Pelican Parts Forums - Why do we increase control pressure on acceleration?

dduclaux,

It is necessary to adjust the air-fuel mixture for different operating conditions such as idle, part load, or full load. Typically, you need a richer mixture at idle and full load, and a leaner mixture in the part-load range for good fuel economy.
The correct air-fuel mixture at idle, part load, and full load is arrived at by the shape of the air funnel at the air-flow sensor plate, and fuel enrichment from the WUR. If the air-flow funnel had a purely conical shape, the result would be a mixture with a constant air-fuel ratio throughout the sensor plate range of travel. The air funnel is designed so that it becomes wider in stages. The funnel is shaped so that a richer mixture is produced at idle and full load, and a leaner mixture at part load. This combined with the WUR response from engine vacuum, results in a variable air fuel ratio for different driving conditions.