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2coldnpagosa

Spark Plug Getting Fried?

10 posts in this topic

Ok, I have a weird problem that I have never faced before.

My Yz400 used to run great, but for some reason it has been frieng plugs like mad, 2 plugs per ride. (8 hours)

I ran through my electrical and the coils are at the correct omage, but for some reason my plugs are getting fried, not fouling them though.

someone plz help me, i have a race in a week and i cant afford to take it to my local shop, they have ripped me off $600 before.

thanks for the input...

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Sorry to hear you have this problem. My brother once had a CR250 that would fry a plug every 2 hours or so. Plug would simply quit sparking and no amount of drying out fuel foul or anything else we ever did would cure this with the exception of installing a new plug. hjope you figure it out.

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I am no expert, but my guess would have to be excessive cylinder temp. I highly doubt the ignition system (coil and capacitors) would allow excessive amperage burning up the plug. I would richen up the A/F, or try a colder plug. Like I say its only my guess.

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ok, by fried i mean that it wont spark at all, and its not wet it just stops working, i have no idea what to do... could it be the cdi unit?

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Take a fried plug and run a continuity test on it. It could have somehow melted internally from a too lean condition as implied earlier. If it is that lean, cylinder damage is next.

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ok, by fried i mean that it wont spark at all, and its not wet it just stops working, i have no idea what to do... could it be the cdi unit?

Okay...I can't offer any advice at this point other than I am experience the EXACT same damn thing!

I rode last night and the bike would not start so I installed a brand spankin new CR8E and the bike fired first kick. The bike ran like a badass for about 45 minutes and then slowly started running worse and worse. I pulled the plug and it was kinda sooty, but not bad. I wire brushed the plug and it looked nearly brand new again. Installed the plug...the bike would not start. I grabbed another new plug and plugged it into the spark boot and cycled the kick start looking for spark...I saw NONE. I put the plug back into the bike anyway...it fired FIRST KICK! The bike ran like a top for another hour and then started slowly detiorating.

I can only think that the coil is going bad, because during the first 45 minutes the jetting seems SPOT ON. :excuseme:

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Okay...I can't offer any advice at this point other than I am experience the EXACT same damn thing!

I rode last night and the bike would not start so I installed a brand spankin new CR8E and the bike fired first kick. The bike ran like a badass for about 45 minutes and then slowly started running worse and worse. I pulled the plug and it was kinda sooty, but not bad. I wire brushed the plug and it looked nearly brand new again. Installed the plug...the bike would not start. I grabbed another new plug and plugged it into the spark boot and cycled the kick start looking for spark...I saw NONE. I put the plug back into the bike anyway...it fired FIRST KICK! The bike ran like a top for another hour and then started slowly detiorating.

I can only think that the coil is going bad, because during the first 45 minutes the jetting seems SPOT ON. :excuseme:

You know when I first got my 426 it would foul/fry a plug and would never start with that plug again no matter how well you cleaned it. I changed a few things that eliminated the condition such as the BK mod and changed my coil to a cap/coil combo from a Hayabusa and never had the problem again. I never thought that the plug could have burnt out but that is what you are describing. I wouldnt think any kind of spike would have harmed a plug,but maybe it can. I never checked continuity on a plug after it failed but was always curious as to why it would never restart with the used plug, I brushed them, filed them, gapped them, chemically cleaned them and no matter what they would never start again til I put a brand new plug in. Maybe it was just the coil after all. I thought the no coil on the frame looked better so I rigged the cap from a Hayabusa just like Tim Ferry had on his bike, though his cap/coil was probably from a R1 :bonk: Have you tried to measure continuity or resistance on a bad plug? Compare it to a new plug and let us know.

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That is a really great idea. I am going after the coil tonight and will measure the spark plug resistance too. Since these are Resistor type plugs, does that mean that there is a resistor in them that could break down?

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I really dont know. It just seemed like the first place to start. The spark is still getting to the plug it just isnt going thru it. When I was having the problem I never even thought the plug could be physically damaged. If there is a difference in the plugs after they are fried/fouled, I would write/email the manufacturers and ask what might cause that problem. I would have thought somebody on TT might have some more info but hey havent chimed in yet. I would think a plug could stand extreme temperature and electrical changes with no damage.

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