If you are sure your tach is accurate, go back to the basics, check spark on all cylinders, check compression. Remove the front air box and make sure the bottom two throttle plates are opening, they are attached to the upper plates with a coupling that can slip. IF that checks out, take a spray bottle, put some gas in it. Remove the cowl and front air box of the engine. Have some one drive the boat at a moderate speed(3500) and spray a shot of gas into each carb. If a cylinder doesn't make any difference, you know that's the one not running, its either running rich or you have an ignition problem., if the engine drops rpm when you shot gas in the cylinder, thats a cylinder running good. IF it picks up rpm when you shoot gas in it,its running lean and isn't getting any gas. BTW, don't make a full power run with the air box removed, OMC products don't run lean at wot with the air box removed. I've got a 115 eagle series motor with the plastic carbs that's been kicking my but all summer, I finally scored a new set of carbs off of a V6 to try out on it, I've been thru these carbs four times and can't find anything wrong, but when I put the new carbs on it, it instantly ran batter. IF the loaner carbs fixes the engine, I'm going to order new bowls and main carbs bodies for the 115 and put them together with a new kit. They can be real frustrating.
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