Topic: External Spark

[billstron]

I think this is probably a standard issue question, but I don't even know where to start with a search.  I have a '78 CB550.  I noticed the spark plug cap on #4 sparking to a screw on the head cover.  I moved the cap away from the screw and it stopped, but when I put my finger on it, I feel a shock.  WTF!?!?  What do I need to replace? 

[TwoTired]

The caps have a screw post where they twist into the ignition wire end.  Remove the cap and look at the wire end,  You should see a wire core and no goo.  You may have to trim a little bit off the end.  Whille the cap is off, measure the resistance form input to output.  If it is not within 5000 to 10000 ohms, replace it with a new one,m and screw it back onto the ignition wire.  Also, check your spark plugs.  They should have a number with no "R" in it.  If they do, then find yourself some NGK D7EA plugs to put in it.

The ignition fires two plugs at the same time.  The pairs are 1&4 and 2&3.  Check the mated pair's ignition wire and cap, too!

Also, on the cap to wire interface is supposed to be a rubber seal.  If yours is missing find a replacement.

Cheers,

[kettlesd]

First, make sure your plugs are the proper type, heat range and are gapped properly. To great a gap increases the power required to arc across, and increases the likelihood of grounding elsewhere.

Next, where on the cap is it arcing from? If its near the junction of the wire and the cap, then cut 1/4" off the wire and reattach the cap to see if there is a better connection (they just screw onto the wire). If its arcing further down the cap, then it must be replaced. If its actually arcing further UP the wire, then the wires must be replaced as a set. This normally entails replacing the coils too, as they are non-detachable - but some guys have devised ways of changing the wires only. Theres a good post in Tricks & Tips under "New Wires for Old Coils"

[billstron]

Thanks for the quick replies.  I will check your recommendations tomorrow after basketball.  Gotta watch the sweet 16.  Anyway...  A couple of things I know:  I am using NGK D7EA plugs.  Also the rubber boots at the top of the cap are in place, and they are the location of the spark.  It is pretty weird to see sparks coming from rubber, too.  Does that mean anything? 

A side note: If I need to replace the wires, has anyone tried plug wire splicers?  Here is a link to what I'm talking about:
http://www.z1enterprises.com/detail.aspx?ID=1890

Thanks again. 

[BobbyR]

Bill, run the bike in the dark if you can. This will allow you to see where that arc is coming from and also others that may be starting. If you think the caps are loose just snip a very small amount off the wire before you screw the them back on, this will give it a better bite on the wire. You clearly have a high voltage leak and that leak is before the spark plug. If your wires are shot, that splicer might be a good alternative.

[billstron]

I just (during half time of a game) ran my bike in the dark.  I couldn't see any sparks.  When I noticed them the other day, it was after it rained.  I still felt a very small shock with my finger on the cap. 

I will do more diagnostics in the morning. 

[billstron]

I just took the caps off for some testing.  #4 read 5.01k ohms and #1 read 4.89k ohms.  #1 looks a little low, could this cause a problem?  I did not notice any black gunk on the wire tips.  When I take the #4 cap off when while the bike is running, I can feel the spark through the wire.  Is this normal?  Any more thoughts? 

[kettlesd]

Sounds to me like  you need to replace the wires as a set. Read that post in Tricks & tips on how to put new wires into your existing coils.

[TwoTired]

I just took the caps off for some testing.  #4 read 5.01k ohms and #1 read 4.89k ohms.  #1 looks a little low, could this cause a problem? 

No.  You have 5 K ohm resistors and the tolerance is about 20% of rated value.  Your caps are good.  When they break down their value usually goes up.  They can even open, creating an internal spark gap that wastes energy.  Some caps are valued at 10K ohms. and others have been available at 7.5K ohms, though it has been a while since I've seen those.  You can get them with no resistors in side too, 0 ohms.
I asked you to check them because an open cap entices the spark to occur where not expected.

I did not notice any black gunk on the wire tips.  When I take the #4 cap off when while the bike is running, I can feel the spark through the wire.  Is this normal?  Any more thoughts? 

Yes. 1 and 4 fire simultaneously.  And, the current flows from one spark plug through the other.  It will use you as a path if you get in the way, or if you provide an easier path than the spark gap jump.

Are you still getting a spark jump to the engine?  If the spark is jumping through the wire insulation from the internal wire, then it is defective.  If it is traveling along the outside of the ignition wires, there may be some surface contamination providing an electrical path.  The last thing I can think of to try before replacing wires or rubber bits, is to clean them off with, alcohol, or MEK and let dry thoroughly.  You need a solvent that will clean contaminants, not leave a residue, and not dissolve the insulation.

Dust that has been used to pass an arc may leave behind a carbon trail.  Such a trail is conductive and provides a path for the electrical current.  You do NOT want anything conductive on the outside of the ignition wires.

Cheers,

[BobbyR]

You clearly have some leakage.  Since it was moist when you first noticed it is the tip off. The path may not be from the plug end of the wire, it could be travelling down from the coil end or anywhere in between. As TT said, wash them and seal them.     

[billstron]

I will try your cleaning suggestion as a temporary fix.  I think I want to replace the wires when I get a chance, though.