Small Engines (Lawn Mowers, etc.): 25hp Johnson outboard low speed problem, lean mixture, speed problem

Question
I have a 1971 Johnson 25hp outboard motor.  I am unable to troll with this motor without the motor loading up and quiting.  I have a rich / lean knob on the motor but adjusting this has not helped.  The motor is stored indoors all summer and winter and the carb was redone 2 years ago.  Is there anything I am overlooking to fix this?  Are their any websites that have a carb schematic to work from if that is the problem?  

Thanks in advance for any help. Please feel free to post this on the site.

Answer
If the low speed (rich / lean) mixture on the engine doesn't affect the engine, and it should, the carb has a blockage.  If it does affect the engine but there is still a problem, it could indicate an issue with the ignition system.  Let me know if the rich/lean adjustment has any effect on the engine running at low speed.