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.
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.
The o-ring mod can actually cause a rich bog as well. This happens because the o-ring mod extends the duration of the "squirt" from the AP. Very few carbs need the O-Ring. and of the very few that do need it, Even less of them need the BK mod to go with it. The BK mod stops the pump arm so that your AP only gives a quick one second shot of fuel.
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
When the throttle gets opened quickly, the AP rod is supposed to be pushed down under the force of the AP spring. When you do the o-ring mod it forces the rod down faster. It overrides the spring so that how quickly you twist the throttle determines how quickly and with how much pressure the pump squirts. Inconsistency is impossible to tune accurately.
@@gabekenyon4882 I purchase a used 2003 yzf250 (ran terrible) and removed the o-ring mod. Used pro circuit jetting specs and set the squirt timing. Most people test this while in neutral and get the bog. You must test this under load while riding the bike. My bike bogs crazy in neutral but, has zero bog while riding. It is truly a different bike now that the carb is tune correctly without the o-ring mod.
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.
@@ChuckfromTrueTech Okay, thanks for the quick reply. I found a dimension spec (.100") for adjusting the AP screw, but I'll also check the squirt timing. Thanks, Chuck!
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
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.
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.
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.
@@stevenmollard9807 Yep replaced the gaskets when I rebuilt the carb. No replacing the rubber intake boot they don't make them for single barrel rebel carbs anymore.
Ah, got it. Just figured I’d see if my limited experience could help at all. When I first rebuilt my carb I didn’t realize there was a mid body gasket. Had to remove security screws to get to. It was years ago now though, the rebuild kits back then didn’t include that gasket. As for the boot, you may want to check for cracks anyways and if you find any throw some gasket sealer over it. I’ve also had issues with really old boots that have gone hard. Wouldn’t seal to the carb right and let air in. I put gasket sealer or an o-ring between the boot and the carb on previous bikes to solve that issue.
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.
In a situation where this many changes have been made I usually go right back to stock & start over. If the pipe is the only mod it won’t require much of a change. In my experience the changes FMF suggests are often too big. Usually a pipe might require one size up on the main & an extra half a turn on the fuel screw. Make sure the previous owner didn’t mess with the timing on the pumper too. It should squirt right as the slide opens.
That was the common fix at the time, but unfortunately it usually makes things worse. The accelerator pump is fully tuneable without forcing the mechanism.
It can certainly make improvements. It just means that the carb isn’t set up correctly. The carb has enough adjustments to set the timing & pressure without the o-ring.
Was your AP lever chasing the adjustment screw too? I checked mine and it was, and it was timed properly. That lever is pulled down by spring pressure from the AP pump pin spring, adding the o ring helps a ton
@@ethanclark6859 As you said, the spring is meant to provide pressure to the rod. The lever is supposed to lag behind the screw. Adding the o-ring means your hand is controlling the pump, which is inconsistent and therefor impossible to tune accurately. If you want more pressure, install a smaller leak jet. If you want to advance timing, turn the screw. That will give you consistent, tunable results.
@@ChuckfromTrueTechon my 2010 kx250f the throttle response improved adding the o ring.I prefer the feel of having my hand control the pump just my opinion though
Agree with ethanclake oring mod has been around for many years. Assists with AP pump pin spring pressure giving a strong pressure feed out the AP jet. Leak jet makes no difference when the AP spring is too weak.
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"
hanging idle is usually a lean pilot circuit, try loosening the fuel screw on the bottom of the carb, don’t go pass 2.5 turns, if you do the up the pilot jet
I’m happy to rebuild your carb, but I expect shipping may push the expense past a point where it makes sense. My contact info is on my website (www.truetechmc.com) if you’d like to look into it.
I’m not 100% sure, but I don’t know why you would want more duration. The critical moment is immediately after the slide opens. After that the needle & main take over.
@ChuckfromTrueTech I'm barely getting any flow from the pump. The confusing part is that when I test the pump off the carb there's plenty of supply. I think maybe the upper check valve is letting the pump draw air or something
If it has been sitting for more than a month or two it most likely needs the carb serviced. If the idle circuit is clogged, the rest of the carb needs cleaning too.
![Keihin FCR AP Not Squirting [How To Clean/Adjust Accelerator Pump]](/img/n.gif)
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.
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.
The o-ring mod can actually cause a rich bog as well. This happens because the o-ring mod extends the duration of the "squirt" from the AP. Very few carbs need the O-Ring. and of the very few that do need it, Even less of them need the BK mod to go with it. The BK mod stops the pump arm so that your AP only gives a quick one second shot of fuel.
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
When the throttle gets opened quickly, the AP rod is supposed to be pushed down under the force of the AP spring. When you do the o-ring mod it forces the rod down faster. It overrides the spring so that how quickly you twist the throttle determines how quickly and with how much pressure the pump squirts. Inconsistency is impossible to tune accurately.
Then adjust the ap screw when the o ring is already on. Everyone does that mod still.
