nighthawk 550 electrical problem

Krusty,

I just checked the resistance on the three yellow leads fro
the stator again and this time put the setting on the lowest setting
Once I did this the resistance measured .5 on all three leads. Maybe i
is a bad connection. But where? The symptoms are strange in that th
bike is erratic. Once it warms up it will run good and allow you to re
the engine above 2000 rpm. Before it is warmed you cannot exceed 200
rpms. The funny thing is that after riding it for a few minutes it goe
back to the way it runs when cold. I am stumped. I have checked ever
ground and they all seem well connected and clean

 

Well, if you can test the stator resistance by getting on the pins in
the plug that goes to the rectifier regulator unit, then use your
ohmmeter to check for continuity from the DC plug to the wire that
hooks to the battery. Disconnect it from the battery, of course.

0.5 ohms phase to phase sounds more in line with what I expected. Try
the open circuit voltage test, look for around 80 to 120 volts AC
between all of the yellow wires while the engine is running around 5000
RPM.

If you have that much AC voltage on the open circuit test, the stator
is OK, and the problem is the voltage regulating circuit in the
rectifier regulator. Better that it should be the RR that costs around
$125 than it should be the stator that costs $275...

If you have continuity through the stator wires, but you don't have
open circuit voltage that would indicate that the alternator rotor
wasn't turning. I've seen that happen just twice on different
motorcycles. The rotor wasn't not turning when the crankshaft was
turning because the nut holding it on was loose.

That could be electrical or dirty carburetors. Or both...

Is the poor running with a fully charged battery, or with an almost
dead battery? If the voltage from the battery is really low, there
might not be enough voltage at the spark plugs to fire a lean mixture
from the carburetors.

Since the early 1980's, the EPA has required the motorcycle
manufacturers to set the idle mixture very lean, and that does not work
well with a weak ignition system that doesn't put out very much voltage
at the spark plug gap.

I looked at the parts fiches for your Nighthawk at www.partsfish.com
(if you go there and register, you can look at parts diagrams for free)
and I can see the ignition control module and the pulser coils. From
what I can tell, it's just an ordinary transistorized ignition module,
not one of Honda's so-called "CDI" ignitions. Honda's CDI ignitions
have a special high voltage coil in the alternator stator that puts out
around 100 volts so the ignition coils get a sudden high voltage shot
of DC electricity when the pulser coils signal that it's time to fire
the plug.

You can tell if an ignition system is just a transistor ignition system
if you put your voltmeter probe across the positive terminal of the
coil with the ignition key turned on. You'll have 12 volts. If it's a
CDI system, you won't have 12 volts. But you'll get 50 to 100 volts on
the positive terminal of the ignition coil when you crank the engine
with the starter.

It's possible that your idle jets are plugged up from storage and the
idle mixture ports controlled by the idle mixture screws may be dirty
aggravating the cold running with low voltage. I have explained about a
bazillion times how to clean out the idle jets and the idle mixture
passages. If you want to review all of the explanations, you can do a
google search for "idle jet" on rec.motorcycle.tech and you'll find it.