Meaning, don't let it run, for any amount of time, on ether.
Say you go to kick your bike and nothing happens. Well. If you're not interested in removing your seat, gas tank, etc to allow you to pull the plug and check of spark, and to hook up a compression or leak down tester, BUT still wanna see what your problem is, ether is a tool.
We need fuel, compression, and spark for our scooters to work.
If you have a no-start condition, there's a good chance its a fueling issue. Quick way to check--- spray some ether. If it starts right up, you have a fueling issue, most likely. Even if it tries to start, there's a very good chance your problem is with fueling.....
But here's why we don't let it run for long-- ether, aka starting fluid is very volitale. It can light of, and facilitate a combustion event, in circstances where the engine may not normally be able to on its own.
It's important to understand that you'll never FIX anything with ether, unless your problem is one like say.... Priming the fuel line/filter after winter on a riding lawn mower where the fuel has a long way to travel before it gets to the carb. Mine was having a heck of a time getting the fuel filter filled up with fuel, as it sits before the fuel pump. I used an external fuel can plumbed directly to the carb to finally get the engine running, so there would be enough RPM to turn the fuel pump fast enough to prime the system. Ether would've worked too.
Here's another issue. The Base mean effective pressure of a charge of ether lighting off is SUPER HIGH. It's not uncommon for it to collapse the ring lands on a cast piston. I've got a picture of it, if anyone wants to see.