Please see the pic in the link below. There are two spark plugs both out of DS’s. One from mine and one from my brother in-laws.

Both quads have the almost the same mods:
JE 11.5:1 piston
ported intake
Suppertrap end cap (12 discs)
K&N air filter
DR9EA plugs / one step colder than stock (Heat range looks to hot also)

The only difference is jetting (Mine 180 mikuni main/needle 3rd clip, Brother in-law 172.5 Mikuni main/needle 4th clip) and My brother in-laws DS has a Ron woods CDI, and Pro com Rectifier.

The Strange thing is the darker plug came out of my brother in-laws quad and the lighter out of mine. Why is that, wouldn’t the larger main jet make it richer?

Sparkplug

Thanks

 

Could be a zillion things from cam timing to total compression, to differences in the intake or exhaust tract, head, or even valve grind.
Just for kicks I would do a compression on both quads when they are stone cold and see what you come up with.
Even a small amout of float level can change the fuel rate.
Even people that build engines 24/day can't explain why some engines have a slightly higher BSFC rate.

 

Could also be as simple as what RPM you pulled the plugs out at. If it was WOT the main jet would be the difference. It it was mid range, the needle position would do it.

 

What about the heat range?