I swapped out my stock fuel pump for a walbro. I started it and it ran fine, gave it a few revs too. But when i started to back up, it shut down on me and wouldnt start back up. There is no spark or fuel. I tried a used dizzy and main relay, still nothing. I dont here the fuel pump prime neither. What could be the problem??? I left it running for a good couple minutes and when i backed it out it took a shit on me. Please help. Its a dohc zc btw.