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YZ 250 F BOG Help Someone!!!

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06 yz 250 f 178 MJ 42 PJ 80 LJ clip on #3 fuel screw 2.5 , Yes I know your tired of hearing it but this BOG is killing me. Alt 900 ft Temp 40 Rode the bike to warm it up runs fine everywhere else but when I whack the throttle open the bike wants to stall. Have tried the so called " HOT SETUPS " went to 180 MJ 45 PJ 40 LJ fuel screw 2.5 Set pump timing so just misses slide and squirt is 1 sec. Ran the bike and it still falls on its face coming out of corners, almost seems worse. Also would like to know if cutting the screen out of the filter cage has made this run poorly. Never tried it with the screen in. My son works for a yamaha dealer and he called them to ask about the bog, they told him to TURN THE IDLE UP! What kind of answer is that? I just wish someone could help me on this one. I'm real close to taking this thing back. Or if someone has a similar problem like this. PLEASE HELP

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A friend of mine has a WR250 with the exact same symptoms. Another friend and I worked on the bike for him for what seemed like forever trying to get rid of the stumble. We did all of the so called hot set-ups ie. leak jet, needle, fuel screw, PJ, AP timing etc... And just like you, we were never able to get rid of the stumble, and we were also told by a Yamaha dealer to just set the idle real high, something like almost 2000rpm! &%$#@!!

We finally gave up, and I have been working on bikes and carbs for over 25 years, this was the first time in my life that I couldn't solve a carb problem, kind of hurt my ego, but what can I say? I always thought that I would maybe like to have a WR250 or 450 but after this ordeal and after talking to others including Yamaha factory trained mechanics, I can honestly say now that I will never ever buy one! I just don't want the headaches! :applause:

Sorry this is not much help to you, but just letting you know that you are not alone one this one. I truly believe that this is a very poor carb for this particular application.

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the fcr is the same carb used by all the manufactures.when set up correctly they are only beaten by fuel injection.

instead of dealing out hot set ups,i will help you guys get your bike sorted.

making so many changes at once often creates more problems than needed.

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Burned, are people expecting these hi-perf carbs to preform like CV carbs? The next question; i am curious about the removal of the of the FA screen and the effects on reversion. Are there any gains there in a stock set-up or w/just an aftermarket exhaust system? I know your answers are supported by data, so thank you.

ps...any thoughts on running a KN in a low dust environment?

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there are slight gains by removing the screens.i do not run them in my bikes.however,i run kn's or flame proof twin airs.

i run the kn's extreme filters in low dust.1hp gain over foam.

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The manual for my FCR-equipped 03 WR250 says the idle speed should be set to 1800-2000 rpm. As far as helping alleviate the bog, I see this as a critical step. Although this feels like a fast idle, it helps maintain vacuum levels in the carb. This in turn helps suck fuel up the jets, minimizing the bike's tendency to bog. Obviously there are other adjustmens required for tuning out the bog, but don't overlook this basic step, especially in favor of a "hot setup". BTW my bike is completely bogless.

To the original poster, your pilot jet may be a bit rich, depending on your alt/temp. I'd stick with the 42 and tweak your fuel screw for a crisp idle.

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The funny thing is I have worked on many bikes with FCR carbs, was able to idle them at about 1400 -1500 RPM, whack the throttle from idle or low speed and never have the slightest bog or more over no stumble.

It seems that every one of the new Yamaha's have this problem. And after talking to Yamaha factory trained techs that I know, they are all bitching about these bikes too. The same or similar carb seems to work much better on the Honda's and Suzuki's. Does Yamaha's 5 valve head design have anything to do with this? Why do the Yamaha's need to idle higher than some of the other brands? I do know from personal experience that not all bikes with FCR carbs need to idle that fast to run right. What the heck am I missing?

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the yamaha 5 valve is one of the reasons for sure.many believe the 5 valve is henderence rather that a plus.

imho any of the "race bred" 4 strokes with fcr's benefit by running the idle at 2000 rpm.

ktm (long stroke) drz's etc can idle slower.

no offense,but those factory trained techs need to do some jetting home work.

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Hey Burned, I did not try it with the clip moved yet. Do you think I should go back to stock and just try the clip and fuel screw? And what about the leak jet? Am I going about this the wrong way? I am getting the Zip-Ty fuel screw because I think I am going to need it with this thing.

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the easy adjust screw is a good thing.every one should have one.

put the jetting back to stock.leave the current leak jet.

now,once you have the stock pilot jet back in you will need to test it with the fuel screw.

with the bike warm and idleing turn the fuel screw in till the idle drops/misses.then go back out just till the idle smooths/peaks.

this should happen between 1 and 2.5 turns from fully in.less than 1 turn you need a smaller pilot jet.more than 2.5 turns you need a bigger pilot jet.retest once you make the change.

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What do you think might be causing this problem and where do I start? I am also running 100 octane fuel Should I be running 93 ? My 04 ran perfect on 93 octane. Could it be the temp 30-40 degrees indoors altitude is 900-1000 ft. Does the J-D jet kit make a difference on the bottom?

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