This is a motor question but also a jet boat question...for all intents and purposes, the motor is running great (BB 454), accelerates hard, idles nice, sounds good and starts...exactly what you want a boat to do lol. But changing the plugs yesterday they were very dark and smelled of gas or gas/oil mix. No buildup, clean but just dark and wet looking. Looking through the plug hole in the heads into the cylinder I can see the tops of the pistons and they have what I think is a lot of black, sooty looking carbon buildup on them. More so than the usual dark/blackish oil burn glaze that engines always have. Pistons are forged small dome, block is .030 over and has about 2 seasons on the rebuild(new pistons,rings,machining) Motor is TBI fuel injected, and TBI and injectors are new as well. Spray pattern in good. Fuel pressure reads around 28psi at the line in to the TBI. Base timing is around 2 degrees BTDC with the auto advance locked out, and then the computer auto advances it to whatever...don't remember off hand but I think it's like 12-15 at idle and 32-ish at WOT. Motor does not have a thermostat. Original motor that came with the boat didn't have one either. Temp runs around 125-145 idling and 110-125 at WOT. This is in SoCal/Arizona lakes and rivers. Plugs are standard ACdelco R34T with .035 gap. Engine compression is approx. 10:1. The main question here is, is this buildup common for a cool running BB 454? Should I be running a thermostat to bring up the temps for more heat inside the combustion chamber or should I switch to a hotter spark plug? Or advance the timing more to lean it out? Thanks!