Re: Mercury 9.9 4stroke Hard starting,poor running
Its been awhile since I've worked on a Merc 4-stroke, but here's what my past experiences have shown me - The fuel passages in these carbs are very small & it doesn't take much to block or partially plug them. Use of a fuel stabilizer (year round) is an excellent idea.<br /><br />I had a few (3 or 4) act this way right out of the box. I pulled the carb off and carefully took it apart (inside the shop on a bench, on a clean towel where I wouldn't loose any small parts). Althought they appeared spotless, I washed all the aluminum alloy parts with spray carb cleaner and dried with compressed air, paying close attention to all small drilled and machined passages. I re-assembled the carb, making sure float settings were correct. I removed the plug which hides the adjustable idle needle screw and set it to the initial dimension. Re-installed carb on engine and started and ran engine in a test tank (tank MUST be deep enough to simulate depth of water in/on mid-section when boat is in water). I adjusted the idle needle richer until I attained a nice smooth idle and acceleration. Coincidentally, starting was much easier.<br /><br />-John
