To get real help, a carb number would be needed. Also, when you say "rebuilt", you mean rebuilt by who and what was done to it exactly ? and what type of parts were put in ? Do you know that auto parts stores "kits" are junk, as they are not suited to today's new fuel ? If one of those kits was installed, carb will be very difficult to stay in shape very long. Sometimes a few hours is all it takes for the rubber parts to swell and become useless.
The 50M metering rod suggest it's a truck carb, unless parts have been swapped.