yz444 plug fouling (newbie)

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.

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.

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.

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.

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

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