[MechWerks]

Also go over the float level setting carefully. Too many people ignore the float level like it is some simply on/off valve for gas from the tank. The gas level in the carb is set by the float height and how high the fuel sets in various circuits. As normal air flow through the carb pulls at various circuits and ports, it is apparent how a change in height determines how it can be either easier or more difficult to meter off fuel.

One of the more lost engine tuning arts is vacuum readings in the manifold. If you have ever played with adjustments while watching manifold vacuum, you get a feel for how one thing affects another. Mechanical timing, valve timing, spark curves and carb settings all change manifold vacuum. Since it is outside air pressure that pushes air through an engine the various effects on that pressure have significant impact on engine performance.

Similar engines are not the same and changes to outside parts further separate differences.

A hot engine can cause the intake air to expand, basically similar to going to altitude and reducing air mass, causing the A/F mix to go rich. Plugs foul at idle causing a stall. On the other end of th spectrum, opening the throttle from idle causes an air increase and a lean condition, the accelerator pump throw raw gas on the problem and usually prevents the lean condition. So a high rich or lean from incorrect accel pump setup can cause a bog or stall.

As Merlin Hawaii pointed out, this stuff isn't difficult, just attention to detail, and methodical changes and noted results. Random changes without assessment only leads to confusion and upsets the synergy needed in an engine assembly.

One passing thought....engine manufacturers will always recommend rich jet setups as a start...reduces the liabilty going rich instead of lean and burning an engine. And rich IS the correct starting point.