heavy, the ECU determines the injection quantity by calculating from the throttle opening (throttle sensor output voltage) and the engine speed. This method is called α-N method."
I think that the transition between those methods around 4500-5000 rpm, as when I revved the engine to that rpm range in any gear, and anyhow (acceleration and then hold steady, try accelerate thru it slowly or hard), the FI light stopped blinking and the bike surged with steady throttle, stumbled lightly @ light acceleration, and stumbled hard - almost like stall like if you kill the engine and while engine braking you open the throttle - when I've tried accelerate hard. Always recovered, the more steady I held the throttle the faster. After 3-4 stumbles it even accepted full throttle, but when the speed become steadier from acceleration or some deceleration, the FI blinking came back and only gone away if I tried to stay at or above 4500 rpm -for example cruising @ 4k rpm the FI blinking there always, and no stumbling - it worked fine.
So I think it's the TPS sensor (main) will check that out. And because the manual says:
"Do not remove or adjust the main throttle sensor. It has been adjusted and set with precision at the
"If the reading is out of the range, replace the throttle body assy (see Throttle Body Assy section).
If the reading is within the range, but the problem still exists, replace the ECU (see ECU section)."
kawasaki's solution to either the TPS or the ECU will cost so much money..
But if the TPS, then it looks like the K9 gixxer 1000 have the same (by the pics, & the voltage range in it's manual) TPS sensor(s) like the 10R. Part#: 13580-18G00-000 (if mine shot then first I try to swap with the secondary TPS sensor, then I will look for a used throttle assy but if there's none, or costs too much money, I give the gixxer tps a try)