I have a 1989 (I was told when I bought used) Mercury XR2 that is an excellent running engine. I do a lot of slow trolling with it and have no problems whatsoever. Compression on motor is 140 to 145 all 6 cylinders. I am leary of the decarb spray because on my previous motor, 1982 Johnson 150,I decarbed as a preventive maintanence ,and high speed jet in carb on top cylinder plugged and I ended up throwing a rod through the engne case. I guess you can see why I have second thoughts about decarb spray. Are there any warning signs of an engine that is too carboned up? As I said beforer the engine starts easily and runs excellent.