Plug cap specs

The other evening I was going through the ignition system with a fine tooth comb as the 650B was idling rough and the timing light showed 2/3 jumping all over the place. After measuring everything and everything checking within spec (stock coils, points, etc.) I put the ohmmeter to the plug caps and found both to be open! I pulled the 2/3 coil off the parts bike and measured those caps and they turned out to be nominally 5000 ohms. Last night I checked the 1/4 caps and they also measured nominally 5000 ohms.

Unfortunately, even the factory service manual gives no spec for them. On another forum it was suggested that the NGK caps were 5 ohms! So, I got the part number off of Z1 Enterprises for the NGK cap that most closely matches the KZ650 ones, LB05F, and then did a bit of Google searching.

I found this page on the XS11 owners forum which shows a catalog scan with the part number legend. The new caps are available in either 5000 or 10,000 ohm versions, so I presume the stock caps should also be about 5000 ohms.

Hopefully, that reference will help someone else trying to track down an ignition problem. From now on, those caps will be one of the first things I suggest someone check when troubleshooting ingnition problems.

- Nate >>

Why would the bad plug cap cause the timing to jump all over the place? Just curious.

N0NB wrote:

and the timing light showed 2/3 jumping all over the place.

It probably doesn't at least directly. However, I was seeing a lot of sparking of the points before I changed them and that is gone now. The engine RPM was surging and while that isn't totally gone, it is quite a bit less. And the 2/3 timing is still not as stable as 1/4. I filed and cleaned the points, but it's possible the points and/or the condensor just aren't right. I think a Dyna S is in its future and maybe more.

It is good enough now that I rode it around the block a couple of times this evening (my first ride on it, actually) and it pulls well. I feel comfortable getting it titled and registered now and continuing on.

- Nate >>

I had a sort of similar issue last year and found some of my plug caps showed open circuit.

Also found that even NGK plug caps with 5000 Ohm written on the pack may actually be 1000 ohm (stamped on the cap itself

Found my original posting in the archives. See kzrider.com/forum/viewthread.php?tid=26782 which developed into an interesting thread. IMHO