Could we be talking piston rings??
One might attempt decarbonisation....it might make a difference....
Years ago, GM had a Top End Cleaner, but iirc, they dropped it...it would eat paint, and I suspect too many claims.
One could research this topic, but my scans suggest Johnson Evinrude OMC Engine Tuner 777185 is excellent...but again, I'm sure it will eat paint also. Hence, where its sprayed on a painted surface, kiss that paint goodbye.
I may try this on my 1993-245...I would use an intake vacuum port, and spray can into the biggest vacuum line, with engine running on a fast idle, say 1500 RPM. I'd leave engine off for a full day...after re-starting, and running, I'd then do an oil/filter change. Also, one could remove sparks, and spray directly, and reinsert (not tightened), after engine is off
Note - I have no idea what happens to O2 sensor, or Cat
Via Amazon reviewer
I'll try to keep this brief. I've used this for 30 years, it works. I've brought things back to life, allowing the product to sit on piston crowns and soak into the ring lands. It will turn carbon into butter. 2 or 4 stroke, works great on all. I always use on my engines as the hours go up. On an assembled unit I spray liberally into the intake until the engine stalls or if a large engine until it sputters hard, then shut down before you pull away from the intake. No walking to the key switch to turn off, you want this stuff to lay in the engine. You want to dispense plenty to assure it gets messy in the exhaust as it will break down the goo. Let this sit for at least 24 hours, several days, even a week. I assure you, when you start the engine it will shake and stutter, smoke and black yuk will come out the exhaust. Run the engine up and blow all the gunk out! Don't allow anything to remain and burn back in. WOT is best. You will notice a better running engine, smoother is what I always see. Most stuff you dump in an engine may or may not do anything, hard to tell. Usually a change is in your head. This stuff was invented in the days of the old dirty 2-stroke outboards which needed to be decarbonized on occasion. It's as close to magic in a can you'll likely ever get. Expensive but works. If it doesn't either you had a clean good running engine already or you have a mechanical issue which needs to be addressed.
