Glossary “lean roll” Definition:
To turn carburetor idle mixture screws in enough to effect a slight rpm drop, causing a leaner mixture. This can cause the idle speedrise and fall, causing the idle to roll.

Glossary “lean A/F mixture” Definition:
Condition in which the ratio of air to fuel contains more oxygen than is nneded to completely burn the quanity of fuel.

Glossary “Lean Burn” Definition:
A Chrysler electronic engine control that appeared in the mid 1970’s. It maintains precise control of the spark timing to allow a very lean mixture to burn properly, reducing emissions using an analog computer.

Glossary “lean misfire” Definition:
Condition caused by a vacuum leak or open EGR valve, that results in incomplete combustion, causing one or more cylinders to pass unburned fuel into the exhaust system, resulting in an increase in hydrocarbon (HC) emissions.

Glossary “lean mixture” Definition:
A/F mixture with too much air, having more than 14.7 parts of air for each part of fuel (by weight).

Glossary “lean out” Definition:
1). To increase the portion of air or decrease the portion of fuel in an A/F mixture. 2). To decrease the portion of nitro in a fuel mixture.