1995 basstracker mercury 40hp motor issues

by Chris
(Reno, NV)

i have a 1994/1995 bass tracker with a 40hp Mercury 2 stroke motor. we recently had the carbs cleaned out as the boat sat for about 4 years with no use. I have replaced the throttle cables as one was broken. The issue we are having now is:

The motor starts fine and it usually needs a little choke when i go to full throttle. Once the boat is at full speed, the boat runs fine. But, when we get into trolling speed, the motor will run fine for about 15 to 20 min. At that time, the motor dies. I can usually keep it going by pushing the choke in. Any suggestions on what is causing this? i thought it may need a carb adjustment but i cannot find anything online that shows how to do this.

Thank you and i appreciate any feedback. Happy New Year