Colder sparkplug on a bored engine?

[MarkSims]

I saw a post here recently by someone who had his engine bored. Thumper Racing recommended going to a one-step colder plug. I also noted that Kawasaki uses a 10 in the KX100 and a 9 in the KX85 - which are essentially the same except the bore.

So I started wondering if I should be using a 9 instead of the stock 8 in my KX310.

Can anyone enlighten me on why a bigger bore requires a colder plug and what a colder vs hotter plug does?

Thanks! Mark

 

[Rich Rohrich]

A change in the size of the bore has no specific influence on the spark plug heat range requirement.

 

[MarkSims]

Thanks Rich! I won't worry about it then.