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Spark Plug Choice

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I just recently purchased a brand new 2014 YZ85 for my son. My problem is that it keeps fouling up plugs. The bike came stock with an NGK BR10EG plug that didn't last but a half hour of riding. He has already gone through 3 of these plugs in about three hours of riding. I decided to go with a hotter plug NGK BR9ES which gave me better results but still only lasted a total of about 4 hours of riding. The local Yamaha dealer tells me my son is not riding the bike hard enough which may have been the case initially but I can say he rides the bike fairly hard and keeps the engine revving plenty high. I was considering going with an NGK Iridium plug because it apparently has more resistance to fouling. Will this help me or should I go with a an even hotter plug? Maybe a BR8?? but I fear damaging the engine if I go too hot. I am mixing the fuel according to manufacturer specs. (30:1) so this should not be a factor in my problem. Any advice??  

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You need to check your spark plug color (after puting in a new plug) after running it like he normally rides for a minute or so.  Like the other guy said, it's likely a jetting issue.  I'd also see what the guys who race are running as far as oil ratio.  30:1 seems a bit much if you are using a good oil, but see what the guys who race are using.  The manufacturer normally lists real rich mixtures to be on the safe side / compensate for people using medicocre oil.

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I would try running the iridium plug but I would stick with the #10 heat range as that is the one that yamaha recommends. As the other guys have said you are most likely running rich and will have to play with the jetting.

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You should rejet the bike.... Its not the plug...

^This^..

Plug fouling is 99% of the time a jetting issue. Most 2 strokes are jetted slightly (to very) rich from the factory in an attempt to compensate for any user errors in fuel quality, mix, etc.. Yes, if he could keep it pinned on the throttle stop all the time, it probably would be alright. But anything less and it's going to be too rich and foul plugs now and then.

Lot of jetting tutorials around the web, use them. Get your jetting right and it won't foul a plug no matter how the boy rides it. You see a lot of YZ85s used as tween aged kids' woods bikes around here, and they run all summer on the trails without fouling a plug. :thumbsup:

Edited by OLHILLBILLY

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"you're not riding it right" is the anthem of the totally incompetent. Stay away from those types and their advice. Far away. Jet the bike properly and you will NEVER foul another plug.

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Yhgeorge not true even if it's jetted right it can still foul a plug. He probably is barley giving it gas. Hop off

Edited by justin1478963

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Yhgeorge not true even if it's jetted right it can still foul a plug. He probably is barley giving it gas. Hop off

Sorry but no.

 

"Jetted Right"  Means that it is jetted appropriately based on atmospheric conditions, altitude, etc... AND the type of riding/ rider skill and habits.  I can be at the same altitude and temperature and if I am doing very technical rock crawling type of riding I would jet differently than if I was doing wide open sand riding.  If you foul a plug, than the jetting was not correct for those conditions and that rider.

Edited by c-slak

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Sorry but no.

"Jetted Right" Means that it is jetted appropriately based on atmospheric conditions, altitude, etc... AND the type of riding. I can be at the same altitude and temperature and if I am doing very technical rock crawling type of riding I would jet differently than if I was doing wide open sand riding. If you foul a plug, than the jetting was not correct for those conditions and that rider.

I'm glad everyone on here is an expert. So your saying when jetted correctly it's impossible to foul one?

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I'm glad everyone on here is an expert. So your saying when jetted correctly it's impossible to foul one?

Mechanical issues such as weak spark, low compression etc could cause plug fouling.  An extremely old spark plug could also be at fault.  If you read his initial post it is a brand new bike with multiple new spark plugs.  This rules out the likelihood of those other possibilities. 

 

Sorry but as stated previously, "Rev it harder" is terrible advice. 

Edited by c-slak

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Mechanical issues such as weak spark, low compression etc could cause plug fouling. An extremely old spark plug could also be at fault. If you read his initial post it is a brand new bike with multiple new spark plugs. This rules out the likelihood of those other possibilities.

Sorry but as stated previously, "Rev it harder" is terrible advice.

I bet money it's not being ridden like a 2 stroke should and that's why it's fouling plugs.

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Funk you monk. Read the post were he says himself that his son was not riding it correctly. How old is he 10-12 first bike? First 2 stroke? If u put around the yard it will foul over and over again

&%$#@! you monk. Read the post were he says himself that his son was not riding it correctly. How old is he 10-12 first bike? First 2 stroke? If u put around the yard it will foul over and over again

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Funk you monk. Read the post were he says himself that his son was not riding it correctly. How old is he 10-12 first bike? First 2 stroke? If u put around the yard it will foul over and over again the dealer is right or take the dawn bike back for one that doesn't foul plugs like that. Even if it wasn't jetted spot on if rode right it wouldn't foul like that

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I bet money it's not being ridden like a 2 stroke should and that's why it's fouling plugs.

Please educate us all on how a 2 stroke is meant to be ridden?

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Please educate us all on how a 2 stroke is meant to be ridden?

simple don't lug it around like a ttr125. I bet I'd get on that dawn 85 and ride all day long

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