Thorp Air Command - T18.net

Years ago I had a Lycoming that would pop and fart when running on the ground (sea level). I asked a Lycoming about this and his commment was, " If not under full power, lean it". He indicated you can't hurt the engine. Some guys run lean of peak all the time. This meant at any altitude. I lean mine on the ground and as soon as safe altitude reached I lean.

Let me know what you find out when you check it out Rich....Dan

JP: I've been searching for that Lycoming New Letter regarding jet sizes and have not found it ? Do you know the NL# or Flyer reference.

RB

The same carb will perform differently depending on gravity feed or fuel pump. Fuel pumps usually cause the engine to run richer. You may want to make sure you are comparing apples to apples.
Don Pridham's GPU book listed some things they tried to set the MA4 carb for an over rich condition on the O290. One was to install a sleeve in the throat of the sump reducing the size. The O320 sumps apparently have different size throats. I will upload the pages to my photos.

Bob