OZ ATV :: The Australian ATV Forum

[Arnie450]

I have a YFZ 450 that is miss firing at high revs under load. It is like the revlimiter is cutting in at 6-7000 revs. I have cleaned the fuel system and changed the fuel. I have also changed the spark plug. None of this has helped. The battery has also gone flat. I dont know if they are related. I have charged the battery, and will check the charging voltage.

Any ideas

Arnie450

[JONO]

hopefully this helps:
http://www.ozatv.com/forum/viewtopic.php?t=12407

[Clarkie]

Chuck it on the trailer and get ya arse up here for speedway this weekend and i'll fix it on saturday for you.
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[Clarkie]

Check the plugs under the front cowling for corosion etc..., how is your vapor speedo hooked up?, hard wired into the ign system or wraped around the coil? Try disconecting that and see what happens, had a few play up, change your Iriduim plug also cos ive seen them brake down under high RPM, if all that fails give us a call or refer to previous post.
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[bigjon]

Mine had the exact same problem. If your battery is not completely rooted, appease me and charge it then ride with your lights ON.

Below might explain your issue.
________________________________________________________

The YFZ450 Charging System is designed to
supply at low to medium engine rpm a maximum
charging rate with the headlights in the
ON position. Under some conditions (e.g., low
speed with cooling fan running frequently or
continuous high rpm riding), it may be necessary
to ride with the headlights in the ON position
continuously to maintain a fully charged
battery.
If a customer complains of the battery discharging
while riding, first check the condition
of the battery.
NOTE: If improperly charged or boost charged,
these compact batteries could overheat and
become permanently damaged. To prevent
overheating, charge the battery using a low
output charger (e.g., Optimate III, ACCOPTIM-
AT-E3), and test the battery to make
sure it is in good condition. Next, Check the
output of the charging system.
To avoid mis-diagnosis, follow these procedures
and specifications in the order below:
1. Minimum key off (battery voltage must be
12.80 VDC).
• Voltage too low: recharge and load test
the battery.
2. Measure the battery voltage at idle. *It
should be 14.0 ~ 14.9 VDC before the cooling
fan starts to cycle ON and OFF.
• Voltage too low: check the stator coil
resistance. The correct specifications
are:
– Yellow to Ground = 0.22 ~ 0.60 ohms
– White to Ground = 0.29 ~ 0.84 ohms
– Out of Spec: replace stator assembly
• Voltage is too high: check wire continuity
(particularly the black wire which
should have continuity between the
Ground). The Yellow/Red wire should
have continuity between the lighting
coil and the regulator.
NOTE: If continuity checks good, replace the
regulator assembly. (Commonly, both headlights
are burned if the regulator has failed.)
• Voltage Okay:
–
–
–
NOTE: Do not check the battery voltage at
5000 rpm as explained in the Service Manual.
Charging output will decrease as rpm increases.
This is a normal characteristic of this
model.
*Since the system normally discharges anytime
the cooling fan is ON, all testing must be
done before the fan starts to cycle on and off.
Otherwise, the maximum measurable battery
voltage will be lower than 14.0 VDC.
SUBJECTS: 1. Unique Charging System Characteristics - YFZ450
2. Introducing YFZ450 Charging System Resistor Kit -
Resistor Kit for Competition Usage
3. YFZ450 Resistor Kit Installation Instructions

Check the radiator for blockage and
correct as required.
Advise the customer to use the key
switch to turn the engine off. Only
use the engine switch (on the handle
bar) in an emergency.
Advise the customer to switch the
headlights ON to increase the charging
output.
Introducing YFZ450 Charging System Resistor Kit -
Resistor Kit for Competition Usage
Symptom:
As explained in the previous subject (page 1),
the YFZ450 Charging System is designed to
supply at low to medium engine rpm a maximum
charging rate with the headlights
switched to the ON position. If the headlights
are removed for competition use, the unit may
experience battery discharging.
Remedy:
Install the YFZ450 Resistor Kit. The kit contains
a ceramic resistor which takes the place
of the headlights to maximize the charging
rate, plus it provides a higher temperature fan
thermoswitch to minimize current draw. The switch is
located sitting on the bike the upper right switch
NOTE: This higher temperature is still low
enough to not cause engine overheating.
The kit is optional for competition use and warranty
does not apply. The kit was developed to
allow maximum charging and reduce battery
load.
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Don't close your eyes during the crash, you'll miss the best part

[Clarkie]

Some good info there Bigjon
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[Arnie450]

I have found the problem. The stator had come loose and is now in many pieces. The thread in the magneto cover has been torn out. Bit nasty.

Thank you to all for your advice. I wouldnt have started trying to find the issue without your leads.

Cheers

Arnie