Try checking to see if you are running on one cylinder. Those motors are tough and will run decent on one cylinder but half the power.
Change your plugs, there cheap enough. (might just be a bad plug hopefully)
Spark plugs- (torque to 17 to 20 foot pounds with a torque wrench)
Spark plugs gapped at 0.030 (use a feeler gauge)
Check to see if you have good spark on both cylinders using a spark plug tester, not just a spark on the end of the plug. Yes grounding the plug against the motor can let you know if there is spark, but it does not let you know the quality of the spark. Low quality spark (on a spark plug tester) could be oxidized or improperly gapped points.
( Please undo both plugs, so you don't accident start the motor) Should have a good strong spark at 1/4 to 5/16 inch on the spark plugs tester. (ground the tester to the motor). If you have a cylinder that has no spark or very weak then your basically running on one cylinder. Father in-laws Evinrude 6hp motor was running ok and idle a little rough but it was running on one cylinder, no spark on top cylinder and was running about half power. Had to change the coil on the motor and now it runs smooth and he is happy again. These motors are tough and will run on one cylinder but poorer than usual.
Another way to tell if you are running on one cylinder is to start up the motor(in the water) and let her warm up for a minute or two. Carefully (don't want to get a little jolt
) unplug the boot to the top plug, if runs rough but maintains some then the bottom plug/connnected cylinder is firing. If it dies then you know that the bottom cylinder is not firing/spark. Replace the top spark plug boot carefully and let a run for a minute or two, then unplug the bottom plug boot, if it dies then you know that you have the top cylinder plug/wire that is not firing/spark. If runs rough but maintains some then the top cylinder is firing.
spark plug tester $7.00
feeler guage $7.00
torque wrench $21.00
**Make sure your vent plug is open plug on your tank open when your running/starting your motor if you have a plastic tank. (You may laugh, but all of us have forgotten to open that vent plug while starting up the motor in the morning for a day of fishing and find a little while later the motor is running like do do, because the air can't entering the tank. The motor's and fuel pump is now trying to suck gas from a tank that has a negative pressure in it. **
cajuncook1