Re: 72 Merc 115 Six Banger
Should be around 120# optimum but a consistant reading across all six cylinders is more important. If you have say 110# plus or minus 5# across all six that's better than 4 with 120# and two with 70#. If your compression is a little low - say in the 90# range try giving it a good decarb - works wonders and may very well bring your numbers back up close to where they need to be. Make sure you run the motor for a bit then pull all the plugs and check the compression. This wets the cylinder walls and the rings and gives you a more accurate reading. If you drained the carb bowls for the winter and this was the first time you tried to start it the float in the top carb may just have stuck for a bit-- my 1150 (115) does this occasionally on 1st start up in the spring but the problem goes away immediately - if not in your case time for carb kits---remember you need parts for 3 carbs-- most kits contain parts for one carb each.
