yz444 plug fouling (newbie)

4 replies to this topic
  • shaggy929rr

Posted June 01, 2008 - 04:48 AM


Hi to everyone i just joined the site today looks a brilliant site,and i,m hoping someone somewhere can help with the problem i,m having with my 02 yz426.
Firstly let me explain the background of the bike,i obtained the bike with engine in bits complete with worn out cams,piston/cylinder and big-end bearing and re-built fitting new con-rod kit,re-con cams,new timing chain,444cc big bore kit with piston and cast cylinder liner,filters ,oils and gaskets, all clearances and settings correct and double checked.After rebuild bike ran up well ,no smoke or mis-fires rev's cleanly with no unwanted noises or knocks temperature also fine,but has always been a pig to start i have read all the starting tecniques posts ,these help and i do usually get the bike going from cold after a lot of kicking and bruising to the bottom of my right foot,(god wish i had an electric starter) hot starts are usually easier.I have only been out on the bike a handful of times and every time i have experienced starting probs,sometimes having to bring the bike back home without even turning a wheel (most frustrating).I find when i remove the plug it's slightly blackened and usually slightly wet,it will run after cleaning/burning the plug off ,but the last few times i have had to change the plug for a new one,when done the bike starts and runs fine till the next time out when it gets harder to start with each stop ,it's getting to the point where once started i don't want to stop it for the rest of the day,and when running the bike runs absolutely perfect and is blindingly fast and powerful.I wonder if anyone cant supply some answers to help cure my problem,the bike has standard pipe,jets etc.I wonder would i benefit from any mods like the BK mod or the blue wire mod i have read about? do any plugs last longer or run better than others,does any body know of any jetting settings that work well with the big-bore kit?.I hope some can help as i really enjoy this bike when its working its a blast its just hard work to keep it reliable at the moment and is most frustrating.Many thanks for any suggestions.

  • grayracer513

Posted June 01, 2008 - 07:07 AM


It sounds like you are using too cold a plug. The bike needs a CR8-E (NGK) or equivalent. People will sometimes substitute colder plugs in the mistaken notion that that will keep the bike cooler. The only thing that gets cooler is the plug, which is too cold then to keep itself clean, and fouls.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • shaggy929rr

Posted June 01, 2008 - 09:39 AM


Hi, i have tried a cr9e plug in standard and platinum type with the same sort of reliability,i was of the understanding that a 10 grade plug was the standard for the bike? not sure though,i am going to try an NGK CR9EK plug next its a 9 grade plug with twin earths over the centre electrode in a hope that it will increase the spark or chance of sparking and maybe improve starting.

  • grayracer513

Posted June 01, 2008 - 10:01 AM


Again, the standard plug is a CR8-E

That's 2 full grades hotter than a 10. A 426 will foul 9's with no trouble at all. Put an 8 in it, and your problem should clear up.

  • shaggy929rr

Posted June 01, 2008 - 10:15 AM


ok will try an 8 and see how i go hope this sorts it thanks.

Related Content


James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.