Reading spark plugs, plug chop

Hey Guys,

I have a 1983 KZ440 LTD with pods and a short glass pack exhaust. I am trying to do my plug chops and dial it in. It runs great, just trying to dial it in. I installed a sigma6 jet kit when I put it together last year. Here is my problem, i've gotten myself confused with the color of my plugs. I've been chasing the light tan porcelain that I thought I should be looking for. so I kept going up in jet size. I'm at a 130 and still no color on the porcelain. I do however get a black ring around the base of the threads. I was doing some web searching and some sights suggest not to look at the porcelain at all for jetting. That the ring around the threads is what you should be looking at. So if that's the case I have been rich for some time now and need to go back down in size. But here's where I get confused, now I never ride at WOT (except during my plug chop) so the main jet never relly comes in to play during my rides, but either I'm getting more comfortable on it (took it real easy last year) or the bike is more responsive with a larger main... seems to get to 70 without working, where as I remember last year it being work to get to 60... Any insight would be greatly appreciated.

Take a look at the link below. Even though it isn't great, it does have some info that should help. Ed

www.wallaceracing.com/plug-reading-lm.html

That is one of the sights I stumbled across while doing my research. So now what confuses me is I guess I am rich, but why does it feel better?

There is more than one thing at play here. First, as you mention, you are seldom on the main only. However, the needle setting is directly related to the size of the main (think about it). A larger main will have a direct effect on the needle because the needle is allowing more fuel to insert itself into the air stream when it lifts out of a larger diameter hole. It also has a secondary benefit of cooling down the combustion chamber to prevent pre-detonation, known as knock or ping. A black ring is O.K. as long as you are not fouling plugs.

Right, I knew running it on the rich side was good for keeping it cool. Maybe I'll do a plug chop at 1/2 to 3/4 to see if the needle is about right. It feels real good all over, so I'm not worried about getting it to "run better" I just want to be able to say It's jetted right.

The main jet comes into play anytime the slide is lifted off idle position. The main jet is still a restriction, even though the needle makes up most of the fuel restriction at lower throttle positions.

You can mask needle position error by compensating with the main jet.

The problem with reading plugs is that it becomes increasingly difficult to tell what is going on as your jetting gets closer to what it should be. Once your main and needle are close, plug chops become less effective since it will take much longer for the color to change when you are close to correct on the jetting. It also gets increasingly difficult to tell whether what you are seeing is due to full-throttle, or part throttle operation.

You will have to start doing bracket testing. That is go in one direction until it does not run right, then go in the other direction until it does not run right, then choose a point near the middle.

Opening the throttle under load is when it will be at its richest, and cruising steady at constant throttle will be when its at its leanest while throttle is open. (It will actually get leaner if you close the throttle, which can lead to popping if it is way too lean.)