carb adjustments

[38plymouth]

I have a 1996 evinrude 3 cylinder 50 horse. I recently rebuilt the carbs because they haven't been touched in a long time and it was running a little rough under 3,000 rpms. I have owned the motor about 8 years and don't know if it was ever messed with. The carbs were very clean inside and I made sure that there was nothing plugged before putting them back together. I set the low speed needles at 1 1/2 turns out (where they were originally)and the engine pretty much runs the same as it did before. From 3,000 rpms and up it runs very smooth and strong. Under 3,000 and it stumbles a little and it surges and tries to increase rpm if I run it at 2,000. It idles at 900 and is a little rough but never stalls. I put new plugs in just in case but it didn't help. What rpm range do the low speed screws cover and when does the main jet take over? I always thought it was around 3,000 rpms so I figured the low speed needles need to be adjusted better. I was hoping to get this adjusted myself, the marina here is booked for weeks if not more right now.