I have an Americana snowblower and found a manual for it on internet and it tells me to use a 30" belt for the auger. So I got one put it on and the belt is so tight that the auger runs all the time. What is the next size of belt should I use? I tried adjusting but it did not work.

Try a 31 , some companys used 1/2 size belts as in 30 1/2 ,when you go to buy a replacement one sometimes they drop to the size smaller .
Luck

Thank you for your answer I will try this and see what happens.