Motor not getting to high enough rpm's to engage cylinders 3&4

by Kale
(North Platte, Nebraska)

I have a 2004 Mercury 115 elpto, ser#OT856541, mod#1115412cd. I believe this motor should push my boat at aprox 40+ mph however, it seems to only push at aprox 20 mph. It has 4 carbs on it with the top 2 having adjustment screws and the bottom 2 do not. I believe this means it's a 2+2 and the other 2 carbs kick in at higher rpm's. I don't think it is kicking the other 2 carbs in and it seems at full throttle the motor is hitting aprox 2000 rpm's but I don't have a gauge to kno for sure. What can I do to get the other 2 cylinders to engage? How do I get higher rpm's to engage the other 2 carbs/cylinders? Can I put adjustment screws in the bottom 2 carbs? Any help would be appreciated.


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