Walbro carbs come from the factory with a small spring and ball detent..The ball fits into a depression in the shaft..If both are present the choke can NOT vibrate closed..If the choke shaft was removed and replaced the ball and/or spring might have been lost....
There a a few Walbro carbs, HDA 6A being one, that have a spring loaded link on the end, but I don't think the Ryobi carb is one of these...