Re: what is this rubber washer ? and why doesn't the ignition wire fit the plug ?
some kits come with a regular boot now. it's just poor quality control.
i replace the plug wire (it just unscrews from the CDI box) with a better quality, 7mm, copper core wire and a real boot from an auto parts store. i make my own and crimp the end on. it's pretty easy, it's better quality, and it allows you to make a longer plug wire so you can hide the CDI somewhere else (like under the motor.
the only thing the O-ring would be for is the carb. there's no other place for it. but it should be larger than the hole in the intake, and should fit snug into the carb. if it don't, someone musta just dropped it into the box.