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The O-Ring Mod for an FCR

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Hey guys, when you say the squirt should miss the throttle plate, you mean the firts one or the vacuum release plate? the first plate is a bit higher then vacuum release plate and it seams that I cant get the squirt even hit it no matter how far I unscrew the timing screw. But I can make it hit vacuum release plate

:excuseme:

p.s. talking about 01 wr426 carb, the one without leak jet

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You have a different carb, you have a slant style, I believe and not a MX. I hope you kept careful track of exactly how much and what dirrection you turn the screw.

I suggest resetting the screw to OEM specs per your manual. If I am corrrect about you having a slant style, you need to do the Eddie mod as well as the taffy mod. The linkage slop as well as the excessive squirt volume are big problems.

If I am wrong about you having a slant style, I think you still need to reset the carb to OEM specs. Then adjust the AP by test riding. Turn in 1/2 turn increments, test, turn, test. As soon as the bog is gone during NORMAL riding you are done.

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Nah, it's FCR-MX, done O-ring and BK mods. Setting screw to oem specs doesn't help, cause even with screw removed, black plastic directly touching metal thing - no ap rod lash/freeplay, I cant make my ap squirt hit intake side of my slide. I whack the throttle - get big squirt from ap nozzle but no trace of fuel on the slide whatsoever :excuseme:

one question: does ap passage have any antidrainback valve on the squirter side? I know it has on the float bowl side but what about squirter side? My point is that that valve could be stuck open and when ap diaphragm goes up, sucking fuel from float bowl, it could also suck air from nozzle and nozzle side could be somewhat emptied...

any ideas?

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Glad to hear you have the MX, I was going to look at the fiche online to see for myself in a little while!

Do not get fixated on visually getting the squirt right, what matters is how it behaves when you ride. Set the AP timing back to OEM following the procedure in your manual EXACTLY. Typically this entails backing off on the idle speed knob until the slide is 100% down, then inserting a drill rod of a specific diameter to hold the slide at a certain point, then adjust the AP screw untill either there is just barely no play or a specified gap. Then ride the bike, turning the AP timing screw in 1/2 turn increments. Most of the time, CCW is what cures it.

No, the AP nozzle does not have a check valve. Think of the AP just like a childs squirt gun, for all intenets and purposes, it works exactly the same. The AP nozzle is so small compared to the fuel passages, the tiny bit of air it may draw back in it insignificant. If you get a strong squirt, the system is working correctly. Do not make the mistake many do and over analyze this.

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Okay, thanks alot, yep, the procedure is exactly what you said, will do that! I thing the bike is almost perfect already, o-ring mod made the biggest difference, not BK mod. first ride after mod, I'm on concrete, still used to that bog, twisted the throttle wfo, the bike screamed like a motorfcker, scaring shish out of me, I almost tipped over :excuseme:

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DID this mod as well as put in another diaphram with a shorter rivet in my crf 450 today.. All I can say is INSTANT ROOST:D

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I just did the o-ring mod. to my wifes 2005 WR250F, and also changed the leak jet from the stock 95 down to a 55. I'd say 50% of the off idle hesitation is gone but not all of it. I've tried adjusting the ap timing screw from all the way out in 1/8 turns in and it doesn't seem to make any noticeable difference. Do you think I need to go one more size smaller on leak jet? I see most people on here say they are using #40-45 leak jets?

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I Hope you kept very accurate notes about how much and in what direction you turned the screw from the OEM position. It is important to start at the factory setting and work from there. It never needs more than 2 full turns. If you did not keep good track, dig out your manual and reset it back according the exact procedure in the book.

Did you test by riding or was it on the stand?

Did you look to see if you have a good squirt?

What oring did you use?

You may need a smaller LJ, but lets wait a bit first.

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The beginning of this thread will answr a lot of questions. But...

The mod removes free play from the AP linkage, causing it to react quicker to throttle openings. The same result can be had (in a more permenant, albeit expensive) method by replacing the AP cam spring with a stiffer one, like the APS from Merge Racing.

Adjusting and modifying the AP is not always required. If you experience a bog during normal riding (not just reving the life out of your engine in your garage to impress you friends), then work to the AP is called for. However, you must first ensure your pilot jet is correct, the fuel screw is set right, you have the correct needle, the clip is set right and you have the right main jet.

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is this the correct way to do the mod?

this guy uses 2 o-rings in the vid

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It looks right however the resolution and size makes it hard to tell.

Two skinny orings is the same as a single large one. As long as they are relatively tight is what matters. The idea is that it removes the play from the linkage but allows some 'give' if the AP diaphragm stopper (the rivet) bottoms out.

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From just his description it doesnt sound right, but the second one was definitely correct...

He definitely describes each o-ring being installed a different way, odd...

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can anyone direct me to the link for FCR39mx proper tunning/adjustment technique ? I looked through FAQs but can't locate it. I recall someone mentioned it was in FAQs. thx

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can this or should this mod be done on an 2010 ktm 530 xcw??? havent seen that bike come up yet?

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if it has a fcr it can be done.. But does it need it is the real question, Does your bike bog?

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