@@gabekenyon4882 I purchase a used 2003 yzf250 (ran terrible) and removed the o-ring mod. Used pro circuit jetting specs and set the squirt timing. Most people test this while in neutral and get the bog. You must test this under load while riding the bike. My bike bogs crazy in neutral but, has zero bog while riding. It is truly a different bike now that the carb is tune correctly without the o-ring mod.
I just adjusted mine. Do exactly what he says and no issues.
Great info!
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 haven’t shaved down the rivet. The AP should be timed so it squirts immediately after the slide clears the stream path.
@@ChuckfromTrueTech Okay, thanks for the quick reply. I found a dimension spec (.100") for adjusting the AP screw, but I'll also check the squirt timing. Thanks, Chuck!
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
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.
Exact symptoms of my 2004 yfz450.
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.
It may or may not be the sensor itself. Could be the ECU or it could also be the jetting not jiving with the ignition curve.
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.
Man cannot put a man on the moon. Stop believing in fairytales.
Smart Carb!!
Have you replaced the mid body gasket? That fixed mine. Also, another bike I had similar issues and I found a crack in my intake manifold.
@@stevenmollard9807 Yep replaced the gaskets when I rebuilt the carb. No replacing the rubber intake boot they don't make them for single barrel rebel carbs anymore.
Ah, got it. Just figured I’d see if my limited experience could help at all. When I first rebuilt my carb I didn’t realize there was a mid body gasket. Had to remove security screws to get to. It was years ago now though, the rebuild kits back then didn’t include that gasket. As for the boot, you may want to check for cracks anyways and if you find any throw some gasket sealer over it. I’ve also had issues with really old boots that have gone hard. Wouldn’t seal to the carb right and let air in. I put gasket sealer or an o-ring between the boot and the carb on previous bikes to solve that issue.
Great info. I understand all this including the leak jet but maybe you could explain the leak jet to your audience.
I’ll add it to my list of videos to make!
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.
In a situation where this many changes have been made I usually go right back to stock & start over. If the pipe is the only mod it won’t require much of a change. In my experience the changes FMF suggests are often too big. Usually a pipe might require one size up on the main & an extra half a turn on the fuel screw. Make sure the previous owner didn’t mess with the timing on the pumper too. It should squirt right as the slide opens.
@@ChuckfromTrueTech Experiencing that right now. It contacts the slide when you press the throttle. Need to adjust the timing on the squirt.
👍
@@ChuckfromTrueTech I will let you know my findings. You’ve been a huge help
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
That was the common fix at the time, but unfortunately it usually makes things worse. The accelerator pump is fully tuneable without forcing the mechanism.
Very helpful video Ty very much
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.
It can certainly make improvements. It just means that the carb isn’t set up correctly. The carb has enough adjustments to set the timing & pressure without the o-ring.
Was your AP lever chasing the adjustment screw too? I checked mine and it was, and it was timed properly. That lever is pulled down by spring pressure from the AP pump pin spring, adding the o ring helps a ton
@@ethanclark6859 As you said, the spring is meant to provide pressure to the rod. The lever is supposed to lag behind the screw. Adding the o-ring means your hand is controlling the pump, which is inconsistent and therefor impossible to tune accurately. If you want more pressure, install a smaller leak jet. If you want to advance timing, turn the screw. That will give you consistent, tunable results.
@@ChuckfromTrueTechon my 2010 kx250f the throttle response improved adding the o ring.I prefer the feel of having my hand control the pump just my opinion though
Agree with ethanclake oring mod has been around for many years. Assists with AP pump pin spring pressure giving a strong pressure feed out the AP jet. Leak jet makes no difference when the AP spring is too weak.
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"
finally something made sense.
Hey chuck I know this is an old video but I was wondering if you’d know anything about fcr carb hanging idle on the crf150rb?
The 150RB is a huge pain. It’s just like the bigger version. It requires meticulous care to every detail. A hanging idle is usually a lean pilot.
hanging idle is usually a lean pilot circuit, try loosening the fuel screw on the bottom of the carb, don’t go pass 2.5 turns, if you do the up the pilot jet
Wow so many people doing that O ring mod all for not.
I have this problem
Would you be willing to fix my carb / rebuild it for $$
Thanks Bob
I’m happy to rebuild your carb, but I expect shipping may push the expense past a point where it makes sense. My contact info is on my website (www.truetechmc.com) if you’d like to look into it.
I will get a hold of you thanks
Will a smaller leak jet increase the duration of the stream?
I’m not 100% sure, but I don’t know why you would want more duration. The critical moment is immediately after the slide opens. After that the needle & main take over.
@ChuckfromTrueTech I'm barely getting any flow from the pump. The confusing part is that when I test the pump off the carb there's plenty of supply. I think maybe the upper check valve is letting the pump draw air or something
Hello my YZF250 2002 don't hold idle, clogged idle jet ?
If it has been sitting for more than a month or two it most likely needs the carb serviced. If the idle circuit is clogged, the rest of the carb needs cleaning too.
But Chad! My 04 YZ450F doesn't have a leak jet! It's a sealed path in the carb bowl.