The carbs on the Hyper .21 are notoriously sucky. If you can find an OS 20E carb on ebay(there's one now for $60), that would be the ticket. Also... how many gallons of fuel have been run through that motor? More then likely, get yourself a new budget motor... an OS .21 RG if you can happen to find one (discontinued), use the carb on the Hyper .21 until it dies, then throw it on the OS .21.