A two cycle engine without a super charger is essentially a two sided piston pump. As the piston goes up on the compression stroke, the back of the piston is drawing a fuel-air mix in through the carburetor. As the piston goes down on the power stroke, the back of the piston is increasing pressure in the crankcase. The exhaust ports open first to relieve pressure and get the products of combustion moving in the right direction. When the transfer ports (AKA – bypass ports) open the pressure in the crankcase should be equal to or greater than the pressure in the combustion chamber. What could possibly go wrong? Unfortunately, many things. If the piston skirt is worn, crankcase pressure can leak out the exhaust. If the piston rings are stuck, compression (and efficiency ) will be lower and the crankcase charge will be contaminated. The underwater exhaust compounds this by increasing exhaust pressure to displace water. The loose bearings of a worn out motor also leaks away crankcase pressure. Many drill holes in the exhaust pipe to lessen pressure, but may not help enough on a worn motor and significantly increases noise. Small pistons are very sensitive to piston ware. Sometimes switching to a SAE 40 weight oil will help. TCW-3 oil is a disaster in these old motors. It lubricates well, but does not seal a loose bronze bushing. A border line outboard may produce enough power to keep running with no load, but anything that uses power (displacing water or turning a propeller) takes away the power to keep the engine running. . . 🙄
