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As you probably know, there are quite a few reasons for dirty exhaust tips. Some of the suggestions here are simple. If they turn out to not indicate why your having the issue, pull a couple of plugs and take a compression check (all of them would be best (meaning at least one per cylinder). Cleaning the top end with a quart of good kerosene in a full tank wouldn't hurt, as well as a flush of the oil with at least a 1 1/2 quart kerosene before an oil change (careful you don't trip/stick your oil level sensor). Kerosene is the major ingredient in fuel system cleaners and engine flush products. It shouldn't harm any components along either the top or bottom end. Used IAW those products designed for periodic maintenance, it will not do any damage. Remember, the ratio is for a full system (top or bottom, as in oil or gas). The grade of kerosene isn't that important because it is either flushed or burned quickly. Just don't overdo it (we all know excessive good things isn't a good thing).


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