Jump to content

The O-Ring Mod for an FCR

Recommended Posts

This is an easy job and does wonders for getting rid of the bog that many with an FCR-MX (Only, regular FCR's use the 'Taffy Mod') experience. It can be done with the carb on the bike.

I use a #78 O-Ring (7/16" O.D. X 1/4" I.D. X 3/32" thick) from the plumbing dept. of nearly any home improvement/hardware store. Cost is about $2.00 for a box of ten, share with your pals!

1) Remove the throttle wheel cover from your FCR.

2) Work the O-Ring over the timing adjustment screw.

FCRO-Ring1.jpg

FCRO-Ring2.jpg

3) Pull the O-Ring over the black AP cam thusly.

FCRO-Ring3.jpg

4) Re-install the throttle wheel cover. Just that simple!

Images courtesy of DouglasGraham, staff photographer

This post has been promoted to a wiki

  • Like 5

Share this post


Link to post
Share on other sites

Great write up William1. Helping the masses, as always. :prof:

I tip I found works for me to get the damn O-ring on with ham fists is to use a twist tie. I know because I first used some crappy ones that kept breaking and therefore have had lots of practice. It is especially helpful when putting the O-ring on while the carb is on the bike. Slide the twist tie through the O-ring and stretch the O-ring over the screw. If I used needle nose pliers like William1, I would always manage to drop the ring or nick it. Forgot sharing a 10 pack with friends it took that many to get a good one on. :bonk:

Also, isn't that O-ring mod mainly for the FCR MX?

Share this post


Link to post
Share on other sites
Great write up William1. Helping the masses, as always.

William - Great write up, good info. I was concerned about doing the o-ring mod prior to doing it, but it is easy. As easy as putting a sticker on the bike. :prof:

  • Like 1

Share this post


Link to post
Share on other sites
You need a good hand warshin'. :prof: So how's Doug's bike run?

We only went for a short ride, but he seemed pretty happy with it.

Eddie stocker motor with Hot Cams

Brand New TT FCR

Yosh Ti

Complete set Driven Racing sprockets and chain

We also replaced a bunch of fasteners with Stainless Steel button head Allens and greased the swing arm pivot. The two things that I were afraid of were dis-assembly of his Yosh RS, fortunately the mid pipe connection was not frozen, just stubborn and a frozen swingarm pivot, which only needed a little gentle tapping from a 6 pound hammer. One surprise was a stripped bolt hole but that was a non issue as we just Heli-Colied it. We started at 2PM on Friday, worked three hours, then started again on Saturday at 8 AM. Went for the madien ride at 5:30 PM. I am pretty pleased with how everything turned out. Baseline jetting we put in seems to be spot on or darn close. Will know better once Doug puts a few miles on it. He did have the water pump leak and has since resolved that.

Share this post


Link to post
Share on other sites

i had to use 2 o-rings on mine or was it three.i found that just one o-ring would eventually break.also when i did mine it also cut the ap duration by half.i went from 3 sec to 1.5 sec.you can still use the bk mod to get it down to 1 sec depending on the requirements of the motor

btw-nice write up,great pics,now evryone who uses the search function to find this will see it:thumbsup:

Share this post


Link to post
Share on other sites

BK mod AKA taffy mod is only for older style FCR's. You can use the timing screw if you are having an issue where the squirt is hitting the slide. 99.9% of the time, if it needs adjustment, it is loosened. This should be done in 1/8 turn increments, for a total of no more than 2 turns. My own bike responded well to a total of 3/8's of a turn. Less is more.

Share this post


Link to post
Share on other sites

the taffy mod is for the older style fcr.the bk mod is for the new fcrmx.this is a pic of my bk mod.i now use the o-ring mod.it works awsome.the bk mod got my squirt duration down from 3.5 sec to 1 sec.when i tuned the carb on the dyno i found that i didn't need the bk mod any more because i was going leaner on the main.

<a  href=img01350st.th.jpg' alt='img01350st.th.jp

Share this post


Link to post
Share on other sites

Great photography you must have hired a professional. You should post that photo of the new engine we did showing how to use the rear shock for more power.

Share this post


Link to post
Share on other sites

I have been told the '03 stock FCR carb on the E is different than most of the other FCR carbs out there. Which of these mods fit the '03 carb, O-ring or taffy? Does anyone have first hand experience with the JD Jetting accelerator pump modified diapraghm that eliminates bog?

Share this post


Link to post
Share on other sites

Taffy mod - If you carb is a slant style, it is a taffy mod model. also, if the AP rod is out side of the carb throttle wheel housing.

The BK mod is used to limit travel and is a rarely needed mod. Between the taffy mod, the O-Ring mod, timing screw adjustment and if possible, leak jet selection, all bog will be eliminated. FCR-MX's only need the O-ring and (rarely) the timing screw adjustment.

  • Like 1

Share this post


Link to post
Share on other sites

Sir William, when/how do you know you "need" the timing screw adjusted?

Rod

Share this post


Link to post
Share on other sites

Well, with the MX, if you have done the O-ring, have your carb jetted spot on or darn close, you experieince a bog during normal riding. This does not mean sitting still and nailing the throttle. Almost any engine can be made to bog at a stand still.

If, when looking at the slide, you twist the throttle and see the fuel hit the slide and go in the carb throat, you may neeed it to be adjusted to squirt a tad later.

But if you do not experience the bog, there is no need to adjust. Probably 20% of the carbs, do not need the O-ring. Probably 5% need the screw adjusted, at most.

Share this post


Link to post
Share on other sites

Yes, have the o ring, TT fcr. only a slight bog when shifting from 4th to 5th. It's not very noticeable. I believe the jetting is set correctly.

152 Main

45 pilot

EMR clip 4

2 turns out on fuel screw

sea level

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×