The collet really isn't worth discussing. I've just had issues keeping a flywheel tight without putting shims behind it.
As for the pull start, it's depended on centrifigal force as opposed to a bearing binding on a shaft. With a lawnmower, weedeater, chainsaw, pretty much anything with a pullstart but rc nitro, there's a flywheel on one end of the engine and the output on the other end. The nut that holds the flywheel has bearings in it that settle into pockets when the engine isn't running. When you pull the pull start, these bearings sitting in pockets provide the catch. Once the engine is running, the bearings roll out of the pocket and the centrifigal force holds them out until the engine dies or is shut off.