I have an early 80's 7.5 Evinrude. It was used as a rental motor in eastern Wash. at a resort so had had lots of daily use. I've also put a lot of use on it over the past 10 years with very little maintenance. It still starts easy, trolls like a dream but just seems like it only runs at about half speed at full throttle even though both plugs are firing. It is also smoking more. Any suggestions about whether to have it rebuilt ,or should I just unload it for cheap and look for another used motor? thanks in advance