Hi Norm,
A few things you could check below but may not be the problem as I've taken the primer bubble off before and found a one way valve
has popped out and sometimes seen a jet popped out .
These sprint carbs will over fuel if the two tangs on the diaphragm are not sealing properly (2 Fuel Pump Valves ) usually you can tell straight away by how the fuel primer works ,once fuel is in the carby each press on the primer should shoot the fuel out in a strong steady
stream if not the diaphragm valves aren't sealing properly. The valves should seal as you've fitted new diaphragms but they don't
always seal.
I don't know if that's your problem without looking at the carby but if you can feel air in the primer when pushed or the primer
isn't pushing or a lot of fuel the poor sealing valves could be the problem.
Another thing I always do is remove the 2 metal fuel screens and blow everything out with compressed air.
If the spring in the diaphragm is longer than normal it can make them over fuel.
Cheers
Max.
