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Discussion Starter · #1 ·
My sons 1999 400 ex is broken.Spark plug is melted,the bike let out some white smoke and started knocking and died. Now it wont even turn over.All the obvious stuff seemed to have been ok oil etc. But wow this plug is fried
 

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Will it turn over with the plug removed? My guess would be either the oil pump quit or it was running in a lean state. Was there any modifications done? Pipe Air filter Jet Kit?
 

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Yep if the plug is melted guess what the piston looks like, sounds like a LEAN condition.
 

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Yeah, I agree.
 

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Discussion Starter · #5 ·
nope no mods.valves were adjusted bout 20 hours ago but it ran fine i would think if valves were not adjusted properly you would notice right away
 

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Something went wrong somewhere.. Like I said you may have lost the oil pump?? Will it turn over with the plug removed?? but 9/10 if the plug is melted then there is a LEAN issue... does it have the stock air filter?
 

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Well I'm sad to say when you or who ever installed the Uni air filter they should have re-jetted the carb it has more air flow through the engine and therefore causing the bike to run excessivly lean, and over time it go to the point your at now. if you remover the side cap on the left side of the engine exposing the flywheel I think it's 17mm and turn it counter clockwise I think?? can you turn the engine over by hand? if you can I would say you may have gotten lucky pull the main jet out it shoul;d be a 148 bump it to a 150 that should richen it enough and turn the air screw in 1/2 turn and resset the idle that is if it can be salvaged.
 
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