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| The Sky (or light) Blue wire is another wire that connects to the CDI. It
connects the neutral detect switch (electrical sensor just behind the shift
lever) to the CDI. The light blue wire is grounded by the switch when the
transmission is in neutral. It changes the rev limiter to 7,500 RPM and reduces the
voltage to the spark when the transmission is in neutral. Disconnecting the
switch allows this circuit to remain high, due to an internal pull-up resistor,
regardless of transmission gear position. This causes the engine control unit
(ECU) to default to the in-gear position. TT member McGrath analyzed the
function of the neutral switch and blue wire. The data is provided in the
graphic below.
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Observations from data:
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Below ~2000 rpm both the in-gear and neutral spark surfaces are the same so
this mod will NOT effect engine performance in this range.
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Above ~2500 rpm the spark surface is much steeper in gear than in neutral
both as a function of engine speed (see Figure1) as well as throttle position
(data not presented). Just for reference, a moderate kick will get you about
1000 rpm which will then double at the very first combustion event.
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Benefit
I have seen the claims for improved starting with this mod and they
appear to be backed up by the data. That is, DEPENDING on how fast you spin the
engine while kicking it and how high your idle is set (a strong kick and a high
idle speed will enhance the performance of this mod). The more advanced spark
from the in-gear spark surface will tend to give a stronger run-up than the
neutral spark surface. Others have claimed this mod will also improve spark plug
life. This has not been proven.
Risk
The engine idle speed in neutral may tend to be somewhat unstable (i.e.
hang-up, oscillate or mimic a fuel lean idle condition) simply because of spark
advance. Do not flog the carburetor to death for this condition.
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Remove the seat, radiator shrouds, and gas tank.
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Locate the CDI (black box on the right side of the steering stem)
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Trace the wires from the CDI unit. Find the six-wire loom with the sky blue wire in the corner (Figure 1). Unplug.
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You DON’T cut the wire you simply unhook it. Use a small screwdriver to pull the dust ring around the wire from the back
of the connector.
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From the front of the connector use the small screwdriver to
release the tab holding the wire in place and pull the wire from the back of the
connector (Figure 2).
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Plug in the connector
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Tape the removed wire to the outside of the connector with
electrical tape.
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Reinstall the tank, seat, and shrouds.
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Figure 1 |
Figure 2 |
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Click on images to enlarge |
Alternatively, you can remove the
entire neutral switch harness and plate since the only wire that is connected to
the CDI from the neutral switch is the sky blue wire. Zip-Ty racing makes a
neutral cover replacement for $14.95 that bolts on to the tranny to cover the
hole left behind when you remove the neutral switch (figures 3 and 4). Most
people also remove the spring and the pin from inside the cavity although it is
not entirely necessary. |
Figure 3 |
Figure 4 |
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Click on images to enlarge
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Update for 2003-2004 Model |
On the 03/04 models, there is a dark blue wire and a sky blue wire
running from the neutral switch to a plug with a single sky blue wire on the
other end that goes to the CDI. If you unplug this connector there's no need to
disconnect the sky blue wire from the six wire harness. Also, on the 03/04
models, the WR250F will not e-start without the clutch disengaged after you
unplug the neutral switch wires. That's because the WRFs have dual safety
mechanisms to prevent you from engaging the starter with the bike in gear and
clutch engaged (the neutral switch and a dead man switch on the clutch). The
bike either has to be in neutral or the clutch disengaged to e-start. By
disconnecting the neutral switch harness, the system thinks it's always in gear.
You can still e-start, you will just have to pull in the clutch lever even when
the transmission is in neutral. Another option is to jumper the two wires from
the dead man switch together which will lwt the starter think the clutch is
always disengaged. |
ThumperTalk Archives
(updated by TT member learning2fly 01/14/05) |
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Listed here are what
I consider the most helpful threads. There are more threads on this topic in the ThumperTalk archives. To find them,
search the
YZ250F/WR250F forum. Suggested keywords: nuetral switch, Zip
Ty, blue wire, sky blue wire, free mods, free modifications. |
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