My question is when jetting, can you tell the difference when reading the plug between:
1. Spot On
2. One size leaner than Spot On
3. One size richer than Spot On

The reason I ask is I'm jetting a Full Yoshi System on my Raptor with the airbox eliminator and 2 Uni Filters.

I started out with 155/160 Mikuni and it ran great. No white on the plug and the ring where the threads are was starting to turn light brown. The porcelain and the electrodes looked like new. I went to 167.5/172.5 and it felt a bit slower than the first try. I'm basing my comparison by the way it pulled and the ease of 3rd gear throttle wheelies. Next is 160/165 which will be later due to time constraints.

When reading articles about reading the plug, the pictures seem excessively lean or rich. I'm trying to figure out what they look like when I'm close. Is there going to be a difference and the only way to know is by performance?

Thanks,

 

ttt

 

go with how it rides the best

or get it dynoed

150-170 is what most have depending on elevation and air fliter setup

as long as the plug has some color to it and it isnt black you should be good

 

spark plug reading

 

ttt

 

Good article Burke. Here's another over fine tuning jetting.

Jetting Article

~HoundDog