Make sure you are shifting it at very low idle speed. Outboards have a built in mechanism to keep owners from shifting at too high rpm and damaging the drive train.
It is quite possible that your clutch is not disengaging the transmission from the motor. Also, your synchros could be bad, which would not allow it to go into gear.
synchro plates went out
Change the abs motor.
Switch to 4th gear!
If it will shift when the engine is off, but not while it is running your clutch is not working
If it has a hydraulic clutch, it is probably the slave cylinder. You could still have pedal but the slave is letting the fluid past the seals. Have someone watch the slave while the clutch pedal is pushed.
Align the neutral lockout switch.
have a pontiac 6000 2.5 motor and it wont stay running
you just suck at a stick shift
6 horsepower? That wont make it past 5 mph if that is what you are hoping for, Is it a troller? If it is than that is meant for shallow water with a fishing boat...
Perhaps the spark plug system is not sending electricity to the spark plugs.
If you have bleed the system and If it will not go into gear with the engine running, the clutch pressure plate may have failed.