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The O-Ring Mod for an FCR

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what if the O-ring isnt exactly 7/16" x 1/4" x 3/32" but is slightly bigger. will this still accomplish the same thing? the O-ring I have fits but just slides right over doesnt need to be stretched really hard with needle nose.

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what if the O-ring isnt exactly 7/16" x 1/4" x 3/32" but is slightly bigger. will this still accomplish the same thing? the O-ring I have fits but just slides right over doesnt need to be stretched really hard with needle nose.

Then that ring is too large. It must hold the two together firmly.

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I might be reading the catalogs wrong, but I find that specific size O-Ring to be a #108. #78 is not listed.

In any case, thanks for the write up and pictures.

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Hi Guys,I have just fitted the JD kit to my 530 EXC and found using the exhaust spring puller tool to be very effective.It,s best done from entering behind the frame near the shockie.It eliminates the risk of pinching the O ring with pliers.

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Time to add some related information.

Now that you have the O-Ring mod done, there is a few other things. Now, you bought a box of the O-Rings, they will probably out last your bike, but being rubber, over time they can crack and stretch. A more permanent solution is to replace the AP spring with a stiffer one. I used the one from Merge Racing. However, you must remove the carb from the bike to do it. If interested in this, take a read of the write up I did in the Products Review forum here:

https://thumpertalk.com/forum/showthread.php?t=664999

Now to the matter at hand. If, after doing the O-Ring or stiffer spring, you still have a bog, the next thing to check is the squirt timing. The screw you slipped the O-Ring over is the AP timing screw. Screwing it in makes the squirt occur sooner, out, later. What you want to happen is to have the squirt just miss the slide. On some bikes, you can pull the airboot off the carb, fold it behind a frame tube or something and look inside the carb throat. You will see a small brass tube sticking up, that is the AP nozzle. With the carb bowl full of fuel (ideally, fuel tank on, petcock 'on') nail the throttle (engine off, of course). You will see the squirt. If the slide rises and the squirt misses by a mile, tighten the AP timing screw 1/2 turn. Misses still, but only a half mile now? Tighten again. Keep doing this till the quirt just hits the slide, then back the AP timing screw off just enough to miss. If the squirt was hitting the slide, then simply back the screw off, again, 1/2 turn at a time. Once it clears the slide, tighten it back in till it just hits the slide, then back it off till it just misses. If you have to loosen/back out the screw a lot, ensure the spring on the screw still has tension. If not, the screw could vibrate out and cause all sorts of mischief. If need be, you may have to either shorten the screw or source a shorter on. If you do remove the screw, take great care in counting the exact amount of turns you had to use to remove it. Then on re-install, use this value to get you back .

Keep careful track of the exact amount you turned the screw written in your jetting records.

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I've just fitted my fcr a couple of days ago, and had a hell to get it into both airbooth and intake. Probably twisted and turned the carb in so many ways that the o-ring slipped out. Didn't notice any difference ,so my fcr doesn't seem to need this mod. The squirt didn't hit the slide either,so is was probably set ok by the factory.

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This apples to Non FCR-MX carbs. The MX series does not use a leak jet.

Now that you have either the O-Ring mod or stiffer AP spring done, properly set the AP timing screw, you can mess with the leak jet.

The leak jet 'leaks' fuel into the carb bowl. The AP chamber holds a set amount of fuel. You nail the throttle, the AP mechanism presses on a diaphragm pressurizing the fuel in the AP chamber, causing it to squirt out the AP nozzle in the throat of the carb. Gasoline, like drinking beer, it is possible to have too much of a good thing. You want just enough fuel to satisfy. So to prevent the entire contents of the AP chamber from being squirted in the carb, the leak jet 'leaks' an amount back in to the carb bowl.

Next, you have decide if you need to change the leak jet. The obvious clue is the bog still is apparent. You cannot test this in the garage, nailing the throttle from idle. Believe it or not, you never do that when riding, so testing must be done under normal operating conditions. Being there is only one leak jet circuit, you must set it with some consideration. If you are a slow woods rider like me, you need to focus on low rpm response. If you are some hot shot A class whipper snapper, you may need to focus on High RPM riding.

For slow riding, the engine needs a larger amount of fuel, for fast stuff, less.

So, for us 'stately riders', as we are experiencing a 'lean bog'. To increase the amount of fuel, a smaller leak jet is called for. You want less fuel to 'leak' back into the bowl, more to squirt out the AP nozzle. Many riders have been happy with sizes as small as #40 and as large as a #60.

For fast riders (g-damn kids ought learn to slow down, by gum) you need a larger leak jet. You want the total squirt out the AP to be less, or else you could suffer a 'rich bog'. Most bikes come with a fairly well sized leak jet for these guys. Typically from as small as a #70 to as large as a #110.

If you ride both slow technical stuff and high speed open MX, then you should err towards the slowest riding you do. Bottom line is, you want the largest leak jet you can run without the dreaded bog.

Now, swapping leak jets is a huge pain, on some bikes, it can take close to an hour to do. Because of this, an ALJ (adjustable leak jet) is just the ticket. You remove the AP cover and install the ALJ. I have tried two different ones.

