I have a 1979 CX 500 c. I am having a problem when I accelerate it sputters then when I give it full throttle it kicks in but sounds muffled. I checked the resistors in the cap and there was a little carbon fouling one side. I thought maybe the carbs so I tried putting some seafoam in to no avail. When sitting on the bike running I pull the right plug and it dies, when I pull the left plug it still runs . Anybody have any ideas?