I have a yamaha MX 175 that i have been working on. I saved this bike from rotting in the garage about a week ago. I have pulled the fuel tank and cleaned the inside completely out. I have completly rebuilt the carburator. I check the plug and i am getting spark at the plug. i also checked the fuel line going to the carburator and i am getting fuel. I have tried to start the bike and i have gotten it to start twice in about a 5 hour period and each time i got it started the bike would run for roughly 15 to 30 seconds and die. Any ideas to help me out?

If you have a good spark it has to be the fuel? The carby can be a bit pesky to make sure all the jets and holes are clear sometimes. Are you sure that fuel is getting through to the cyclinder?