Spark Plugs

[Theflyingscot]

Just finished a quick service on the Vee.
Now this may be a daft question but I purchased CR8EIX plugs but the ones I have removed are CR9EX, after looking through the owners manual it states to fit the CR9's if the CR8's overheat.
How can you tell if your spark plugs are overheating?

[greywolf]

You are running a liquid cooled bike on the street. Stick to the 8s. Whoever put the 9s in was confounded by theory.

A plug that runs hot will exhibit faster electrode erosion.

[Theflyingscot]

Thanks for that, would the 9s contribute to poor running?

[greywolf]

Poor running could occur if the electrodes were worn.

[Theflyingscot]

They looked in okay condition, a little sooty though.

[hookie]

The higher the number, the cooler the plug will run I.e. it is less likely to over heat if the bike is driven very hard. Using a cooler plug (higher number e.g. 9 rather than 8) than the engine needs is more likely to foul as it doesn't run hot enough to be within it's design limits. I can't really see any situation where 9 grade plugs would need to be used a Vee except perhaps speed testing at Daytona! Even the TL1000 sport bikes only used 8 grade plugs.

If they a bit sooty, this could indicate that they're not getting hot enough. Hence the 8 grade plugs would be a better choice.

[greywolf]

Yeah, I got it backwards. 9s are cooler and will tend to develop deposits that could affect running.

[Theflyingscot]

That would explain it then, let's see how the proper plugs do.

[tallpaul]

I fitted CR8EIX plugs to my brothers vee. It runs perfectly well on them.

[hookie]

The CR8EIX Iridiums will be fine and should last 30,000+ miles. I've had a set in mine for over 20k and still going fine.