This is probably going to sound pretty dumb. Bear in mind I think I have jetting OCD, and I desire a lot of throttle control for slippery woods riding.
I've been fooling with my jetting, and am running a different needle with a slightly (correction) SMALLER root diameter.
I'm getting a slight stumble at 1/8 throttle that I can't clean up. Off the pipe it manifests as a 'tat tat tat', until the motor snaps to life. On the pipe, things work pretty well, with only a slight hesitation.
I've heard that 'tat tat tat' called "four stroking". Is that caused by a rich condition, (a lean condition?), or is it just a byproduct of the engines porting design and being off the pipe?
I tried many air screw settings, and the further in I went, the fatter and worse the issue was. I tuned the air screw out, and it worked best at 2 to 2 1/4 turns, so I put in one size smaller pilot. It helped, but didn't make it go away. Still running the air screw around 2 turns out. (Keihin PWK, FWIW)
Bike runs clean up on the pipe, and will come down very cleanly when you chop the throttle from a high speed top gear blast. I think I am close, but not quite there on the jetting. What would you do??