yz426 carb issue

[cadelamont]

Hello. This is my first post. I searched for other posts about this but i couldn't find anything. I have a 2000 yz426f. The O ring/wire mod was done, and it completely eliminated the yamabog. Awhile later the bike was running great, then one time I cranked on the throttle and it bogged out. I pushed the bike home, started it and it ran. It still bogged out. I know the problem is with the ac pump because when I twist the throttle slowly it revs up but when I let off it drips/dumps fuel out where the push rod comes through the carb and meets with the black actuator arm. I know a seal or gasket is bad i just don't know which one or what caused this. When the carburetor is off the bike, the stream of gas that is sprayed when you twist the throttle isn't a nice steady stream anymore, almost like there is a little bit of air coming out with the fuel being sprayed. Any help would be appreciated thanks.

[WALKINGWOUNDED]

Sounds as if your accelerator pump diaphragm is ruptured.  On a Honda it's sold as a kit: Oring-Diaphragm-Pump Rod.

[WALKINGWOUNDED]

One thing of note.  As you may or may not know, you can't compress liquid.  So if you use wire for the mod, that's ok, but if you twist the throttle faster than the accelerator pump nozzle can spray and release the pressure being applied, something will have to give, and usually it's the diaphragm.

 

If you use the oring mod, the oring will stretch and give some relief to the diaphragm until the pressure drops.

[WALKINGWOUNDED]

Item #31 is suspect.

 

 

https://www.thumpertalk.com/shop/oem.php?partcategory=899619&manufacturer=7&category=5&year=2000&model=28952

[cadelamont]

Thanks for the replies, I unhooked the o-ring/wire mod and it still does the same thing. Do you suggest trying to get a new diaphragm? 

[WALKINGWOUNDED]

Once the diaphragm is ruptured (torn), removing the mod will do nothing.  Don't know for sure that the diaphragm is the problem, but that's what I would look at first.

[WALKINGWOUNDED]

When you do find the problem and make the repair, you may want to use 1 or 2 rubber orings instead of wiring it solid.

[WALKINGWOUNDED]

http://www.magicracing.com/RD-Power-Pump-2-Accelerator-Pump-Cover-wAdjustable-Leak-Jet-Keihin-FCR_p_4879.html

 

R&D makes an adjustable accelerator pump leak jet. 

 

When you twist the throttle, the diaphragm is pushing gasoline to the nozzle to squirt gas down the throat of the carb and into the intake.  There is a jet in the carb called a leak jet.  This jet lets pressure from the diapragm pressure area, leak back into the bowl.  This leakage is done to control how much gas is squirted on accleration.  Too little gas, and the bike lean bogs on quick acceleration, too much gas and the bike can blubber on acceleration or quick acceleration.  This aftermarket kit lets you adjust the amount of pressure bleed back into the bowl to control how much gas the nozzle sprays on acceleration.  It's a simple turn of a screw, versus taking the carb apart each time you want to change the size of the leak jet.  Besides, that red anodized piece looks good on the carb.  lol 

[rogo1]

fwiw, the o-ring mod doesn't work on our bikes. for those of us with the older style fcr carbs we need to use the bk mod. you can find the directions in the first mods f.a.q. section of the model specific section

[cadelamont]

Actually the o-ring mod did work... It worked perfect, not the slightest bog what so ever. Again thanks for the replies i'm gonna have a look at the bike tomorrow and see whats up.

[frankie_b_jr]

R&D makes an adjustable accelerator pump leak jet.

When you twist the throttle, the diaphragm is pushing gasoline to the nozzle to squirt gas down the throat of the carb and into the intake. There is a jet in the carb called a leak jet. This jet lets pressure from the diapragm pressure area, leak back into the bowl. This leakage is done to control how much gas is squirted on accleration. Too little gas, and the bike lean bogs on quick acceleration, too much gas and the bike can blubber on acceleration or quick acceleration. This aftermarket kit lets you adjust the amount of pressure bleed back into the bowl to control how much gas the nozzle sprays on acceleration. It's a simple turn of a screw, versus taking the carb apart each time you want to change the size of the leak jet. Besides, that red anodized piece looks good on the carb. lol

The 426 doesn't have a leak jet. I believe it was 05 when they started, but I'm probably wrong. It does sound like the diaphragm is ruptured. O-rings or heavier springs (not sure where to find them) will be much easier on the system and save the diaphragm in the future.

[WALKINGWOUNDED]

The 426 doesn't have a leak jet. I believe it was 05 when they started, but I'm probably wrong. It does sound like the diaphragm is ruptured. O-rings or heavier springs (not sure where to find them) will be much easier on the system and save the diaphragm in the future.

 

 

Thanks for the correction.  Sorry for any mis-info.