Hi Kurt, Kyle,
Thanks for the advice.
To clarify, I am referring to the key switch (it's labelled "ignition
switch" in Clymer's wiring diagram). And yes, I've already taken out the
key lock/switch assembly, tried to order a replacement for the electrical
component ("Base Contact", Honda part #35101-MBV-003), and been told Honda
has discontinued the part. From your pictures, Kyle, it looks like the
90's switches are different from the 80's model.
Grounding seems like another good check. The path from plugs to battery
negative was fine... I'll have to pull the tank again to check the coils.
Or should I check (also) ground at the ignition control module? I'm a
little confused about the ignition control module, actually. From the
wiring diagram, it looks like the ignition coils' primary wiring is
grounded through the ignition control module and takes positive from the
battery through the engine stop (kill) switch. However, I thought that (1)
the bike had capacitor discharge ignition (CDI) and (2) ignition coils
using CDI took primary coil positive from the ignition control module
(where the charged capacitor lives) and primary coil negative was directly
grounded. What am I missing?
Unfortunately, I can't tell which cylinder or pair is misfiring, so I'm not
sure how to track down an issue with the coils themselves, beyond measuring
primary/secondary resistance (which I ought to do...).
Relay mods for coils, etc. are something I've thought about doing. I guess
I need to correct my about confusion of ignition control before attempting
that. The high resistance at the key/ignition switch seems like an
elephant in the room, though, since that's effecting every circuit on the
bike.
Cheers,
-ntd
On Thursday, February 25, 2016 at 3:48:35 PM UTC-6, Kyle Munz wrote:
>
> I can't say if it is the switch off of that information, and I have no
> idea how similar the '90s switch is to the '80s switches, but I took pics
> when I rebuilt mine (http://nighthawk.kylemunz.com/?p=600). It's
> definitely serviceable and I've seen those fail due to vibration which
> caused intermittent stumbling going down the road and mimicked a misfire.
>
> Also, Kurt is right, could be the grounds or the coils themselves (even
> the ones you swapped in). Each coil supplies two cylinders, if you can tell
> which one is misfiring swap the coils and see if the problem follows the
> coil or stays where it was. Some coils will test fine on the bench but fail
> when heated up.
>
>
> -Kyle
>
> On Thu, Feb 25, 2016 at 3:40 PM, Kurt Nolte <[email protected]
> <javascript:>> wrote:
>
>> The ignition switch (do you mean key, starter, or kill switch?) isn't a
>> sealed unit.
>>
>> If you mean key switch, you can replace the electrical part independently
>> of the key switch. You have to remove the headlight bucket and the cluster
>> to get to it, then it's just three small Torx screws.
>>
>> Another check is grounds. Check your coil grounds, and check the ground
>> strap from engine to frame. Grounding issues are a huge player in vehicular
>> gremlin attacks.
>>
>> Coil relays are a good mod, and incredibly reliable if you buy a sealed,
>> automotive grade relay of the right size. I've run a 40A Panasonic CA
>> series relay for my '93 Nighthawk's coils for three years now, with no
>> issues and a MUCH lower resistance path to the coils. I used another pair
>> for the headlight hi/lo, and a fourth for the horn, all much better
>> performing for it.
>>
>> Kurt
>> On Feb 25, 2016 4:07 PM, "Neil Dantam" <[email protected] <javascript:>>
>> wrote:
>>
>>> Dear Armchair Electricians,
>>>
>>> The problem
>>> ===========
>>>
>>> My '97 CB750 developed a misfire a few weeks ago. The problem
>>> would only happen after the bike was warmed up. Pulling the plugs
>>> didn't reveal a smoking gun (to me at least, photo attached), and
>>> swapping in different ignition coils made little difference. However,
>>> I measured resistance across my ignition switch at 3.6 ohms, and
>>> bypassing the switch (I guess that means hotwiring the bike) fixed the
>>> misfire, though warmup is still a bit sluggish. I take this to mean
>>> that accumulated resistance in the switches and harness are dropping
>>> voltage enough to cause loss of spark. Any other potential causes
>>> that should be considered?
>>>
>>> The other problem
>>> =================
>>>
>>> The easy answer would be to clean the ignition switch, but AFAICT,
>>> it's a sealed unit. The next easy answer would be to replace the
>>> switch, but Honda has discontinued the part. So, now one must be
>>> creative.
>>>
>>> Solutions
>>> =========
>>>
>>> Here are the potential solutions I've come up with:
>>>
>>> 1. Find a used switch on ebay/junkyards and hope it's good
>>> 2. Forcibly open the switch (or an ebayed-replacement), clean up it,
>>> and get all the king's men to put it back together again.
>>> 3. Get an aftermarket ignition switch (though I really don't want
>>> another key)
>>> 4. Use the existing switch to drive a relay for main power
>>>
>>> I am inclined to try options 1/2 and 4. 1/2 depends on finding and/or
>>> modifying a Honda switch, which may or may not work out. Driving a
>>> relay using the existing, degraded switch should work OK since relay
>>> coil resistance is ~100 ohms. It does create a central point of
>>> failure, and relays are not the most reliable components. (maybe
>>> redundant relays are the answer?)
>>>
>>> Does anyone have a different interpretation or solution for this
>>> problem?
>>>
>>> Thank you and happy crimping,
>>> -ntd
>>>
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