Ok so with a little bit of Liquid Wrench and a lot of patience, I finally got the thermostat housing bolts loose without breaking anything. This motor is only 2-years-new to me, so I’m not sure when the last time these came off or how old the T-stats are, but they are definitely not working properly. I tested them on the stove and could only get one of them to budge at around 165F.
Decided to go back and flush the motor with the T-stats removed, and the piss-power increased by 2-3x, which is the most I’ve ever seen on this motor.
Also, these spark plugs are exactly 1 year old, but notice how all of the head cover bolts and spark plugs are corroded on the port side of the motor, while all of the bolts and plugs on the starboard side look brand new. Did something happen within the last year to do this? I check for leaks while running often, and I’ve never noticed anything. So not sure if it’s simpler or more complex than I’m thinking…
Ok I had time to do a compression test tonight, and every cylinder had basically the exact same reading: ~130psi with throttle valves closed, and ~135psi with throttle valves wide open. I bought a cheapo gauge, so the values might be slightly off, but at least they’re all consistent.
However, I noticed oil around the spark plug holes, and the spark plugs look a little fouled to me, but I could use some help interpreting them. They’re all 1 year old.
Still trying to track down the source of corrosion on these bolts, seems less like a blown head gasket now…
I’d change the plugs. You are running rich, but that could just be from extended idle? I’ve always read plugs after a hard run. Many charts online to compare yours to. As to the corrosion on one side, I’d guess a little leakage around the hose. Only takes a little salt water sitting to cause that kind of rust/ corrosion. Not always, but I mostly remove my cowl and spray it down during an after use flush. I spray everything with oil. I’ve had some on here say that is not good for it, but I’ve been doing it for 30 years with no ill effects. I’ll at times even spray STP son of a gun over everything under the cowling.
Remember on the charts that you are running an oil burning 2 stroke. You don’t want em looking a little tan. I’d rather see them darker than it running too lean.
You got good compression. Odd that one bank is rusted on the outside and the other isn’t.
Grounding on port bank? Leaking hose at thermostat port?
Port side got hot at one time??? Engine sat in salt water for extended time???
Too many things to chase on a twenty year old motor. Change the thermostats and run it.
Clean off corrosion on the electrical connections and spray electrical grade silicone on it and invest in towing plan.
