Chapter 9 Ignition Systems page 147

Basic Ignition System Operation charge builds up in coil (12 volts in) creates a magnetic field (windings of wire) voltage is stepped up (secondary windings) switch open (magnetic field collapses) high voltage discharged (to plug)

Fundamental Electrical Principles Electricity is lazy Electricity wants to go to ground electron theory (-) to (+) conventional theory (+) to (-) Conductors Insulators

The Electron Theory Electricity moves from – to +

Electrical Units of Measurement Volts---- Push V Current ---Quantity A Resistance ----Resistance to flow 

Ohm’s Law E = I x R E / I = R E / R = I E I R

Magnetism Alike charges repel (-) (-) Dissimilar charges attract (-) (+)

Magnets & Electricity Magnets can be used to for electricity Electricity can be used to form magnets Electricity when applied to magnets make stronger magnets

Ignition Coils Coils of wire wrapped around an iron core Step up transformer

Spark Plugs Spark plugs contain an air gap for electricity to create a spark and make a seal

Heat Ranges The difference between a "hot" and a "cold" spark plug is in the shape of the ceramic tip. The manufacturers will select the right-temperature plug for each engine. Some engines with high-performance naturally generate more heat, so they need colder plugs. If the spark plug gets too hot, it could ignite the fuel before the spark fires It is important to stick with the right type of plug Engine that burn oil may need hot plugs

Measuring Spark Plug Temperature

Types of Electrodes Center electrode Side electrode

Switching Devices Breaker points Electronic

Breaker Points Ran by cam shaft

Electronic Switching Devices NO breaker points to burn or wear out

The MBI Magneto System Mechanical Breaker Point Ignition produce power without an outside power source Condenser-prevents arching

The MBI Magneto Cycle Magnets pass legs

Coil 150 turns of large wire 20,000 turns of fine wire Iron core

The Stop Switch Plug only fires when points open Switch grounds points Fasten metal to head bold

Ignition Advance Systems Cause spark earlier BTDC As engine warms up Speeds up Centrifugal Vacuum Mechanical

Dwell & Cam Angles Time points stay closed Lobes size = dwell time

Electronic Ignition Solid state No maintenance No points-burning Spark plug life Easy starting Higher output Starts flooded engine Higher spark output

Electronic Ignition Hermetically sealed Uniform performance Good under adversity Improved idling Smoother power under load

Operation of Capacitive Discharge Ignition ( CDI) Solid State Newest NO Breaker points Magnets only moving parts

Operation of Transistor Controlled Ignition (TCI) Systems

Magneto Ignition Systems Compared

Battery Ignition Systems Low voltage primary circuit High voltage secondary circuit ignition switch builds field field collapses spark to plug

High Voltage Secondary Circuits Uses a step up transformer Several winding of wire / iron core

Auto-Transformer Type Ignition Coils

The Lead Acid Battery

Vehicle batteries