Found out why plugs are always fouling!!!!

Maybe you should bring that up with the Yamaha Factories and they could fix that problem for you. Maybe make the bike less appealing to little kids or something!! tongue.gif



"What's that?"

"It's a Yellow 99' YZ400!!"

[This message has been edited by sirhk (edited October 08, 2001).]

Or you could just turn off your gas????????


If life is not a blur. You aren't going fast enough

Fourstroker, There has been alot of talk in the past about fowling plugs, I'm still on my genuine one with nearly 3,800 Kms, I was in a dealer the other day and the guy told me that Yamaha has come good and admitted that there is a fix for the fowling plug syndrome, apparently the fix is in the TPS (throttle position sensor). Two bikes from the factory

yet one will fowl plugs and one won't.

The dealer told me that it would be a free fix due to Yamaha admitting that some of the factory set TPS's were incorrect.


don't just leave us hanging, tell us more.

can anyone else find anything out?


And what was the source of your info?

I'd love to get this fixed!

Turn your fuel off....Run the bike until the fuel in the carb runs dry...then put blue to bed...Twist all they want and the plug won't foul....You can also place a clear fuel filter between the tank and the carb to ensure the line is actually dry....

Bonzai grin.gif

Taffy & JD When I went into the dealer I asked for a plug for my WR, as I lent my spare to a guy who had fowled his on a ride the previous weekend,(before we even started) as soon as I mentioned spark plug, he was straight onto me about Yamaha denying there was a problem, and told

me that Yamaha Australia had informed them after many complaints that "YES" there was a

TPS problem, from factory setting. Now I

stand to be corrected, The dealer I spoke to said that they would do for FREE any bike that they had sold, otherwise it was about an hours worth of work to fix it, it was on the lines of setting the TPS to the lowest setting then holding the bike @1800 revs and adjusting the pump aswell, he didn't go much further than that, and assured me that was the fix. As I havn't fowled one plug I wasn't all that interested. I'd read many posts on this site about fowled plugs but it was an issue to me that had never occured and I was under the impression you guys had it sorted out with jetting etc.

I could possibly find out more or give you the dealers details in an E-mail.



My wife finally confessed and told me that my twin sons (11 year olds) come home from school everyday with their buddies and take turns sitting on my thumper and twist the throttle 100's of times each. I guess this would be causing all of my plug problems lately huh? My wife said she didn't think they could hurt the bike and they all looked so cute playing on it (just keeps them out of her hair I guess).

I will hang all of them up tonight in the basement by their thumbs!! I will use my wife's favorite cotton blouse to wash off my thumper this evening also, I'll tell her it works so nice.

I finally found the culprits (HOORAY)!


Same exact thing happend to us. we had a bunch of reletives over, none who rode, all who were interested in the bikes. Low and behold, walk into the garage, about 7 young children clustered around the bikes, turning, prodding, twisting. they spent so much time twisting the throttle on my 250 that there was literally fuel sitting in the bottom of the cylinder (thanks also the the fact that the 13 year old kid was trying to kick it over). And get this, one of the little kids was playing with the tailight on our quad (which comes of to reveal a little medkit/plug storage area) undid the latch and yanked on it so hard that the wires ripped out of the light, had to get a new one from Honda. This is somewhat forgiveable, there kids (youngest was 5, oldest was 13). But the thing that got me, was that the mom of the little kid saw him do it and was trying to put it back on so we wouldnt notice. Grrrreat, I was real happy with her.

Anyway, the moral of the story is that we spend muchos dinero on our fun machines, keep an eye on them.

[This message has been edited by eater_of_dirt (edited October 09, 2001).]

Drag the little rodents behind the quad for a few hundred yards! That'll fix 'em. On second thought....drag the MOM. It's like punishing the owners of the biting dog. The dog doesn't know any better than what the owners taught 'em!


Y2K WR400FM,Answer top tree w/Accu-Trax clamp,Pro-Tapers(CR-Hi w/ EE handguards),Devol Rad. & frame guards, Guts tall soft foam w/ ballistic cover, 14/52 w/DID VM X-Ring, Kouba-T,Michelin M-12's ft.& rr.,12 oz. flywheel weight, Zip-Ty Racing Link & Shark Fin(plus everythhing else cool that Ty offers), Cycra front rotor guard and T.M. Designworks Chain guide, buffer & chain wheels. Street legal except for the non-"DOT" tires.


Thanks for the tip. The TPS is easy enough that most "electrically" inclined could do it or at least check it. The pump adjustment is interesting, I wonder how many turns in from the "touch point" that would be.

Or take, hold the comp. release in, and kick it HARD 10 times. See if it starts then.

IF not....repeat, only hold throttle WIDE OPEN. Comp. Release in, throttle WIDE open, and KICK LIKE HECK until she fires. She will.....just be ready to release that comp. lever, and back off the gas FAST.


'01 KTM 520 SX

'95 KX 250 FOR SALE!!! -asking $2000 with decent amount of plastics/decals, parts!!

AMA Dist 6 Member

Hare Scramble Class B #523

James D,

I'll make a phone call and try to find out for you.??????


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