FCR Lean Bog Fix (It's not what you think) How To 

Man can put a man on the moon, but he can't design a carbuerator that isn't total shlt. I've got a lean bog I've been trying to fix for 5 F'n years. I've taken this thing on and off and surgically cleaned it out a million times and been all through the accelerator pump and every jet. There's nothing simple about solving carb problems, at all, ever. I've never had a carb that you just cleaned and it just worked.

Float height is also important, I've been bitten by several hasty rebuilds where the float is too low and the pilot jet isn't able to suck in the fuel it needs.

Good info. I've got a WR450f project I've never been able to get running right with the symptoms you've described. Hope I can get it back running right.

The o ring mod doesn’t necessarily advance the timing, because the AP timing screw sets when it will kick in. All the o ring does is put spring pressure on the back of the AP lever. If the AP timing screw is set right, you won’t see an issue with the fuel hitting the plate, all that will happen is more fuel gets to the cylinder in a faster stream

Great info!

If it’s rich and not lean like this, feel like you hit a rev limiter and not a power band ? or if pops on deceleration and shoots flames, and exhaust dumb hot - yea cuz combustion is occurring in the pipe need to have more AIR to lean it out, move needle down /put the clip up & Change the main jet for full throttle Pillot jet is for 1/8-1/4 throttle Needle is for 1/4 - 1/2 throttle If you went up or down too and it gets better till the end- get a new red or blue needle and begin clip in middle. Also check the exhaust and intake cam valve shims.

Great info. I understand all this including the leak jet but maybe you could explain the leak jet to your audience.

Years ago when 4 stroke mx bikes first came out 98-early 2000s the o-ring mod was absolutely "mandatory" if you didnt want a bog

How does the idle adjustment that pushes on the throttle disc play into squirt timing? Do you set the idle first as it will turn the throttle disc as if throttle was being given then set the squirt once thats dialed in? Have my FCR 41 tore down starting from scratch and this is the one area im not as familiar with. Great video

Thanks for this quick video, Chuck. So how do you properly "time" or set the AP screw? Also, have you tried shaving down the rivet on the diaphragm from 4.5mm to 2mm? Supposedly it helps the 06 CRF250R.

I have 2004 crf250r and that "black thing" you mentioned what Is that and the screw that sits in the spring called? because the diaphragm needle that sits in it doesn't wanna go back into that "black thing" on my carburetor, any idea why that is? the throttle drum moves but not the "black thing"

If you have weird off idle issues, try to disconnect the throttle position sensor and see if it makes a difference. I was chasing tail trying to diagnose idle/ off idle issues, once the sensor was disconnected all the issues went away. Now I need to figure out what's wrong with the sensor.

Dealing with this right now on a 2013 Honda 450ER. Guy before me jetted it for a pipe but no open intake, ran awesome but that bog has always been there when you stab the throttle. Main jet:128 , pilot 45 , needle in middle position (stock position), accelerator was as a 58 which is weird, because people preach a 50/55. Fuel screw 1 whole turn out. Still bog. Weirdly enough, now there’s a bog at 3/4 - WOT.

finally something made sense.

The o-ring mod using an actual rubber o ring made a huge improvement on my fcr. Stream does not hit the plate at all.

But Chad! My 04 YZ450F doesn't have a leak jet! It's a sealed path in the carb bowl.

I have this problem Would you be willing to fix my carb / rebuild it for $$ Thanks Bob

Hello my YZF250 2002 don't hold idle, clogged idle jet ?

Will a smaller leak jet increase the duration of the stream?