I haven't started my 351 engine in 2 yrs until a few days ago. When I put it in gear, it act and sounds like its running on 7 cylinders. Lacks some power, but it idles fine. I haven't run it very long so I don't know what to expect. Could it be a valve problem? It did smoke alittle from the valve cover area before I put it away in the garage afew years back. Thanks