I was given a MTD Lawn tractor and I'm trying to get it running. I think it's been sitting up for a while. I've worked on small carburetors before so on this one I'm wondering where the fuel pump is. I poured fuel down the carburetor and presto. It runs great until the fuel runs out so I must have a fuel deprivation/carburetor problem, or so I'm thinking. I changed the fuel filter and used fresh fuel but it does the same. What should I check next? Thanks.