RE: bench starting a engine. NO NEVER
Good way to break-in an engine IMO. Since I mod engines all the time (21's thru .30's mostly) I break them in on the bench most of the way. If a customer wants it test run on a boat then thats what they get. I can usually get the needle very close so he doesn't have to spend a lot of time finding the needle for his hood.
The method I use the radio system is on the bench turned off, it won't be needed until the sixth or seventh tank. I go for 1/3rd carb opening, needles set rich, very rich. I choke and by pinching the fuel line I'll get the starter going with that fixed 1/3rd carb opening.
Some times too much fuel will accumulate in the muffler or pipe,, put hemostats on the fuel line and dump it out.
Go back to pinch and starter,, once its going the richness will want to kill it,, pinch or pinch in succession to keep it alive. You now are the fuel metering for the engine. I use a heat gun in one hand and the other is the pincher. I keep the them down to 125* on the first couple thanks and move higher with each tank. You can run the needle "in" a couple clicks if you have to pinch steadily. later in the tanks its up to 175*- 185* and up and I'll pinch it to run up in rpms and let the richness bring it back down.
In muffler engines like the O.S.XM o/b and Thunder Tiger its possible to get a runaway in rpms cause of the no limiting factor the muffled engines have. They'll just feed off their own creation of fuel pressure and heat and become a runaway jet turbine. Not to be worry tho, your the one metering the fuel,, just brush the carb opening with your finger and choke it back down. around the 7th tank you can pick-up and turn on the transmitter with most engines and get your needle limits roughly set.
All this is done with more fuel and lube than that engine will ever see in normal operation. Your also building important heat and monitoring it. You want the engine to swell and run-in its surfaces where necessary in a safe lubricated manner. Every auto engine comes with a thermostat and most are set to open the cooling at around 190*. If its important to a car, trust me, its important to your little model engine.
uhhh,,"bench starting"?,, you must be talking about something else. anyway you have a great method of breaking-in the engine here.