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Carb Adjustment What a Blast!!

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I checked the plug because from 1/2 to Full throttle it seems to spit and

sputter a little as well as flatten out on the performance.

It looked like it had been in my chimney there was nothing white about it or even

tan for that matter. I cleaned it up a bit and put it back in for now.

Anyone now a cheap place to buy plugs on the web?

I have the carb out now to perform the throttle stop Mod.

I'm hoping this will lean things up a little?!?!?

I checked with the way the stop was adjusted the slide thingy

was only going 1/2 way up. I cut the screw down to 21 mm which

allowed the slide to open "all the way" but not past the throttle

body wall. I didn't want to freak out the TPS by going too far

Assuming with this mod the slide going all the way up will give much

more air and lean the fuel mix out???

Other things I can do while i have the carb out?

I don't have any other jet's but the extra ones that came with the bike.

So I replaced the 165 MainJet with a 160.

I did notice the squirt lasts about 1 1/2 seconds

this doesn't looks to be a fun mod !!

Well I couldn't wait I put the carb back in and took it for a test.

ALL I CAN SAY IS "Holy Sh**" It jest keeps pulling. I'm going to have to

learn how to drive it all over again. What was Yamaha thinking by detuning

a bike so much? It is "Mad Fast" :) If all the other mods like YZ timing

give the bike that much of a boost It just MIGHT BE too fast for me :D

I would bet though the rest of the carb circuit is still running rich.

A little worried to do the rest of the carb tuning though cause there's so much more to it

than just changing a jet out.

I have an 02 wr426 with stock pipe but ALL baffling pulled out, Lid off the air box,

and gray wire snipped. Now with Throttle Stop

and Main Jet swap.

Opinions Please??

Thanks guys


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Yeah, the carb has a main jet, pilot jet, starter jet, leak jet, main air jet, pilot air jet, fuel screw, accelerator pump, air cut valve, throttle cut out, and a needle that has over 200 shapes available. And you can Taffy mod it, BK mod it, put a P38 on it, stop up air cut valve, remove various diaphrams. It all gets imponderable at times.

Sound like you're new to the FCR carb. Might try 'Jetting 101' over on the 250F forum. Use the search key, its never in the 2 week group. After that introductory class, you can try the "Jetting Q's" topic on this forum. You seem to already have found the key to some more performance but unless you are lucky there's much more to get.

Good luck,


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Mark -

Actually I was reading the 'Jetting 101'

last nite in bed :)

Actually I was reading it and the manual while doing these mods today.

Much appreciation to the compilation of that article too.

I did notice after the MainJet change today that

when sitting idling and giving a quick twist there

is split second delay like the engine dies and then revs up? Is this what's considered the bog.

And I should've changed out the Pilot Jet as well??

Course then I'm guessing that would change the JetNeedle and would have to change the clip settings?

Once you change one thing in the carb it affects other parts of the carb?

Thanks :D

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I did a search for the Jetting Q's Topic and came up dry?!?!?

I wonder about the database here sometimes?

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Try the search without the apostrophy "jetting qs"

I wonder about the members here sometimes :D:):D:D

Bill :D

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I wonder about myself, sometimes! L.O.L. :)

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See that's why we need good moderators around here. :D

Thanks Bill it's amazing what an apostrophe can do to ya.

Took it out and found what I was looking for 144 pages printed out I be up all nite reading that :D

ON the Jetting issue though I think just the throttle stop and the going from 165 to 160 in the main jet has really leaned up the whole circuit. I even get a backfire through the muffler when I kill the bike now ?!?!?

It worries me as the thought of backfiring through the carb and setting my UNINSURED bike ablaze would not be good :)

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