From the research ive done on it, most will reccomend that you change your spark plugs after you run a tank of gas with seafoam in it, this is due to the carbon that it is suppose to get rid of will blacken up your plugs.
I run it first ride every season and also as a stabilizer in the summer.
I don't mix alot of it though. just enough to get the job done. Maybe 1/3 or less of a can in a full tank of 91 octane
Also, I have never changed out the plugs unless they need to be changed during normal riding conditions.
I swear by the stuff too. It's ran once a year in my Jeep, mower, tiller, snowblower, anything that is an internal combustion engine!
In my Jeep, I run half a can in the oil a couple hundred miles before the next oil change once or twice a year.
I like the stuff so much, I wrote them to try and be a dealer for it!
Just be sure to use this product as directed! POINT BLANK
Local machine/speed shop advised me to use Seafoam in my old truck engine for a month before I pulled it out for a rebuild. I used it in the fuel injection system as well as the oil. For a engine with bad rings that required a quart of oil every 3rd day, it was very easy to clean-up when I tore it apart.
Since then, I use it in every machine I own. Hands down, it is better than Sta-bil or any other stabilizer on the market. Hands down, it's the best add-in internal engine cleaner on the market.