hi guys after looking at the pic,s of plugs i would say that the right side carb is very rich but the left side carb is running extremely lean to the point of fuel starvation. the ground strap is showing signs of discoloration from high heat and the porcelin insulator is clean. not as clean as we would see on a race engin after a clean cut but those plugs tell me to look at the float levels in both carbs.
it looks like the float is to low or there is trash in the needle and seat or trash in the high speed jet of the left carb.
i would also check the float leval on the right carb. hope this helps