Lazy #3

Being an anorak, and knowing that old NGK caps are prone to fail, I bought some spares a very long time ago.
So a bit odd to find this 'new' one was faulty - first time I've had this problem.
 
Possibly a manufacturing fault, handling fault, possibly the cap had once fallen and the small and brittle resistor had got a crack.

You can saw it open and inspect the internals under a microscope.
 
Jouni obviously has technical skills, above the usual, well done. Am somewhat vexed that the problem stayed on number 3 after rotation between 1 and 3, provided i understand the written process evolved. Given it appears the problem stayed on 3 after number one spark plug cover was installed on 3, would indicate there may well be an intermittent fault or faults. Glad to be wrong of course. Not a clean cut solution to my reading.

Have had here on some motors the new iridium ( new to me that is ) with internal resistors going open circuit, most probable arc over on the resistor element, given most resistors are carbon film as opposed to the ancient carbon composition type, the former is a carbon film spiral cut and can be vulnerable to "valley" cut failure when the actual applied voltage is exceeded. That is no matter the actual resistance value, resistors have a maximum allowable applied voltage, with standing waves on an ignition system this "maximum working voltage" could be exceeded and resultant resistor operating outside its published rating, yes i know.... reads complex and is and not is..... a smile here. j.

**** FWIW, a low cost thermal image camera will indicate what exhaust header is under temperature, i used K type thermal couple secured to all three headers to "see" what the exhaust burn efficiency measured when tuning the carbies.
 
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You're right John, the lazy cylinder #3 continued - or seemed to - unaffected by swapping leads over between 1&3, complete with the attached faulty cap.

Having said that, this was all during pre Christmas testing and my grey cells are getting ever more forgetful with age! Had to remind myself which cylinder is No 1 when I came to write my first post... 🙄
 
I'm not surprised at all of this behaviour of the problem, not moving from pot to another when changing leads. Especially after when everything was setup again, there is at least a small difference on mixtures and pressures in the cylinders. If the engine was just rebuilt, the sealing of the piston rings will become soon better, and the carbs need to be tuned a couple of times before the rings are fully settled. Also the pickup will become better and more even for the carburettors. Sometimes after a rebuild the condition can be quite close for a while that it is even running. Can be also that something is a bit different on #3 carb for example. Eventually there probably was a weaker spark on both cylinders because of the fault in one cap, but just the another pot went over the limit not to run.

Laverda has numbered the cylinders that #1 is at left, #2 at center, and #3 at right. European standard used to be that the numbering starts from the opposite end of the crankshaft than the drive end, that would be just the opposite. Not surprised that the numbers of pot #1 and #3 are often confused.
 
The sole function of the resistor element, be it plug cover or incorporated into the actual spark plug, is to reduce rapid voltage ( and current ostensibly ) rise slope, this rise can and does cause broadband electrical interference. You can actually run an ignition without suppressor resistors though points only as a rule. Electronics can be well effected by a non suppressed ignition system. HTH j
 
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