I have an OS 18 and its been doin great. But now its burning out plugs. Not just every once in awhile, I can't even get through one tank of gas!!! I tried a few diff things- types of plugs, richer settings, leaner settings and still nothin. The only thing that cam close to helping was the rich setting but it ran like crap. Any body have any probs like this before??? If so whats goin on? And how do I fix it?