S&S Cycle IST Ignition System for 1984–99 4 1/8 Bore Big Twin Engines - Manual (Page 2)

Instruction Contents:
A. Introduction
B. Parts List
C. Removal of Existing Ignition Module
D. S&S® System Installation
E. Initial Starting and Operation Procedure
F. Basic Troubleshooting
G. Advanced Troubleshooting
Do not use a dual fire coil with the S&S ignition module.
This kit will NOT work with vehicles equipped with flat slide carbs, open primaries, and dry clutches. If you want to use IST with these
configurations contact S&S, we can help set up IST.
A. Introduction
The Intelligent Spark Technology system uses a sophisticated computerized module that integrates data from sensors that other ignition
systems are not designed to use. The S&S system makes use of crank position sensor, cam position sensor (if present), MAP sensor, cylinder head
temperature sensor, and an exclusive knock sensor that actually detects detonation or knock while the engine runs. The knock sensor allows
the IST to automatically adjust ignition timing to eliminate knock whenever it occurs. In addition, the system “remembers” the conditions that
cause the engine to knock and automatically adjusts ignition timing to prevent it when those conditions reoccur. On the other hand, when
conditions allow for increased ignition timing, the system will advance timing as far as possible without causing the engine to knock. In effect,
the system “learns” the ignition requirements of a particular engine and writes a custom ignition map for it.
If ignition requirements change, if a lower grade of fuel is introduced, for example, the system will automatically make the necessary ignition
timing changes to avoid detonation and possible engine damage. This feature is particularly important in touring applications where the rider
sometimes has less control over fuel quality. If a different camshaft is installed, or if cylinder head modifications are made, the S&S Intelligent
Spark Technology system changes the ignition timing for the new configuration. Even if major engine modifications are made, such as the
installation of a stroker or big bore kit, the system will adjust to the ignition requirements of the engine.
Additional features:
• Simple installation — installation kits plug into stock wiring harness.
• No timing adjustments — the system adjusts timing automatically.
• Factory pre-set 6250 RPM rev limiter. Adjustable up to 7200 RPM with S&S IST Guardian Diagnostic System (p/n 55-5075).
• Single fire operation — requires two coils or dual coil package.
• High output — Automatically maximizes coil output.
• Automatic dwell adjust — will optimize current for any coil 0.5 to 3 ohms.
• Short circuit and reverse polarity protected.
• Diagnostics — Guardian Diagnostic System or harness jumper.
NOTE: The electronics used in the S&S Ignition System require operation in single fire mode only. The S&S Ignition System cannot be used in dual fire mode.
Dual Fire vs. Single Fire Ignition Systems
Two Types of ignition systems have been used on Harley- Davidson® motorcycles, either dual fire, or single fire.
Dual Fire
Dual fire ignitions fire the spark plugs in both cylinders on every stroke, each time the pistons reach the tops of the cylinders. One piston is at
the top of the compression stroke, while the other piston is near the top of the exhaust stroke. Dual fire is also known as “wasted spark” because
the second spark fires near the top of the exhaust stroke. Dual fire was common for many years because of its simplicity and reliability. Dual
fire has a slightly rougher idle than single fire because the “wasted” spark occurred just after the top of the exhaust stroke of the rear cylinder,
disrupting the incoming intake charge.
Single Fire
Single fire ignitions fire the spark plugs on every other stroke of the engine, only at the top of the compression stroke. One cylinder fires, then
after one crankshaft revolution, the other cylinder fires. A single fire ignition system allows the ignition to reliably transmit more power to the
coil during the compression stroke when it is needed most.
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CAUTION