'99 Mercury 50HP ELHPTO: carburetor idle screw adjustment procedure

[ironring1]

Hello, all. I have a 1999 50 HP ELHPTO 2-stroke, 3-cylinder outboard (s/n 0G905364). I recently pulled the carburetors, disassembled, cleaned (I love my ultrasonic cleaner!), and reinstalled. I recorded where each of the carbs' idle adjust screws were before disassembly (all around the recommended 1 1/4 turns out from bottom). The engine fires right up, but I want to properly set the carburetor idle screws

I understand the link & sync process, engine idle adjustment, etc. What I don't understand is the process to adjust the individual carburetor's idle screws. How do tune this? I know how to adjust the carb on an engine with just one, but I've never done this for a multi-carb engine.

 

[Chris1956]

In the past Merc idle adjustments have been a compromise between idle quality and acceleration. That is when the carbs were set for best idle, the motors would not accelerate smoothly. This is because of design and the lack of accelerator pumps on the carbs. If your motor does not have the accelerator pumps, you will need to set the carbs a bit richer to achieve acceleration.

So, if you do not have acceleration pumps, set the carbs to initial adjustment. Warm up the motor in the water. Now, idle along in the water, and set the carbs to make the smoothest idle. Now try to accelerate. She may stumble and not accelerate. If she accelerates smoothly, you are done.

If not, open the top carb 1/8 turn and try to accelerate. If no go, open the next carb below 1/8 turn and try to accelerate. Repeat with all carbs, top to bottom, testing acceleration after each adjustment. If that don't get it, repeat the process, top carb to bottom.

it might take some time to dial it in. The inline engines tend to run a bit richer on the bottom cylinders due to gravity on the oil and fuel recirculating systems. They are likely to use less mixture for idle.

Once you have good acceleration, and the idle smoothness is acceptable, you have adjusted it properly.