#1 spark plugs have carbon the rest are normal

The #1 spark plugs on both f225's have carbon buildup while the rest of the spark plugs are normal. The 2004 F225's with 700 hours on them run fine and have serviced the engines on schedule or well before. Shortly after changing the spark plugs I notice that the #1 cylinder spark plugs on both engines get carbon buildup while the rest of the spark plugs are normal. Your help is very much appreciated.

[robert graham]

Maybe the enrichening/starting/choke/prime start device is on that cylinder. My Yamaha 90HP has prime start on the middle cylinder and that plug is a bit blacker than the others. Maybe those cylinders are just running rich for some reason. If you have carbs rather than injectors, the main carb jets could be bigger in those cylinders. The jets are different on certain carbs on some of the larger multi-cylinder motors. If your motor runs very well, maybe just don't worry about it. Good Luck!

Had the Yamaha service tech hook the motors up to a computer today.

So far the data looks fine and within specs. Tech will forward and discus the data further with Yamaha. The temperature readings on each of the cylinders/plugs and thermostats was normal as well. Also checked the intakes/throttle bodies. Will see what they come up with.