Everyone with a 01 fouling plugs please read


The jetting is working great. I rode yesterday at 290 and had zero problems. I have not fouled a plug in two weeks and the bike is starting great.

I still want to try a CR7E plug. Just to see if it helps. Now that all the carbon has blown out I should not have any more problems.



01 YZ426F #85 Vet C

**FYI** I hope dealers and dealer supporters don't get upset here but you can get NGK CR8 sparkplugs at some of the automotive parts stores for half than what you normally pay. I paid $6.25 for one at my local bike shop and paid $3.19 ea. at Advanced Auto. They may have to order them but they get them the next day.


Are you having any luck solving your problem. I posted last night and have been reading the other post. My post matches yours exactly. 3 months no problem at all. Started with a dead spot when I whacked the throttle. Now it is so bad than when I whack the throttle it stalls. Won't come off of idle. It backfires all the time. All this without changing a thing. Have cleaned the carb, checked for leaks and tried a variety of jetting combinations. Nothing has worked. Hoping you have found the answer!!


I have my bike ready for the carb removal...and sometime this week I plan on switching jets, I also plan on checking my valves clearances (they probably wont need adjusting but better safe than sorry)! Also you said in a previous post that you had your fuel screw set at 1 1/2 turns out and you may need to adjust it? What did you decide works the best? Also do you have any tips for working on the 426's carb (since I havent taken it off yet)?

Also are you gonna ride this weekend? We are planning on riding Saturday (weather permitting)! Thanks,



I get my kicks on a 2001' YZ426!

Friendswood, TX


FYI, the idle mix ain’t an air screw, but you can call it whatever you want as long as you realize that in is leaner and out is richer (small screw on bottom of carb regulates fuel, not air).

Just checking bud…

If your bike really does like 2.75 turns out you may want to go with a richer pilot.


I'm at sea level 80 degress. I run 158 main, 42 pilot, 1.6 turns on fuel screw and third clip. My bike starts great and has not fouled a plug in over two weeks now. Throttle response is good also. It start idles right from the get go. I also, use the choke very sparingly.

Good Luck,



01 YZ426F #85 Vet C

I have tried all of these things and it still don't run right. Right now it is as good as it has been. The jetting is as follows:

1. Main = 168

2. Pilot = 45

3. Needel = 1 leaner

4. air screw = 2 3/4

I still get black soot in the exhaust, this is not right. All my friends have 2000's and they run fine.

I don't know what the deal is with these things but they are not working correctly. Even as good as you can get them they should run better.

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