I have a problem with this sled. It has been blackening the spark plugs and basically has poor preformance. Poor bottom end etc. Wondering if it is jetting or oil. When starting it cold it runs really ruff. Even after completely warming it up and taking off it sound like it's flouding itself. Smokes like crazy too. This has been going on now for quite some time. Took it in to a shop last year and was told that the carbs were froze up. Paid 150 bucks and still runs like crap. Any suggestions.