YAMAHA > XJ 600 S - Can't figure what's happening

Hi

My name is Martah and my English is poor. Thanks all you guys for this forum.

I've a YAMAHA > XJ 600 S since 1992, the year I've bought it new. It´s a simple bike. Just fuel and oil. Some months ago start giving me an strange problem. Engine fails when accelerating, making the pum pum sound in the tailpipe just like if you accelerate and cut power (like in bike parties).

Well, after a lot of experiences i now know that using a spark plug NGK CR9EK instead of the correct spark, the CR8E or CR8EIX the bike works fine!!! The problem is in the right cylinder.

Doubts: Some one have any idea about this? Can the use oh CR9EK in the right cylinder be prejudicial to the bike?

Thanks in advance to you all

Marath  

Yamaha is one of the great brand in automobile industries and there are many beautiful Yamaha bikes that are easily available in the market.  
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