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I have an interesting problem. I got a used EM650 that reportedly had a surging problem. So since it was already drained of gas for movement, I went ahead and pulled and cleaned the carburetor.  I reassembled  and  it still  has the surging problem.  Here  is an interesting fact that may be a clue... It was very difficult to start and I found that it started only when I pulled and lifted then generator while pulling. So in essence it has to be thumped against the ground in order for it to start and then it surges. Any ideas? Thanks