In the dim recesses of the mind...
I don't have a whole lot of Bell 47 time, but I do have some - mostly in the G-2 with the Lycoming 435. Having said that, I never remember using, and never remember any other pilot using the "starter vibrator" switch (or whatever it was labled) on the panel. Mostly, we used to prime the hell out of them (four or five good runs up and down with the throttle), leave the mags off, engage the starter, then switch to "both" after a couple of revolutions. Started right up!
Alternatively, I knew guys who would start their ships on the right or left mag (I forget) and then go to "both" after it lit.
In the winter, during very cold weather (like below 30F), the engines would sometimes briefly fire up for a moment, but the condensation on the plugs would then freeze and the engine would die until preheated. (At least, that's what the mechanics told us was happening. Even it it wasn't technically true, preheat was a must at that point. If it fired but quickly died, it would *never* go again. You'd run the battery down or crank forever with a battery cart. We learned the hard way to just roll 'em back inside and heat 'em.)
Like I say, I often asked pilots with a lot more 47 time than me what that "start vib" switch was on the dash. Nobody knew, because nobody used it.
And our 47's always seemed to start.