One clean spark plug

[Tyler jones]

I have a 1994 mercury bayliner reflexx sportjet 90(hp)
I replaced the reeds with Boyeson 234 reeds, i installed a 3.5-7psi electronic fuel pump, 3 new coil packs (that matched oem part#), replaced spark plug wires with oem part number.
I took the boat out today and rode good for about an hour I felt like it wasn't getting full power, but it plained and scooted across the water, as I was cruising into the slip, I was about 2 miles out and it started to sputter and slow down at full throttle. I rode it for about a half mile to an island, as I was taking that slow cruise it would sputter like it was trying to bring the rpms up but never did, I pulled over, pulled the spark plugs, the top one looked new it was so clean, the bottom two was black brown sutty. I cleaned them,, reinstalled them and started back to the slip,, she hesitated and started to plain but did not produce full power. Now should I be concerned that the top one still looks new? I'm gonna check tomorrow if it has spark. If it is positive for spark would the possibility be a carb issue not sending fuel?

 

[Slabby]

A brand new looking plug on 4 strokes is often a sign that a head gasket is bust and letting water into the cylinder through a cooling port. Not sure how that theory goes for 2 strokes but can't see why it wouldn't be the same...

Run a compression test on each cylinder. That will give you some more info in any case. If I'm right then you'd expect to see a greater than 10% difference on that cylinder than the others. Often gaskets fail in between cylinders so you might see poor compression on the one with the shiny plug and the one next door... hope that helps