I got a MM exhaust and mikuni. I been running it for a few months so I checked my plugs today to see if I was running rich or lean and one plug is black while the other looks light brown or tan (nice). Im running a 167.5 jet thinking about go down to a 165. What do you vets think about it?? its on a Prodrive with denso iridium plugs.

Keep it where it is. One cylinder will always run a little leaner then the other. I have the mikuni on mine and many other mods and also run the 167.5.. You could try a 165 but its better IMO to run it a little rich then lean. You dont want one side to be paper bag brown color and the other side almost white. I think where you have it should be fine

thanks much fowl. I my self prefer and feel safer running a lil bit rich then running lean.

You check plug color by warming up, installing new plugs, and running (no idle) for about 2 miles and then immediately kill it (pull kill switch- no idle). Then pull and check the ring at the base of the insulator.

Pulling them after you have run them and idled is not telling you anything.

DB8 is correct running a motor for a long time and pulling the plugs is not the proper way to read plugs. As he says warm it up. Throw a new set of plugs in run it full throttle for a couple miles kill it on plane with no idle, pull the plugs and read them. Take 6 - 8 plugs and different jets with you if you want to tune it to the optimum.

Russ

ok I will have to get some more plugs and I willl get back with yall.

Looking for this:

What determines if you need a colder or hotter plug. I'm running NGK cs6 plugs on a stock 35. Plugs have a little black but they are not all fouled up either.