I have a 97 fomula III and the manual recomends br10es for a plug. When i bought it used 3 yrs ago it had br9es in it so that is what ive always ran. This seems to be one of the few sleds that are supposed to run the 10's. I had no problems the first 2 years but last trip I fouled 3 plugs in 500 miles. I have not sinc'd the carbs or even checked the oil setting yet but I was wondering if any body with a formula III runs the br10es and if any knows why this paticular sled is supposed to run a colder plug????