spark plug question
 

I have a 2008 yami 250 4 stroke. After removing the plugs, I noticed one plug looked brand new.The other 5 showed normal wear. Any ideas ?

Re: spark plug question
 

Are they the same model plug w/ w/o gapping needed?

A non-firing plug( worse case scenario) would be filthy with gas and carbon all over the tip.

Are these plugs with adjustable prongs that gap must be set? Is so that was perfectly gapped.

The heat will make them a reddish brick like color. That's ok too.

Re: spark plug question
 

Thanks Frank, I will check the gap.Plug was clean, like it was never used.

Re: spark plug question
 

Have you taken a compression test on all cylinders??.. one very clean plug in an engine often indicates water intruding into that chamber.. It fires, and the combustion chamber, piston top, and plug get "steam cleaned" each combustion cycle.. You could have a small coolant leak into that cyl.. I would also get a small focused beam of light into each hole, or one of those tiny flexible lights sold at Autozone. If the chamber and top of piston are super clean as well, compared to the other cylinders, you might have water intrusion... Here's the problem.. often ,slight water intrusion into a chamber will not show up in a compression test, and the engine will run just fine.. Until of course, the piston gets scuffed, and the motor becomes instant junk...
Take the comp test, get a good look into all cyls, and don't be surprised if you have some water getting in... Typically its a bad head gasket... bob

Re: spark plug question
 

Thanks for the advise guys.