My 2GM15 is getting touchy lately when I am trying to back into my slip. After a run up to operating temp under load when I come back to the marina and switch into reverse, give some throttle to start moving backwards and then drop it to the idle position. Clunk Clunk and the engine begins to quit... sometimes it will come back to life but most times i hv to give it some throttle to keep it alive. Could this be bad fuel? I had the fuel over the winter and did not add any additives this year. All new filters, fresh oil, starts and runs fine all day. This only happens when the engine is good and hot. Any suggestions will be appreciated. Thanks Ed