Well, here we are in April, and what I've found out is that the bike is suffering from the dreaded "YZ250F bog"! Apparently, this is a common problem for FCR carbureted bikes. The problem is fixing it. I've found a bunch of threads on it. And I do believe it is a lean bog, caused by the accelerator pump. I'll have to change the leak, or bleed jet and reset the timing just a tad. But now my question is why does this happen? I think it has something to do with one of the coil springs getting weak over time, causing these adjustments to be made. I initially just tried the O-ring mod, but on his '09 YZ250F, it doesn't seem to make that big a difference. Still get the bog. I believe I need more fuel, but for a shorter length of time. Going to try to go from the stock #80 leak jet to the #50, and set the timing to lag just a tad, as it just misses the throttle slide now when opened by literally a split second