Proper spark plug

cturek

XS400 Addict
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I have been running NGK BP7ES's in my 400 per the Haynes manual which, in the ignition chapter, says that all XS400's run BP7ES. However, I'm looking thru the Yamaha Service Manual and I just read that the Standard plug is BP6ES. (It also lists the BP5ES for "Hot" and BP7ES for "Cold").

Now I'm confused. Should I be running the hotter BP6ES? Most of my riding is local, not highway riding. What plugs do you guys run?
 
I have been running NGK BP7ES's in my 400 per the Haynes manual which, in the ignition chapter, says that all XS400's run BP7ES. However, I'm looking thru the Yamaha Service Manual and I just read that the Standard plug is BP6ES. (It also lists the BP5ES for "Hot" and BP7ES for "Cold").

Now I'm confused. Should I be running the hotter BP6ES? Most of my riding is local, not highway riding. What plugs do you guys run?
I actually run an 8 in mine, although I never really noticed any difference at all. I know that running a hotter plug can cover up symptoms of other problems inside the engine, so be careful when changing to a hotter plug. When using a hotter plug, overheating can rise from pre-ignition. I just chose to runner a colder plug in mine since I have straight exhaust and pod filters. I will probably switch back to a 7 the next time I change plugs though. Spark plugs are cheap enough that you could just buy two of a couple different heat ranges and just do a plug chop on each set and see what the plugs look like.
 
Different heat ranges for different climates and jetting. Always run the coldest plug tht doen't foul. It hasnothing to do with the amount of spark it is just how hot in degreees the tip gets. As Hardtailed77 says you don't want pre-ignition.
 
i have been running ngk bpr7eix iridium plugs for about 5 years now and my bike rums a lot better than when i used the standard ones. if you buy them from yamaha they are 20$ each. if you go to a napa store they are 9 each. mikesxs also sells them for the same price.
 
The shape of the ceramic insulator is the difference between "hot" and "cold" plugs.The hot keeps the heat at the tip longer and the cold allows the heat to be dissipated more quickly.Hot plugs are better for short trips or heavy duty use.The cold plugs are suited for highway use.Gentleman Jim is right in that it's best to use the coldest plug that don't foul. lha
 
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