Hi I have a 2005 Ski Doo SDI 600 it has been backfiring a lot. I always hear people say the sdi's are known to do this. I am running br8ecs plugs and the plugs are definitely fouled, should I change to br9ecs plugs? I've checked in take boots they look fine no cracks. The sled idles fine but when you are on the gas and let off it backfires like its loading its self up, I would appreciate any help I could get.