Plug reading

Plug reading isn’t necessarily something I have a lot of experience with. Is this looking pretty good? …too lean?

EGT’s were good and actually went up a touch from 1060 to 1080 when I richness the mixture just a touch…bUT those weren’t back to back rubs and the temp dropped about 15 defeees between those runs.

Both sets of daya show EGT steadily climbing under acceleration showing no detonation.

Yamaha KT-100 with SR-Y pipe for reference.


Can’t actually read mixture from that picture. It might be a bit on the hot side though looking At the insulator core.

Also, consider running a fine wire racing plug like an NGK B9EGV or B9EIX, perhaps a 10 on hotter days.

Here’s some stuff on plugs:

Plug shown is an Autoloite AR51 which “everyone” runs in this engine. Looks like that is equivalent to an 8 heat range NGK

How many races are you running the thin wire plugs for?

In a KZ or FA I’d change them every weekend or every day. Not because I have to, but because I like to have a clean plug to read from.

If I’m not worried about reading the plug I’ll use them for a lonnnng time. The EIX are made from very durable metal so they don’t wear very fast at all. Even in the motors I have that would turn 19k+RPM.

There’s also the EV and EG which are cheaper to buy but don’t as long due to different metallurgy. Then again I’ve never worn one out perse either. If I have an ev or eg knocking around I’ll use it for practice. Save the EIX for racing.

Really I only change because I feel bad, or I’m looking to read the plug.

8 seems kinda hot to me for a piped KT. But it’ll stay clean on slow laps if that’s a concern.

I’ll caution you and say I’m not very well up on the specifics of the KT though.