nighthawk 550 electrical problem

Krusty,

My suspicions are confirmed. I waited a couple of hours an
went out and pulled the cover to inspect the pulse generator. There wa
some corrosion around where that bad pickup bolted in. I cleaned tha
area up good and tested the resistance and it was in specs. I figure
problem solved but found out while riding that as soon as the bik
heated up good the problem (running rough and missing) returned. Sur
enough upon testing the resistance on the two pickups the same one wa
bad. Any thoughts you have on this are greatly appreciated.

Jef

 

Well, that explains mysterious intermittent rough running.

The pulser coils wouldn't be grounded to the frame, both wires would go
to the ignition control module. As the rotor on the right hand end of
the crankshaft passes each pulser coil, a short pulse goes to the
ignition unit. It's only about 2 volts, but that's enough to trigger
TWO spark plugs to fire. The engine fires TWO cylinders each time a
pulser coil makes a spark, but only one of the two sparks is useful,
the spark that's occuring while the exhaust valve is open is called a
"waste" spark.

The pairs of cylinders fired are 1 and 4, then 3 and 2, since the
pistons are on opposite strokes 180 degrees apart. You should be able
to tell which cylinders aren't firing by looking at the spark plugs. A
cylinder that's not firing will have black sooty spark plugs.

If one pulser coil is opening up when it gets hot, you can check to see
if
there's a problem in the connectors and wiring, you can even pull on
wires to see if the insulation stretches out. That indicates a broken
wire inside the insulation. If you can't find anything external, the
open circuit is inside the pulser coil itself.

If you can get the pulser coil problem fixed and the engine runs
smoothly so it will rev up to 5000 to 7000 RPM you can do the open
circuit voltage test again. The 1 volt that you got wasn't impressive.
I suggest that when you get the engine to run on all four cylinders,
remove the alternator cover so you can see the cooling fan. If it
doesn't turn when the engine is running, then the alternator cannot
generate AC current.

The CB-650 Nighthawks had an excited field alternator with brushes.
There was no cooling fan, you would spot that right away, and you'd be
able to see the brushes. The voltage regulator sends battery voltage
through the brushes into the rotor, making an electromagnetic field.
When the rotor turns, that's what makes the voltage.

A permanent magnet alternator, OTOH, has very strong permanent magnets
that induce the electricity in the stator. But the rotor absolutely
must *turn* when the engine is running to generate electricity!