I have a 50 8N front distributor. I disassembled the carburetor to clean and rebuild. When I removed the choke plate, I noticed the hinged relief valve on the plate. According to the service instructions for the M-S carbs, it is normally mounted with the valve up and there should be a spring to hold the valve against the airflow. Mine was mounted with the valve down and against the airflow and is missing the spring. It looks like the only time it makes a difference, is when the choke plate is closed. Is there a replacement spring available, or should I just replace the assembly? The tractor has been running OK without it since I bought it a few years ago. I am cleaning the carb because suddenly a few weeks ago, it wouldn't run without holding the choke out. It happened while I was cutting brush. I have checked for fuel flow and that pours out of the drain plug on the bottom of the carb at a good rate.