Dave,
1. Did you put the governor tube back on the casing?
2. When you replaced the 'O'ring on the starter did you check that it was sealing before you tightened up the 3 bolts?
3. Did you remove the cable from the carby?
4. Can you give us step by step what you did when you did the repair so that it easy for us to give you the correct answers to your problem.