The impeller on my outboard motor (2002 2 stroke 75 HP Yamaha) was replace last year before I used it. It was fully serviced at that the time, but the motor hasn't been run in about 12 months. Does the impeller (for the water pump) go bad if it isn't exercised regularly?
Doing a quick google search for "Impeller 2002 2 stroke 75 HP Yamaha" shows that it is a rubber impeller, these WILL age and dry out.
Check your manual for when and how to replace it.
As a rule of thumb:
On inboard engines we replace these yearly, it's a cheap 15 minute job that can save thousands in damage.
On our outboards I think we should be doing the same but we actually only do it every 5 years.
We've been lucky and my favourite outboard (2stroke 6hp Mercury) sometimes sits for years between usage and always works without a single issue.
For both inboard and outboard engines: while running the engine regularly check if water is still being pumped out (on engines that support it make sure your engine (and wet exhaust) temperature alarms work and hook up a good buzzer). If no water is being pumped out and the engine is hot (sometimes engines have thermostats) get out of the way of any traffic and stop your engine.
Call for help and get a tow back.
Edit your question, then I will edit this answer:
What is the symptom of not working?
A: The motor won't start.
- Check fuel
- Check that the spark plug works.
- After this it's pretty much 'my two stroke engine won't run'
B: The motor starts but runs really rough and develops no power.
- Dirty gas.
- Clogged carburator.
- Somebody ran it on unmixed gas and scored the cylinder/piston badly enough you don't get much compression. This is easily tested.
C: Motor runs fine, but the prop doesn't spin.
- broken drive shaft.
- broken shear pin.
Note: Read your manual. Many engines are water cooled, so running without the bottom half in a water tank can result in a very large paperweight.