The lack of change I was referring to is that it won't run above an idle. No matter what I have done, opening the throttle results in sputtering, coughing and stalling. My first instinct, and the only thing I have not tried, is the manifold, as that is the only part I have used on both engines with similar issues but haven't swapped out for something else. Could there be a pin-hole in the casting causing my issues?
