I work on many planes that have had the "one piece" put in. Not one had the problems you describe. They all had a roughness at full throttle that smoothed out at about 1/4 to 1/2 inch back from full throttle. Actually the "old venturi" is one piece that is held in by three spider piece wedges that could have fallen loose thus the service letter and AD. Most were tight and took a lot of force to dislodge. There is a fix from the builder. Do contact precision or whowever owns MS this week for details something about a new spray bar I think to compensate for a length difference in the old and
new venturis as I recall. Your mechanic should know about it as it involved a lot of C-172's especially. I'm not convinced that it's your actual problem./tom
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