SWM Electrics

Though I’d blown a couple of condensers on the 320TL, I’d but this down to problems with the loose connections on the wiring, but the Jumbo seems to have also developed the same habit.

When I’d originally got the Jumbo, one of the main problems was that electrically is was the proverbial dodo. At the time, in order to get a spark I’d swapped the stator plate and loom (probably a generous description for a simple wire and return) from the 1980 320TL. The wiring layout is different on the stators, with three wires on the Jumbo being connected to the condenser, this now being on the 320TL (but they are now swapped round).

SWM 320TL stator plate

The main problem was that Jumbo was now eating condensers, with two failing on the same day. Ok, the condenser is potentially the weak spot on the circuit, so rather than being a problem with the condensor its an indication that all is not well. The purpose (as far as I understand) of the condesor is to store (briefly) a charge and prevents arcing across the contacts, and burning the contact surfaces.

Jumbo stator plate

Ok, so looking at why the electrics were playing up, what are the potential causes ?
– loose connection. I blew a condenser on the 320TL on a Gwent Schoolboys trial and this was (I thought) because the earth lead from the ignition coil had come loose from the mount on the frame after one of the bolts had dropped out.
– problems with condenser(s) failing. The original condensers (that are soldered onto the wiring are much larger that the later condensers, but unlikely that all the condensers I’d had were not good.
– contacts, either the gap is too small or too large, or not properly prepared.
– poor wiring, there is a fault in the wiring, with a short somewhere
– ignition coil failing, could be breaking down as the bike heats up or problems with spark plug.
– bad or poor earth.

So the facts about the ignition system. I’m using NGK B5ES plugs (I’ve not checked the gap), contact breaker gap is 0.40mm and the bike is using the stock, original wiring. So, in a systematic attempt to prevent the world supply of SWM condensers being consumed during 2007, did the following work on the Jumbo:
– condenser: put in a old-style larger condenser (thats all I had in the workshop)
– changed the ignition coil. The one that came with the bike has seen some action (and some silicone sealant)
– checked the continuity, including the earth across the whole wiring loom. I find that doing continuity tests on the contact breaker to be very confusing (it never gives you the reading expect)
– cleaned the contact faces (they weren’t scorched) and reset the gap
– new B5ES plugs (from ebay for £1.20 each)

Also, then did the ignition timing with a strobe and set it to close to TDC (for now) and will adjust later. More reports on the electrical system to come, no doubt.

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