merc help

[salvagefirst]

i have lost 2 cylinders on my 89 seacraft 200 merc carb motor,both on the left bank,replaced batteries,filters,changed plugs,compression reads 115 to 120 on all cylinders even switched the powerpacks around without a differance.pulled the plug wires one at the time all had good blue arc. Winter fishing it would not get up on plane till after about 5 minutes then it would start hitting and run fine the rest of the day.could bad reed valves cause the problem? Thanks Les