hey all, i have a 98 wr400 that I picked up for cheap and have been riding a bunch lately. Initially I had trouble with some pretty serious bog on the low end, which would cause me to slam into obstacles instead of wheelying over them. I've deep cleaned the pilot circuit, and the entire carb twice, which helped (barely). I tried safety wiring the accelerator pump to the throttle, which didn't work too well. Finally, I replaced the accelerator pump diaphragm, which did actually help a lot, but i still get some bad hesitation down low.
I've heard replacing with a newer 426 or 450 carb from a YZ will stop the problem, but I don't want to buy one just yet until I'm sure. Has anyone had experience with tthis? Thanks