A couple of weeks ago, I bought a 1977 14ft Cruise Craft Rogue with a 1971 Evinrude 70 hp, both in very good apparent condition - as was the trailer. All suggested a sense of 'well looked after' especially when the original, almost unmarked, two-tone grey trim still carries the embossed Cruise Craft logos.
Trailered it home and took it out for a serious test. Over 50 kph and WOT about 5200. Started well and ran well, and sounded good. Ran hither and thither for about two hours. Discovered the hour meter - 665 hours - a. worked and b. was accurate. So far so good.
Next trip the engine refused to trim down from tilt as we prepared to return. Hello Volunteer Rescue.
Whilst it was in the shop being diagnosed with a busted trim motor, I thought I may as well have the engine serviced, so gave locally respected guru his list of things to do and retired the scene. Later that same day, I got a call. Apparently the spark plugs were rusty, and it could be a bad problem. Next day I dropped by and we chatted about the problem, although the guru hadn't had time yet to really get to grips with a variety of tests and checks he said he would do.
The day after that, the guru is stumped. I say the boat ran and started well, which it did. There is no evidence of water in the cylinders, compressions are fairly uniform and about right, and although the gear box oil was mainly water with a lump of black stuff in it, no evidence either of corrosion internally, gear damage or most significantly, water getting up into the head or into cylinders from the exhaust. So though appearances of TLC can be deceptive, in the context of the gear oil, no apparent harm done.
So why the rusty spark plugs? Is it possible that plugs can rust inside the cylinders if the boat is not used for a long period? I knew when I bought the boat that it hadn't seen water for best part of a year. But if they had been rusty, wouldn't the two hour, high speed thrash have cleaned the rust up? Or over-coated it with oil/fuel burn?
Anyone have ideas how, if there is a problem, it could rust the plugs while allowing pretty good starting and performance? Any thoughts about what could be happening here? A problem lurking to bite me later, or a red herring? Any thoughts on what to look out for would be greatly appreciated.