Yup, those plugs are rusty colored. I would assume it is because there is either some rusty sludge in your base starting to work its way through the system or it is from the crank and bearings having surface rust on them. Typically between the oil and the detergents in the oil, it will mix with the surface rust and help wash it off. It would appear that this is all you are seeing on the plugs, most likely it will clear out with a few tanks run through. The plug reading is a good practice and offers reasonably reliable evidence of what is going on inside. The color to look for is a nice chocolate brown tanning to show that the burn is clean and efficient. Tachs and exhaust temp sensors work too but only in certain circumstances, not too many of us have access to an isolating test tank to max out the engine and get true consistent tach or temp sensor readings. I know on Ultralight aircraft they need exhaust temp sensors and gauges but that is a totally different purpose and they have a dash to carry that kind of equipment.
Never try to tach a ski out on the trailer with only a garden hose attached, the results will never be accurate due to no pump load not to mention the damage that can occur. A garden hose can only put through about 3 gallons per minute with minimal pressure behind it. Not nearly enough to satisfy the demands of a prolonged wide open engine run. I think the pump could take damage too if I remember correctly...something about expansion of the impeller when run dry and contacting the wear ring, don't hold me to that but it seems to me that I have read that somewhere before.
The plug on the right does appear to be showing slight signs of proper burn color just above and to the right of the bridge, but just to be safe it would be a good idea to change them out a few times until they start looking normal again. Gap settings will have different results on color too. If it is too far spaced the plug will look white with a frost-like residue, that is indicative of either too lean of fuel and/or too much gap space. The more gap, the more voltage needed to jump the gap, more voltage...more heat. To small of a gap, lower voltage leaving a smooth dark almost black porcelain insulator with a wet look from lack of proper ignition and/or too rich of a fuel charge.
ops this afternoon with fresh plugs I'll post those pictures up also.
