Evolution® Series Ignitions
What is the difference between EX
and race versions?
The new EX versions of our Models
1005-1007 have been given Air Resources Board Executive Order (ARB E.O.)
D-641-1. This makes these products exempt from the prohibitions of the
California Vehicle Code and 50 states street legal. The maximum spark advance
curves in the EX versions are more conservative, especially in the lower RPM range. The
figure below compares the maximum advance curves (advance slope set to 9) at
wide open throttle for the two versions.
The EX versions are suitable for
all street driven applications, including large displacement and high
compression engines where spark timing must be retarded from stock settings to
avoid destructive engine detonation. As a compliance criteria, the Air Resources
Board allows products such as the our EX versions to advance ignition timing up
to 4 degrees beyond the original equipment module. Thus the maximum advance
curve in the EX versions is still very aggressive and allows a performance
improvement when using 92-93 octane gasoline with stock engines.
The maximum advance curve for the race
versions are only suitable for true race engines where a long duration/high
overlap camshaft reduces cylinder pressure in the lower RPM range and high
octane race gasoline is used.
Both the EX and race versions of
our ignitions have sufficient advance adjustment range for most applications
using the advance slope switch settings. When used with our PC Link Evo
software, both the EX and race versions allow creating a custom advance curve
and no limitation exists on retarding the spark timing to solve a detonation
problem which is the most common reason for creating a custom curve.
What is the difference between
single fire and dual fire?
Single fire and dual fire refers
to the number of times the spark plug fires during each four stroke cycle. The
terminology is somewhat unique to Harley-Davidson® engines and is by no means
consistently applied. For example, Custom Chrome
Industries, one of the largest distributors of Harley-Davidson® aftermarket
parts, uses the opposite terminology. Their single fire systems correspond to
what most other companies refer to as dual fire.
With the exception of the new
Twin-Cam 88 and late model Sportster 1200 engines, all carbureted
Harley-Davidson® engines have been dual fire. A single coil winding with two high
voltage output terminals fires the spark plugs on both cylinders simultaneously.
Each plug is fired twice during each four stroke cycle. This approach was used
to cut costs as it eliminates the need for a distributor or a second coil and
additional electronics. Dual fire results in a number of potential problems.
Most late model automotive
engines are distributorless. Many of these engines use coil packs where a single
coil winding fires two spark plugs. When one spark plug fires on the compression
stroke the other spark plug is firing on the exhaust stroke. This approach is
termed "wasted spark" and is widely used. The wasted spark
always occurs on the exhaust stroke because the engines have even firing
intervals (i.e. 90° for a V8) and cylinders are always paired so that the
pistons are 360° out of phase (i.e. one on the compression stroke when the
other is on the exhaust stroke). The wasted spark causes little energy loss and
no harmful effect on the exhaust stroke.
The situation is quite
different with a dual fire ignition on a Harley-Davidson® V-twin engine with
315° and 405° firing intervals. The graphic below shows what occurs. When the rear cylinder is fired on the
compression stroke, the front cylinder is on the exhaust stroke - which is OK.
But when the front cylinder is fired on the compression stroke, the rear
cylinder is already on the intake stroke! Under some conditions, a combustible
mixture may exist in the rear cylinder at this point and the wasted spark
causes a backfire through the carburetor. Long duration camshafts and improper
carburetor jetting can contribute to the problem. Additional information on
this subject may be found on the
The Problem with
Dual Fire Ignition
A single fire ignition
eliminates the backfire problem and enhances idle quality. The single fire
ignition uses separate coil windings and electronics to fire each spark plug
independently. Spark firing occurs only on the compression stroke. Conversion
of older carbureted Harley-Davidson® engines to single fire is highly
recommended. There is no downside to single fire, other than the cost of the
Twin Tec Models 1005, 1006, and
1007 have switch selectable single and dual fire operating modes. You can
initially install one of our units and run in dual fire mode with your
original equipment coil. You can then easily upgrade to single fire by adding
an appropriate coil. If you have a tach, it will continue to operate properly
when connected to the tach output from the Twin Tec ignition (some competitive
systems require that you purchase a tach adapter).
What dual fire coil is
recommended for Twin Tec Model 1005, 1006, and 1007 ignitions?
If you read the section above,
you understand the drawbacks inherent with dual fire. Don't waste money on
another dual fire coil. Spend a few dollars more and buy a single fire coil.
All the Twin Tec ignitions for Evolution® and Shovelhead® engines have switch
selectable single fire mode, so all you need is a single fire coil.
