Motorcycle Repair: 2 of 4 cylinders not running, honda cb750k, maintenance challenges

Question
'79 Honda CB750K. Bought used, and needs work. I got it to
start, let it run for a couple minutes, but noticed that cylinders 3
and 4 are not running (exhaust headers cool to touch - 1 & 2
burned my hand-DUH!). I believe this model takes 2 igniters - 1
for each pair of cylinders. How should I test to see if that's the
problem, or what other suggestions would you offer? I have
good used coils coming, and will check plugs also.

Answer
Hi Chris,

Are the ignitors leaking? They are prone to getting hot and melting the material on the undersides. When this happens, they soon stop working.

Is the battery in good condition and fully charged?

Check output voltage from the alternator. Connect a multimeter to the battery terminals and measure charging voltage. Expect to see between 13.5 VDC and 17 VDC.

Respectfully,
Mark Shively


(tech notes)

It sounds to me like you are describing the Spark ignitors. I've
heard of people that keep riding for months after they start leaking
and just clean up the mess until the quit. I think if it was me I'd
go ahead and replace them, they are obviously overheating and causing
the sealer to get hot and melt.
Check out Ray's Honda Board for more info:
http://clubs.yahoo.com/clubs/rayscbdohchondaboard
good luck and ride safe
jdj
J.D. Johnson
'83 CB750SC (for sale maybe)
'96 Royal Star
Homestead Florida


--- In cb-750@y..., Robert Johnson <rejohnson1@y...> wrote:
> My least favorite part of most of the motorcycles I've
> owned has been the electrical system. Naturally,
> that's where most of my maintenance challenges occur.
> Here is another one. I'm getting a very late start on
> riding this year, finally getting the 1981 CB750C out
> and beginning to set it up yesterday.
>
> When I took the battery out I found some tar-like
> substance on a corner. Thought at first it was the
> case going bad, but then I could see it dropped onto
> the battery from above. Turns out that there are 2
> mystery electrical components above the battery. From
> the top they look like aluminum heat sink cases, but
> when you peer up from underneath the bottoms are open
> and they are filled with this tar-like substance. I
> think its called "potted" circuits where this stuff is
> poured over the things to make sure they don't
> vibrate.
>
> So clearly at some point last year these things got
> hot enough to melt the tar, and several drops of it
> fell down into the battery compartment. Both of them
> have areas which look like pending drops that
> re-froze.
>
> The two devices are marked "Oki" and "MPS 200". But I
> don't know what they are. I think they might be part
> of the spark system, but my Clymer manual is vague and
> the pictures are too murky to tell where the wires are
> headed.
>
> This morning I went to the nearest repair shop and was
> informed that they won't bother to work on or talk
> about anything more than 10 years old (helpful, eh?).
>
>
> 1. Can somebody tell me what they are?
>
> 2. If I blindly replace them, what are the odds that
> the real problem is elsewhere and I'll ruin the new
> ones?