Topic: Odd issue- no spark except when....

[mikedialect]

Ok, having an odd problem. I'm not getting any spark on the left cylinder. 1972 cb350 k4 twin.

So, far I've:

Switched plugs
Cut coil wire down and remounted cap
Checked wire connections
Basically chased my tail

Also, I've gone through the entire tune up process. New points, timing, carb rebuild, new lines & filters, oil, etc. I know that doesn't matter much, but I've reached this point with....

...the odd thing. When checking for spark I only got spark from the wire with the cap removed or from the plug when I was turning the kill switch into the off position. Any ideas?

[Aaron J Williams]

Ok, i'll take a stab at it. If you have spark from the wire but not through the cap then maybe the cap is bad, possibly burnt open inside the cap. Try switching caps from side to side or replace with a known good cap.
If you get a spark when turning the kill switch off that would suggest that the path to ground through the points is not happening but the kill switch completes the path to ground and causes the coil to discharge. Ohm the wire between the coil and points looking for an open circuit.  Hope that helps!

[mikedialect]

well, I asked on hondatwins.com as well and I found my answer!

Mike, You obviously have a "glitch in the wiring to the coil(s).... A coil fires (discharges) when the current to it breaks, and you are "breaking" the current by opening the contacts in the kill switch..( I presume a stock Honda "kill" switch)...This means, that the "ground side of the circuit is NOT breaking which usually means a point wire is shorted to ground even when the point opens..... Check the Yellow or Blue wire from the coil to the point (whichever color goes to the non-firing coil).... it is likely shorted where it goes through the housing to the points, or at the point where it bolts on.... If the wire is spun and touching the plate, or those little (usually brown) insulators are cracked or missing....There you are! It can also be shorted indirectly by the capacitor (condenser) wire of the same color
I have seen the symptoms disappear when the point cover is removed...This just means it was shorting to the inside of the cover (dented cover or no gasket)....
Fix the short to ground and it will work properly..... Steve

he was 100% dead on!

problem solved and the twin is back in business