Where is it leading to? Have you removed the air filter assembly and had a look under it for any vacant vacuum barbs? Most countries have the Mikuni 32-35DIDTA type carbs. I think this is probably only the second truck engine I've sen fitted with the Aisin carb. I googled the Aisin 2 barrel carb vacuum hose layout and there are a number of different types - without a better look at your carb + manifold it's hard to tell.