I have a '46 Oliver 70 RC with a carb problem.  When got it was missing the carburator.  Managed to get one but the venturi was broken, got it running by using JB weld to put the venturi back together.  Later got a venturi that was suppose to be the correct one (unfortunately did not look closely at the size).  Found out it would run with new venturi but would not speed up beyond about half throttle, then dies.  This venturi had a ID of 1/2 inch, found one with a ID of 3/4 inch.  With the larger venturi will only run for a couple of seconds before quits.  

Does anyone know what size venturi should be in this carburator and where I could get one.