What coil is recommended for
single fire conversion with Twin Tec Model 1005, 1006, and 1007 ignitions?
Single fire coils consist of
two independent coil sections combined together in one housing. The coil primary resistance should be in the 3 ohm range.
Make sure you don't buy a coil intended for Twin Cam 88® applications as these
have low .5 ohm primary resistance and will not work properly. Our part number
2005 coil is an excellent choice for use with all Twin Tec single fire
Single Fire Coil P/N 2005
Ignition coil manufacturing has
gone overseas to China. That is an economic reality we can't change. What we
can do differently is to be honest about it and pass the savings on to you.
Right now, one factory supplies Screaming Eagle® and
several of the aftermarket companies, including Crane and Dyna. Contrary to various claims, the coils are all
basically the same and just differ in cosmetics. Screaming Eagle®
31746-98A (black), 31748-98A (red), and 31750-98A (orange) have a bulky connector and may not fit some stock covers. Crane and
Dyna coils are packaged in a slightly smaller housing with conventional screw
terminals. We contracted with another factory to build a similar coil
What if I have dual spark plug
Twin Tec Model 1005,
1005S, 1006, or 1007 ignitions can be used in dual spark plug head
applications. Please refer to the
Spark Plug Tech Note
What is the VOES switch?
The VOES switch senses manifold
pressure. Most carbureted H-D®
models manufactured from 1980-98 and some later Sportsters®
use a VOES switch to increase ignition timing advance during idle and cruise
conditions. When manifold pressure (MAP) drops, the normally open VOES switch
closes and connects the ignition module's VOES input (violet/white wire) to
ground. The green VOES LED will illuminate. The ignition module then uses the
low MAP advance curve. If you look at the advance curves published in our
instructions, you will see that the low MAP curves are somewhat more
aggressive than the wide open throttle (WOT) curves. The additional advance
stabilizes the idle and improves cruise fuel economy. The VOES switch has no
effect on wide open throttle (WOT) operation.
During normal operation, the
green VOES LED should illuminate during idle. If you have installed a high
performance camshaft or made other major modifications, manifold pressure may
run higher at idle. In this case, the green VOES LED will not illuminate at
idle. You should still see the green VOES LED momentarily illuminate if you
rev the engine up to about 2,500 RPM and then close the throttle.
We recommend that you leave the
VOES switch connected. If you have a motorcycle where the VOES switch was
removed, we recommend that you replace it. We offer P/N
VOES-KIT-MC7. This is a complete kit with mounting bracket and has a vacuum
switching level of 6-7 in-Hg that helps eliminate spark knock under light load
or throttle roll-on.
Can I automatically retard timing
with a turbocharger or nitrous oxide injection system?
Yes! This is possible with Twin
Tec Model 1005, 1006, and 1007 ignitions. You will require the optional PC
link cable and software. You can easily reconfigure the VOES switch input as a
retard input. You can program the retard value over a 0-10° range. When the
retard input is grounded, ignition timing is automatically retarded.
For a turbocharger application,
you can simply replace the VOES switch with a pressure activated switch. For
nitrous applications, use a relay. Connect the relay coil in parallel with the
solenoid valves and use a normally open contact to ground the retard input
whenever the solenoid valves are energized.
For more detailed information,
please download our
Boost and Nitrous Timing Retard Tech Note.
Several competitors' internal
(nose cone) modules have failed on my engine. Will the Twin Tec Model 1005 be
It depends on the cause of the
failure. Besides obvious physical damage, the most common causes are excessive
temperature and over-voltage. If several modules have failed within a short
period of time, you have to step back and try to identify the underlying
cause. The following sections cover heat and over-voltage related failures.
Diagnosing and solving heat
Heat kills electronics. All the
major suppliers use the same type of electronic devices rated for operation at
105 deg C (221 deg F), the highest rating available. The Model 1005 can
tolerate somewhat higher temperatures, but exposure to temperatures above 125
deg C (257 deg F) will greatly reduce life expectancy. We sometimes see
problematic applications where several module failures have occurred. The
failure mode is a classic thermal intermittent where the module stops firing
one cylinder when it gets hot. We have found that these problematic
applications share one or more of the following characteristics:
VOES switch removed or non-functional. Without vacuum advance at idle and
part throttle, thermodynamic efficiency is reduced and engine temperatures
Improper carburetor jetting resulting in lean air/fuel ratio (AFR). A lean
AFR will cause the engine to run very hot. All performance engine
modifications necessitate carburetor rejetting. Carburetors are never
correctly jetted out-of-the-box. The only practical means of correctly
jetting a carburetor is to test the motorcycle on a chassis dyno equipped
with an exhaust gas sniffer or to use our WEGO system.
