426 Eating Spark Plugs !!!

Help my 02 426 keeps eating spark plugs, ive tried iridium plugs and they last less than an hour and standard NGK CR8E last about 3 hours, when i pull the plug it is generally carboned up and wet.

Well here's the most recent story:

I was entering a 3 hour enduro race, so the night before i put in a iridium plug all was fine i took it for a run on the road and still fine, i gets to the race venue the next morning and starts it 3 times in pits to make sure it would go and all was fine with first time kick every time, so i put the bike on the start line, then when told to do a 2 minute warm up it wouldn't go, so the race set off without me, i quickly replaced the plug with CR8E and off i go for just under 3 hours, all fine without a single beat missed, i gets home puts the bike away for a fortnight, then goes to kick it up and it fires once and then nothing, if i take out the plug it is dead no spark at all and if i put in a new plug fires up straight away!!

The above story has happened numerous times and now thinking about taking shares in NGK.

Any suggestion please.

Mark

1) Make sure you turn the gas off!

2) If you ever start the bike, DO NOT turn it off until it reaches full temp. Starting it and turning it off when it's only slightly warm will wet-foul the plug on my 426. If I always get it hot then one plug will go just about forever. This means NO starting it for 10 seconds in the pits to make sure it still starts. If you start it, get it hot before you turn it off!

3) If all else fails, try a different brand of gas.

I also had a similiar problem. My 2 outside intake valves where close to out of spec, and my center intake valve was very tight. I reshimmed the valves and all is well again. It hasn't fouled a plug since.

i would check your valve seals.when you turn it off oil seeps into the cylinder,thats what mine was doing.i would replace a plug and usually get 2 different riding practices in though.i still havent fixed it yet because i bought a new ktm but i make sure i bring the bike to TDC before i put her up,that way all valves are closed and no oil runs into the cylinder.yeah i knw thats being lazy but i have been working 7 days since the end of June,no time.

I've recently rebuilt the top end including valve seals, piston and reshimmed the valves leaving them a little loose.

Mark

Hi Marktt31

I had the same problem BIG TIME with My '02 right from new, I already own part of NGK due to this problem!

The cure for My bike was the BK mod ! When checking the duration of the accelerator pump My bike was at 3.6 seconds, after BK mod it is well under a second!

Have NOT fouled a plug since!!!!!!!!!!!!!

My 2000 426 had the same symptoms as your 02 did, but all i did to cure it was like sirthumpalot did. Also when you ride the bike fogg it as hard as you can and that helps to kkep the plug going strong in my unprofessional opinion... :applause:

By the way what do the iridium plugs perform like in comparison to the standard CR8E's :ride:

I had the same problem. About 50 kicks and it would finally run--replace the plug and it would start in one kick. Finally re--shimmed the valves andI am still on the same plug with no more fouling.

Hi Rebelex

The iridium plugs in my opinion do exactly the same as the standard cr8e's but i ride enduro racing not motox, so a few seconds here and there are not critical.

Mark

1) Make sure you turn the gas off!

2) If you ever start the bike, DO NOT turn it off until it reaches full temp. Starting it and turning it off when it's only slightly warm will wet-foul the plug on my 426. If I always get it hot then one plug will go just about forever. This means NO starting it for 10 seconds in the pits to make sure it still starts. If you start it, get it hot before you turn it off!

3) If all else fails, try a different brand of gas.

This is by far the cheapest solution to your spark plug eating thumper. I believe everyone with an YZ4.. something has had these problems. I cured my machine by following these steps. Re-shimming can be costly and time consuming.

What color is the plug? I am assuming that it is black (carbon fouled). Another consideration would be re-jetting. Just a thought.

Good luck.

This is by far the cheapest solution to your spark plug eating thumper. I believe everyone with an YZ4.. something has had these problems. I cured my machine by following these steps. Re-shimming can be costly and time consuming.

What color is the plug? I am assuming that it is black (carbon fouled). Another consideration would be re-jetting. Just a thought.

Good luck.

have you ever taken a plug check before a failure.

I had a problem like this as well.

- Re-evaluate your jetting. You are probably rich somewhere, most likely Pilot and/or needle. Im guessing you are getting black smoke when you gas it on the stand.

- Change brands of gas. Especially when they start running "Winter" mixes.

BK Mod and Proper Jetting. I would use a plug a week before this.

Now the bike starts and runs first or second kick every time with no worries. '02 YZ426F

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