Ran fine now wont start

I purchased a used Hustler mini model 927236. I used it last weekend to mow for several hours with no problems. I ran on tank to almost empty then switched to the other tank, it did not run out of gas. This weekend it wont start, it cranks but wont start. I changed the battery as it was the original, same thing, cranks but wont start. Any ideas what I should try? Thanks.
Rick