I recently acquired a 1993 Snapper P21500 self-propelled mower with a Briggs "Signature Series" 5.5 engine for free - - mower starts easily but I'm having issues with a dodgy and sensitive throttle control. It will seriously over-rev on high speed throttle, and seems to hunt for the correct RPM when it's under load while mowing. I'm guessing it's something to do with the governor, I've attached pics of what this carb looks like. No primer on this model. I'm not sure the governor spring is in the proper location, but haven't been able to find a diagram anywhere. Engine is a 128802-0211-01, 93090359. Maybe it's missing something, thank you in advance for the help!