Care to explain the o-ring placement in the AP circuit for the WR-400 to me?

For $500 I'm not even remotely interested in something I can fix on my bike in one night.

For $500 I'm not even remotely interested in something I can fix on my bike in one night.

Been there, done that, and ended up with two 450 carbs on my two WR400s. Got them each for between $150-$200. Good luck with that carb. It's a POS IMHO.

Do the 450 carbs swap over that easily, and are they that much better?

The new style FCR MX's do have a superieor AP and a more durable slide. Keep in mind, a used carb is well, a used carb. You should throughly inspect it (esp the carb body where the slide wheels ride) for excessive wear and neglect.

Hmm... well I'll see if this fixes my issue. Outside of the bog the carb seems to be in excellent shape to me...

Once you get the AP setup, the Slant is a good carb and worth using. Its' faults are slides prone to cracking and the AP push rod has been known to seize (but only on carbs that are negelected).

I would not rush out to get a FCR-MX but keep it in the back of your mind. If you stumble on one that is cheap and in great condition, scarf it up.

Welp, I took my bike out for a short 15-20 mile shake down ride today on some fairly mellow terrain I know really well. The bog is GONE! Dead done and over with! Damn does this fix work!

I'll get all the proper pictures together and create a writeup!

where is your write up already.

the motor is in my bike, and waiting for cams.

i went to put the carb on and was liek, wait...need to wait for jincolas write up on either to use the taffy, or safety wire.

i have 05 yz fcr-mx(ap internal) i believe.


Put the bike back together and took it out shredding! MAN does it rock! New suspension and linkage/swingarm bearings feels pretty damn good. The biggest difference though came from performing the Eddie mod to my carb. NO MORE BOG! The bike is way happier to stand up now in every gear, from any place! BOOYA POWER!

Here is the jist of the eddy mod, before I do a full write up:

With the carb removed, you'll first want to locate your accelerator pump linkage. If you were sitting on the bike, it's on the riders right hand side of the carb. The linkage in question looks like this:


Give the throttle a few twists (manually since the carb is off the bike) and you'll notice that it moves this linkage. The problem over time is that this linkage wears, and to begin with it was outputting way too much.

The solution:


See what is circled in red? Those two pieces are actually separate. What you need to do is WIRE THEM TOGETHER using safety wire. Here is some work another person did to safety wire there's together:


I personally did mine a little bit better (PICS TO COME). I took a very small drill bit, just big enough for my safety wire to fit through, and drilled through both of the parts needing to be safety wired together. I left enough room around the hole of course that their strength wasn't compromised. I then, using my safety wire tool, tied them up properly with safety wire, not just a loose knot like here.

That alone however is not enough, that is only half of the job! Now the accelerator pump is tuned right in with the throttle, which yes is helpful. However you now get a longer stroke on the accelerator pump diaphragm. The two pieces you just wired together, well when you turn the throttle it pushes down on a rad that goes into the bottom of your carb. THAT is the accelerator pump, and inside of there is a diaphragm. It looks like this when taken apart:


Now there are two diaphragms in that picture. Only one is in your accelerator pump. The left diaphragm (it's black, far left piece is the cover for the accelerator pump) is shown with the top facing up. That is absolutely fine, leave it alone! The one on the right is the bottom, and it is NOT fine! That's a stopper, and what'll happen is if you leave it stock, and open your throttle, the linkage will push down on the diaphragm, and it will hit the stopper before you've reached full throttle. This will cause binding, and it will eventually damage something if you don't fix the issue!

The solution to the binding linkage issue: GRIND OFF ALL OF THE STOPPER ON THE BOTTOM OF THE DIAPHRAGM (protrusion sticking up on the right side diaphragm). I ground mine off with a dremel no problem, and in no way did I nick the diaphragm. It's very easy.

With that removed, you now get full action on your accelerator pump, a reduced squirt amount and time (which was the initial cause of the bog) and all should be well!

There is one other thing to check still though!

It would appear that more often than not this doesn't require tuning, but it has been documented so I want to share. This is the archaic fashion in which you adjust accelerator pump on the FCR pumper slant carb.

Put the carb back together, and put it on your bike, with the throttle cables hooked up. Don't put the airbox back on yet, and only place the gas tank on loosely. We simply need to be able to get gas to the carb. Fill the float with gas, and now you'll want to give the throttle a quick twist while looking into the carb. Use a flashlight if you aren't in a bright location.

You should notice that the slide moves up, and almost in sync with the slide raising, gasoline is squirted past where the slide used to be. That is your accelerator pump in action.

Now, if your squirt is HITTING the slide as it raises, it is squirting too early. The fix for this is to take the plastic arm in the top most picture (you just wired it to the linkage from the throttle) and BEND IT CLOSER TOGETHER. Yeah... it's old school I know and not precise, but just keep bending it closer together until you can finally thwack open the throttle, and squirt gas past the slide, not directly onto it.

From my research having to do the above seems pretty uncommon. I didn't have to do this. It is documented however, so I will share this with you!

That's the jist of the modification. This is currently just all the pictures and information from other threads assembled however, based upon my experience performing this modification myself.

where is your write up already.

the motor is in my bike, and waiting for cams.

i went to put the carb on and was liek, wait...need to wait for jincolas write up on either to use the taffy, or safety wire.

i have 05 yz fcr-mx(ap internal) i believe.

Different cab, you have the MX variant, JNicola has the slant style.

You just oring/wires(check for binding)/replace the cam spring. No taffy mod on the MX.

The taffy mod is jenky compared to the Eddie mod!

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