Plug fouling? Yamaha parts manual shows wrong spark plug

Beware when buying spare plugs, as the dealer may sell you too cold a heat range--which will lead to plug fouling. The dealer parts manaul lists a CR9E for the '01 426. However, my bike was delivered with a CR8E and the service/owners manual also lists a CR8E as the correct plug.

If you run a "9" heat range plug, it will definately foul faster than the proper "8" series. In fact, woods riders and others that aren't riding at continous WFO, can probably get by running a CR7E.

This is because--like all manufacturers-- Yamaha is going to play it safe and install a plug cold enough to prevent preignition even when ridden in the deepest, fastest sandwash possible. Slow speed riders don't need that huge safety margin.

I have a 01' 426 and probably have 50-60 hrs on it! I had a CR8E plug in it from the factory! And one day the "8" fouled out due to the cold weather and had to clean it! Now I have a CR9E which fouled today (I live in the Houston, TX area and it was 35-40 degrees when it fouled) This is what happened: When I got to the track it wanted to start about 5 times and then it wouldn't fire at all! So I had to take the CR9E plug out and replace it with my old CR8E and it started the first 3 kicks, and ran fine all day! Is this normal??? It seems like both the plugs that fouled out happened in the same circumstances (right after the trailer ride to the track)! Have yall had this problem... I know jaybird67k lives fairly close to me and doesnt have a problem! I think my pilot screw needs to be fine tuned! The problem is i cant find my pilot screw...where is it at? Yamaha sure crammed the engine in the frame! I really would appreciate your comments it sucks having to pull the tank every time I ride! I really appreciate it!


Garrett Berg


I get my kicks on a 2001' YZ426!

Friendswood, TX

have you guys tried putting the racing plugs with the needle point in your bikes o tried on of those bosch 4+ plugs.

The pilot screw is on the bottom of the float bowl in the deep recessed hole. It takes a VERY small/short screw driver. This is a FUEL screw, turning it out will richen.

Originally posted by vznx1w:

The dealer parts manaul lists a CR9E for the '01 426.

The parts fiche for the ’00 lists both, and although the 8 is marked “STD,” I guess not all parts guys notice this because I was sold a 9 as well. I also fouled it and only run the 8 now.

I think scottzx7rr can get you some CR7Es real cheap… :)

[This message has been edited by Hick (edited 12-18-2000).]


thanks for the info...i found the fuel screw (finally...that sucker is packed in there) What do you guys jet you 426's to at sea level (mine runs great except when i try to start it after the trailer ride on a cold day) so is it the fuel screw? I read in a recent MXA mag that you will have to turn the fuel screw out some as it gets colder?? But isnt that why i foul plugs because of too much fuel? Thanks



I get my kicks on a 2001' YZ426!

Friendswood, TX

[This message has been edited by motoman393 (edited 12-18-2000).]

I’m sure you realize this but if you’re pet cock is on during the trailer ride you may be trying to start an already flooded bike.

I’m hearing so much about fouling plugs on cold YZFs that I wonder if it isn’t just another four stroke learning curve thing. Let the bike idle (on its own) for a minute before you ride it. The few times I’ve seen YZFs foul plugs is when they are ridden before being properly warmed up, that’s how I fouled a CR9E on my 426…

Hope this helps.

i have been riding 4 strokes for 3+ yrs. The gas was off when i transported it! I generally wait about 2-3 mins before i go ride. What happened was i tried to start it and it started about 5 times but only ran for about 2 secs then died (the choke was on) then after that it would not start at all (i didnt even touch the gas) so i had to put in my old plug! Just out of curiousity what plug would yall recommend the 8 or 9? And what is the difference! Thanks,



I get my kicks on a 2001' YZ426!

Friendswood, TX

Originally posted by motoman393:

i have been riding 4 strokes for 3+ yrs. The gas was off when i transported it!


Yeah, I didn’t mean to insult your Dirt Bike IQ, just thought I’d cover all the bases. How many thumpers with an accelerator pump have you owned? I always suspect a happy wrist when someone fouls a plug. Also, although this has never happened to me, the check valve on the gas tank breather can allow pressure to build up in the tank (picture the gas sloshing as you transport), forcing fuel past needle valve and into motor. Try it w/out the check.

I’ve used one NGK CR9 which I fouled but I didn’t warm the bike up. Since then I’ve become a better thumper rider and have run the 8 exclusively and have fouled no plugs. NGKs get hotter on lower numbers so either the 9 is too cold or I should’ve warmed up the bike better.

You see a lot of “hard to start” questions here, I always recommend some experimentation preceded and followed by a good “clearing” of the motor. I’ll define that as 5 good, swift kicks w/ no throttle, no choke, compression release engaged and hot start pulled. Limit your experimental kicks to five also, if she doesn’t fire clear it and try something else.

I always turn up the idle one turn when my 426 is cold, this helps in starting and allows it to idle unattended while I put on my helmet and such, by then it will be pretty warmed up. I (almost) never use the choke but it rarely freezes here in the dez, I just richen it up with about a second’s worth of acc. pump (twist to about ¼ and hold for one second).

Maybe you are loading it up during your start and warm-up routine. On the other hand we’ve already heard of a few guys where some flaw in the ’01 carb is causing excessive plug fouling.

I predict as you get to know the bike this will quit happening to you.

Thanks for the info Hick i apprecaite it! I have tried all the suggestions except the fuel breather hose (that hose works awesome for bleeding your brakes since it is a one way valve and it came on the bike so it was free...well sort of lol) I think i will stick with a CR8E plug! I have heard guys say if you oil your filter before you ride it wont start and both times i have fouled out it was the day after i oiled the filter...but i let it sit for 24hrs (weird) oh well! This is my 2nd 4 stroke with an accelerator pump just takes time to get used to :)! Thanks a bunch!

Garrett Berg


I get my kicks on a 2001' YZ426!

Friendswood, TX

Thanks Hick. LOL


Scott #431

Some Fear Racing "Cause if you don't have any you ain't going fast enough"

'99 YZ400F(Coming to a Theater near you soon)

'92 ZX-7R and '97 ZX-7RR

"Doesn't hurt till the bone is exposed"

"When cut do you bleed green? I do!"


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