Originally Posted by XR650L_Dave
It could be a rich or lean flat spot, It's a pain but I'd try fine-tuning the needle shim washer thickness.
I assume you have a 15x or 160 main jet, not a 150...
If it's a rich flat spot, riding without the airbox cover should help it, if it's a lean spot that'll make it much worse.
When I whack my throttle open I suspect I'm a touch rich, it burbles for a brief moment before pulling but the power doesn't go down and then back up, it just pulls a bit harder, it clears, and then pulls as it should. I tolerate it because for my riding, the control seems good and I'm just too lazy to mess with it.
Right..my typo, its a 160 main. needle shim is .025". I'm at sea level.
Air cover trick is going to be tried this afternoon.
What effect does cutting the spring have? Cutting 1 1/2 coils was part of the "carb fix-it recipe" for my KTM LC4. That thing rocked afterwards.