Japanese Coil Question-Resistance

What is the typical resistance in the primary winding of a coil for a
Japenese bike? I think that the coils on my '75 Honda 400 F are bad but
do not know this value. Is it in the ohms range or is it kilo/mega ohms?

PJ

 

Thanks for the info. I probably should have asked about the secondary
resistance because the bike that I have (a Honda 400 F) has no spark in
either of its coils. I hot wired 12v straight to the primaries and still no
spark.

PJ

 

<blink><blink>

For the coils I'm used to, a constant 12v DC shouldn't show
anything on the output beyond a flicker at the initial connection. Coils
are basically just transformers, which require a varying
current/voltage. Oh, and did you have a capacitor in the system? You
might need one to get a high-enough current level to see a resultant
spark.

{fixed pitch font needed}


out-a ------ -------/ ------+------- in-a
)( switch |
coil )( _ capacitor
)( _
)( |
out-b ------ ---------------+------- in-b

A momentary contact switch should let you keep tapping it and, ideally,
you'd get an output spike as the capacitor discharges on each press.

--

 

You have to be careful what you're measuring.
There's often a resistor in the plug cap, so you may have to remove it
to measure secondary resistance. 10s of KOhms.
One failure mode is for there to be an arc between turns. This destroys
the tiny wire, but there's enough voltage to bridge the gap, so it still
works...until it destroys another turn which increases the gap and so
on until the internal arc is too big to sustain the arc in the plug.
For the modern CD ignition, it dosn't take much to start this process.
If you turn it over with the plug wire removed, there's huge voltage
inside the coil that can start the breakdown. Once it starts, it's just
a matter of time.

I had a Honda Shadow that was arcing from the middle of the coil to the
radiator. Put a piece of plastic between and gooped it up with
insulation. Ran it another 50K miles before I had to change the coil.
First two coils I got from the junk yard had open secondaries.
Take an ohm meter with you when you buy a used coil.
mike

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Well, I'll confess I hadn't been looking at it from the point of
view of a full distributor. The above was meant to be a test rig -- the
switch would have been a manual control, and the capacitor would ensure
enough current to get something out the other end <G>

--

 

Actually the capacitor goes on the other side of the switch to prevent

*boggles*