I have a 15 SX with race ecm 44t rear sprocket.
Runs great until recently.
Still pulls great with plenty of power. What I did notice was. On a Saturday it was fine. Went out Sunday & now when I shift to the next gear it gives me an abrupt throttle response. Shift hit throttle & it jumps as it goes into the next gear. Like I waited to long to shift into the next gear. Took out all the free play in the throttle.
I went home & checked the air filter. A little dirty but bot bad. Cleaned it & went for a ride. Same problem. Original plugs 13,000 miles.
But the day before it was fine.
Could it be in the ecm? ??