when cleaning them is not enough - the inner passage should be 1 1/2" give or take. The engine should run with the amount of work you have done but will not be quite what it should be. Due to the inner reverse thread it is pretty difficult to manufacture one without some pretty serious machine shop facilities coming into play. Your old coupler may still be useable but the cast gooseneck might well have to be replaced. Before I did that, I would drop it by a good automotive machine shop. They have caustic hot chemical treatment vats which can sometimes do wonders - it's how they clean carbon and mineral deposits from engine heads, manifolds, etc. It's always worth a try. When they are through with the process you may find the unit rusted out to the point of perforation and wanting replacement anyway. These sometimes come up on ebay at a considerable savings.