Discussion in 'General Tech' started by MXracn746, Jan 31, 2017.
This may sound silly. But it works. Take the carb apart. Boil the carb in carb cleaner.
Bike's running great, but the popping/backfiring is still there. It's the aluminum sleeve on the exhaust. FMF sells them for their exhaust for $20. Ordered a couple.
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
Hey one other thing to look at is the plate on the carburetor slide, it is removable and can be installed upside down, causing a lean condition. Only reason I know/ am suggesting this is I just had a bike through the shop that had this issue. It was running super lean and had a big bog. It was on a Honda and on that bike there is a hole in the plate that mounts to the slide and the hole needs to face down so that you can see it. Pry not your issue but something to check. The plate looks like it should go the opposite way that it actually should.
I'll look at it here in a bit. No one in central Ohio has any leak jets but Lancaster Sports Cycles. Picking up the only one they have, a 50, in the morning.
Put in the # 50 leak jet, turned in (put in more delay) the screw on the cam. Turned it CW one turn. Used the O-ring mod also. Tried to do all that and take off the O-ring, and didn't help as much as with the O-ring on. So I left the O-ring on. Bike ran good. This is a common problem with the FCR carb from what I understand, and seems to me that there isn't a clear cut answer to them all.
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