TOPIC:

Is there any prevailing wisdom on whether cold plugs (one range past factory spec) are called for if you ride mostly multi-hour highway trips? Not necessarily flat-out 75+ MPH all the time, but fast running without a lot of stopping. Assuming bike tuned and in stock configuration.

Or if the only way to be sure is to read the plugs, do I actually need to stop immediately at the end of a lengthy high-speed run to get a good reading? (Coast to a stop from full blast on a remote road somewhere..)

I do see some blackening when doing a read after idling, which itself could be a little smoother, but maybe this is just a price to pay for optimal running at higher throttle?

Thanks.

Plugs are designed to:

1. ignite air/fuel mixture
2. remove heat from area
3. clean combustion chamber

When using any heat range, you need to balance the function of #2 and #3 above. These functions pull in opposite directions. If you tend to remove MORE heat, you will get LESS cleaning and vise versa. If suffiently more heat is being generated by high speed operation and you use colder plugs to reduce operating temperatures, you will still have to clean the combustion chamber sufficiently where the valves/plugs don't soot up or foul.

One way of doing this is to ensure you are getting as good a spark for the most complete combustion possible. Check your voltage at your coils BEFORE changing heat ranges to ensure your coils are getting a full 12VDC because if they are not, then you will have a weaker spark than you should and you WILL start fouling plugs if you go to a colder plug to accomodate high speed operation.

Is there some issue when operating at higher speeds with the correct heat range? What brand and type plug do you currently use?

Read this:

www.ngksparkplugs.com/techinfo/spark_plu...nav=31000&country=US

The bike (KZ650) had and I've stayed with B8ES whereas it is listed for B7ES. I do ride mostly highway and some references including the NGK one above seem to suggest erring on the cold side is safer than hot due to preignition concerns. But I get occasional idle misses at low (1100-ish) RPMs and saw some minor blackening so thought maybe I should try hotter. I guess I should just try it and see what happens, huh?

12v to the coils means just that. It is the amount of current that the wire is able to pass (feed wire) that can be the reason the spark is weak. Dont let it fool you its whats inside. Little bitty wires are scary. BOO!