Lack of an oil cooler on a 95 CID or larger engine.
Exhaust pipe without heat shield in close proximity to nose cone.
Model 1005 units manufactured after January, 2006 include an internal
temperature sensor. These units log elapsed time in various temperature bands
up to 150 deg C. You can download this data with our Operating Statistics
You can easily diagnose potential
overheating problems by using an infrared thermometer to check the
module temperature. Remove the nose cone cover and place several strips of
black electrical tape on top of the module to provide a target for accurate
readings (infrared thermometers will not give accurate readings from
reflective surfaces). Operate the motorcycle for at least 20 minutes and take
an immediate reading after shutting off the engine.
Some high output engines may be
poor candidates for an internal ignition and an external module such as our
Model 1007 should be considered.
Extreme Over-Heating Damage
My engine runs too hot for an
internal ignition. How do I convert to an external module?
If you have a H-D®
model and the original wire harness is still intact, you can exchange your
failed ignition for our Model 1006 or Model 1007 external plug-in module as
appropriate for your application. You will also require the cam timing sensor.
If you no longer have it, you can purchase H-D®
P/N 32400-94 from your local dealer.
If you have a custom bike or your original ignition
harness has been removed, you can purchase
wiring harness kit H-D®
P/N 32408-90 and cam timing sensor H-D®
P/N 32400-94 from your local dealer and use these items along with our Model
1006 external plug-in module. The wire color codes are the same as shown in
our Model 1006 installation instructions. Please note that this wire harness
kit comes with a 7 terminal connector that will only mate with the
Model 1006, it cannot be used with the Model 1007.
We offer special discounted pricing for Model 1006
and Model 1007 units exchanged for failed internal ignitions, regardless of
the original manufacturer. Please call us at 386-304-0700 for details.
Diagnosing and solving
failures caused by electrical system over-voltage.
Failure from electrical system
over-voltage causes a surge absorber inside the Model 1005 to burn up. This
failure mode can be readily identified by a characteristic raised and burned
area on the back side of the unit as shown in the picture below and a strong
odor of burned electrical insulation.
common cause of this failure is momentary disconnection of the battery while
the engine is running. The system voltage then spikes up to a very high
level (over 30 volts) before the voltage regulator can react. It is not
unusual to also find other damaged electrical components, such as burned out
light bulbs or a dead radio on touring models. The problem is generally
caused by defective or loose battery cables, improper battery ground
connections, or internal defects in the battery. You must correct the
underlying problem before installing a new module, otherwise the same
failure will occur again. We suggest the following steps:
1. Replace the battery. Even new
batteries can have internal defects that cause an intermittent open
connection between cells
when the battery is
subjected to vibration or shock.
2. Replace all battery cables.
The battery negative
terminal must make a direct connection to frame ground. Some custom
motorcycles route the battery negative cable to the engine and then rely
on the engine mount to make a frame ground connection. This is never
3. Temporarily replace the
electronic ignition with a mechanical breaker point system. Breaker
points can withstand momentary
conditions without catastrophic failure. Make sure you use an
appropriate 5 ohm dual fire coil. Single fire or 3 ohm coils are not
compatible with breaker points.
4. Check the charging system. While not
the underlying cause, the voltage regulator may also have been damaged.
Verify that the battery voltage doesn't exceed 14.4 volts when the
engine is running in the 2,000-3,000 RPM range.
5. Operate the motorcycle for
several weeks. If no other electrical failures (such as a burned out
headlight) are noted, it is probably safe to install a new electronic
What is the proper orientation
for the timing rotor and Model 1005 ignition module?
This question sometimes comes
up in custom applications. The Model 1005 series (including the Model 1005S
EX) requires H-D®
P/N 32402-83 timing rotor. This timing rotor has two slots. The Model 1005
series cannot be made to work with any other type of timing rotor. The timing
rotor must rotate counterclockwise (CCW). The Model 1005 series cannot be made
to work in any applications where the timing rotor rotates clockwise. Correct
orientation of the timing rotor is shown in the figure below. This is a top
view showing an exploded Model 1005 for reference and the orientation of the
timing rotor with respect to the Hall Effect sensors when the engine is on top
dead center (TDC) on the front cylinder compression stroke.
Timing Rotor Orientation