View Full Version : 50hp 2 stroke, overfueling / high idle?!

08-21-2019, 05:45 AM
Hi, I have a mercury 50hp 2stroke (3 cylinder, 2 carbs). Iíve rebuilt the carbs and changed all the fuel lines, and cleaned the fuel pump. Started up after a couple of tries but the idle is too high, and excess fuel running back and dripping out the bottom carb, assumably mixture control screws.. what do I set them at and is there anything else to check?

also donít know too much about the engine as itís a Belgian one and only serial number on it I canít find to match to anything.. (09629963) think itís early 90s? Has the two tone grey, red, and black banding around it. Thanks very much! Desperately trying to go out this weekend 😩

08-21-2019, 07:36 AM
Remove the lower carb and do the rattle test: Shake the empty carb and listen carefully for the float to rattle about inside. If you don't hear anything, remove the bowl and carefully sandpaper away any flash on the front of the float. Seen several of these carbs where the float 'grows' over time and sticks.

The idle adjustment on these motors is extremely difficult to get right. With the motor in barrel, I use an infrared temp gage on the plug metal body and keep diddling way on the idle mixture screens until all there plugs read similar.

The motor is best adjusted in gear with the boat on the trailer or tied to a pier. Add a 1/4 to a 1/2 turn OUT on the mixture screws if it bogs on throttle up.