I used the R&D one, simply bolts on, no modifications, completely reversible. The adjuster screw points to the right side of the bike. For me, this is right where my exhaust was. I do not like being burned. But it is a straight bolt on. If you have little clearance under your stock AP cover, the R&D one may not fit.

I then acquired a Merge Racing one. This one is not a straight bolt on (you must drill the float bowl on a drill press, a jig is included to make it error proof) and although installation is not reversible, it takes more effort to do so. The adjuster screw comes out on the left side. Finally, it is barely thicker than a stock AP cover so clearance issues should be minimal to non-existent.

Both ALJ's work the same, the adjuster is much like a fuel screw on a FCR. Screwing it in effectively makes the leak jet a smaller size.

Again, any time you swap a jet or tweak a adjustment screw, keep careful notes.

Addition:

Some time to get the squirt to exactly 1 second. This is nearly impossible to do with a stopwatch. So.. what some guys do is use a video camera to record the operation. Using a 30 FPS camera, they record the squirt. Then, playing it back on a computer, they count the number of frames from start to finish. A 30 FPS camera would mean a count of 30 from squirt start to finish would be a one second squirt. A count of say, 45, is a one and a half second squirt.

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I recommend using snap ring pliers. It took me start to finish about 1.5 minutes to install the o-ring, that includes removing the cover to get to the pump cam. :lame:

432snapringplierset2008.jpg

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Hi William,

To start with: great articles, tutorials, and info. Please keep producing these great pieces! 👍

Now, I think I have to disagree with you on this:

The screw you slipped the O-Ring over is the AP timing screw. Screwing it in makes the squirt occur sooner, out, later. What you want to happen is to have the squirt just miss the slide...

To my opinion, screwing it in (clockwise) delays the squirt; screwing it out advances the squirt.

If you screw it in, you rotate the pump linkage anti-clockwise, which lifts the pump linkage rod (going to the membrane). Therefore, if you hit the gas, it will take longer for the rod to touch and compress the membrane --> delayed squirt.

I changed a picture from another thread for clarity:

ap-rod.jpg

What do you think?

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Alright, no thanks 👍

I was pretty sure, and now you made me think about it again (so it was for a good cause).

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William1 and others, thanks for the posts.

My sons 06 CRF250R has some bog even after the Quickshot2 install.

I plan to do the o-ring mod and check the squirt timing to see when it hits.

Do you by chance no if the 06 CRF250R is an FCR-MX carb and i need to be concerned with leak jet or not.

Thanks in advance for replies.

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Yes, it does have a leak jet. Stock is a #55, I think.

Sadly, too many people are caught up in advertising that claims to fix a issue that proper jetting for a few dollars and some time would cure.

Do the oring and check/set the AP timing. Confirm the leak jet is a #55, if it is, it should be small enough.

Does your son ride tracks only or does he just plunk along the trails?

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Yes, it does have a leak jet. Stock is a #55, I think.

Sadly, too many people are caught up in advertising that claims to fix a issue that proper jetting for a few dollars and some time would cure.

Do the oring and check/set the AP timing. Confirm the leak jet is a #55, if it is, it should be small enough.

Does your son ride tracks only or does he just plunk along the trails?

I need to verifiy what stock Leak is, have not checked it yet. He is moving up from CR105 SuperMini MX and does ride in the woods hairscrambles. We are getting the bog and i ride it some too and have the same issue. I guess i am used to the 450.

As far as the 06 CRF250R, sounds like i just need to do the 0-ring mod and set the AP timing to fire just after the slide open where it almost hits the slide. Some others reported running a 45 Leak jet in the model. Thanks for your responses, info is greatly appreciated.

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Hey William1, Great Job!!!!

I got a question for you, though. When installing the Merge AP spring, you mentioned the float bowl needed to be removed to disconnect the pushrod from the cam. I tried both of Merge's methods (prying with screwdrivers and removing the float bowl to pull on the pushrod) today and quit before I broke the plastic cam or bent the metal pushrod. What is a good way to separate the ball on the end of the pushrod from the socket it connects to on the cam?

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Hey William1, Great Job!!!!

What is a good way to separate the ball on the end of the pushrod from the socket it connects to on the cam?

Wrap the end of the pushrod (which sticks out besides the float-bowl) in a towel and use pliers to grab and pull the rod out. The towel is to prevent it from damage. You will get it out, but it clamps in pretty good.

You can put it back in, pushing against a table or so, while securing the black lever in place with your thumb.

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Hey William1, Great Job!!!!

I got a question for you, though. When installing the Merge AP spring, you mentioned the float bowl needed to be removed to disconnect the pushrod from the cam. I tried both of Merge's methods (prying with screwdrivers and removing the float bowl to pull on the pushrod) today and quit before I broke the plastic cam or bent the metal pushrod. What is a good way to separate the ball on the end of the pushrod from the socket it connects to on the cam?

I slip a small jewelers screwdeiver in the cam just above the ball end of the push rod. Pops out easily and no chance of marring the finish on the rod.

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