Outboard engines, whether two- or four-stroke in design -- are just as sensitive to air/fuel ratio problems as their land-bound counterparts. Two-strokes encounter another complicating factor in the form of oil mixture, which can often duplicate the symptoms of a lean-running engine. If you suspect that your engine is running short of fuel, you need to address it immediately; the next sign of trouble you get may well be a melted puddle of aluminum where your engine used to be.
Check your temperature gauge. Lean air/fuel ratios will always make an engine run hotter, and this is especially true for two-strokes. A two-stroke engine depends on a constant flow of fuel/oil to keeps things running cool and calm; a fuel deficit will also starve your engine of oil, which will generally cause overheating at anything above idle.
Listen for a backfire. Engines with lean air/fuel ratios often encounter a condition called "lean backfire" under sudden deceleration. The lean condition may introduce too much air for the engine to burn all of its fuel on the power stroke; suddenly closing the throttle will temporarily choke the engine, allowing the mixture in the cylinders to fully ignite. Unburned fuel in your exhaust will ignite once the burning fuel hits it, causing a backfire.
Feel for a loss in power when you open the throttle. Lean engines will typically run best when the throttle is shut and choking the engine. Once you open the throttle, the engine runs short of fuel and fails to detonate the mixture. The result is that the motor will actually lose rpm when you open the throttle and regain it when you let off.
Pull the spark plugs and take a look to "read" them. A lean-running engine will typically turn the spark plugs a white or very ashy color. Under really extreme conditions, excess heat in the combustion chamber may have caused detonation or pre-ignition, melting the plug or cracking the ceramic insulator. If you see little spots on your plugs but the engine is still running, then consider yourself lucky; those little spots are molten metal, signifying that your engine was on the verge of self-destruction when you pulled the plugs.
