I need some advice. I have the p/n:4272 on a yamaha super jet. It appears that I have spark with no load and that is by grounding the plugs and turning over the motor. It idles fine when running, but bogs when you rev it up. One spark plug looks like it's new and wet looking as if there is no spark. (started with fresh plugs). It seems to me that there is a lack of spark when it's under load. Can this occur? What can i do to test it if possible?

Thanks in advance,