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Strange coil faults and sparking???

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Laverdaroo:
Hi after a good fiddle at the weekend (leave it Phil), and a tuning sesh getting the 400 sorted for the Boss, I turned to getting the 550 running a bit better. It's timed spot on, both statically and when running last weekend on 4 pots, done dynamically with good results. Valves done,carbs balanced, again last weekend when it was on all 4, and although kinda set up, needs finisheing off hence the twiddling yesterday.

I set everything up and it started with barely a touch of the button but only on 3 (2,3,4). Ok, pipe one cold, all other pipes nice and hot and all sparking with a test plug in each HT cap in turn when touching the head with the bare plug end, as you do.

So I have 2,3 and 4 all doing good and spot on so I take the plug out of cyl 1 and touch it against the head and press the starter.......nothing!          That is until I move the plug away from the head by about an inch and get a big long blue spark??? I number all my plugs with a marker to keep diagnosis easier should anything like this arise so I tried another plug and the same result, interesting!  Everytjing else behaving as they should and showing fat sparks on the head when touched while hitting the starter.

I then go accross all four HT leads doing the same thing and all are fine except when trying number 1 which then promoted the 'obligatory' wiggling of wires and leads to try to see how intermittant and where the fault might be coming from. Same results.

Went for a brew and a thunk after a small consise Anglo Saxon retort, as expected!

Went back out 10 mins later and preceded to do it all again except this time all four plugs were doing as requested when touching the engine and showing good spark, huzzah thought I............re fitted all four after a second check and all looked spot on, HT leads back on and press fire..............3 cylinders except its 1,2 and 3 this time so the fault has jumped from 1 to 4?????     EH, how queer! ???

Do the whole process and the number 4 plug wont spark except about an inch away from the engine and you get a good arc! and as I was reminded, a good nibble if you catch yerself on it ;D ;D

Another wiggle and a prod, all four sparking so re fit, press go..........3 cylinders again but now its 2,3 and 4, so it's gone back to number 1!   I did this several times and always it would swap over for no reason.  STUMPED! ;D

Yes, the coils have had the 'Ash mod' and tested well afterwards so was happy with how they ended up afer the refurb which was done as the OE leads were so battered they just hung limp when you held them up and were snapped in various places. Anyway, questions, questions...

I realise there's nothing mechanical in the coils and nothing moves so I can't even picture this fault and how it might be happening or the reason why it might be swapping from primary to secondary coils, if I'm gettig that reasonably right?
 Has anybody had a similar fault or heard of anything that might be somewhere near a similar event that might explain it or promote it. As its intermittant  fault it's hard to pin down and especially when I have no 'concievable' way of thinking why or how it might be happening.

Me annd Ken had a chin wag the other night about it and he's stumped also but one potential thing to look at maybe is the engine cases behind the rotor plate of the points, possibly  There might be some cerekote on the end of the cases that might be breaking contact with the points plate and the motor? Probably not but I'll do the easy checks first before firing the parts canon or removing stuff,
Condensers were also mentioned and a test wil be done on those  whilst I'm at it but for the most part we were clutching at straws and a bit lost.


I'll have to get another coil set I think but I'll swap the blue and yellow wires to the current set and see if I can replicate the events but even if I can I think the safest bet is to buy a new set.  I would still like to understand how it can jump from one side to the other at will, all sparking outside the motor  but not when the plugs are back in the motor. Just a, well,  really odd one.  :o

Sorry about the epic but it took some describing...............

K2-K6:
Certainly a bit peculiar  :)

Thinking the same as you, swap the condensers over between the two sides to see what that does. Moves over or nothing happens?

The resistance changes on one lead when you move the plug away, but it's still linked through that same coil. When the first plug sparks it "rings" back through the coil and points curcuit as a reaction, this can get the condenser to effectively re-fire the coil and may give that symptom or similar.

As you plan though, to eliminate the coil would be ideal by substitute. 

You could swap the advance mech cam 180 degree and switch the blue / yellow wires to run the opposite coils onto the "wrong" points and see where the problem goes to.

McCabe-Thiele (Ted):
In my first two weeks of ownership my 500 was all over the place with a cylinder not firing mainly number 1.
So I could have 10 mile ride before strip down I bought a cheap pair of Hedler coils for £17 - she fired up instantly & ran on all four cylinders.
The coil leads were cracked just near where they emerged from the coils - have kept the old coils for if I ever get round to Ashs coil fix in the future.

Laverdaroo:

--- Quote from: K2-K6 on May 22, 2023, 09:31:26 PM ---Certainly a bit peculiar  :)

Thinking the same as you, swap the condensers over between the two sides to see what that does. Moves over or nothing happens?

The resistance changes on one lead when you move the plug away, but it's still linked through that same coil. When the first plug sparks it "rings" back through the coil and points curcuit as a reaction, this can get the condenser to effectively re-fire the coil and may give that symptom or similar.

As you plan though, to eliminate the coil would be ideal by substitute. 

You could swap the advance mech cam 180 degree and switch the blue / yellow wires to run the opposite coils onto the "wrong" points and see where the problem goes to.

--- End quote ---

I think thats the first point of call after cleaning the end of the cases, do the condensers etc. When I get back to it tmrw evening I'll see what occurs and try to report back with better terminology as I'm sure, "How queer" isnt really an engineering term ;D
--- Quote from: McCabe-Thiele (Ted) on May 22, 2023, 10:07:57 PM ---In my first two weeks of ownership my 500 was all over the place with a cylinder not firing mainly number 1.
So I could have 10 mile ride before strip down I bought a cheap pair of Hedler coils for £17 - she fired up instantly & ran on all four cylinders.
The coil leads were cracked just near where they emerged from the coils - have kept the old coils for if I ever get round to Ashs coil fix in the future.

--- End quote ---

Laverdaroo:

--- Quote from: McCabe-Thiele (Ted) on May 22, 2023, 10:07:57 PM ---In my first two weeks of ownership my 500 was all over the place with a cylinder not firing mainly number 1.
So I could have 10 mile ride before strip down I bought a cheap pair of Hedler coils for £17 - she fired up instantly & ran on all four cylinders.
The coil leads were cracked just near where they emerged from the coils - have kept the old coils for if I ever get round to Ashs coil fix in the future.

--- End quote ---

New HT leads on teh fix so ruled that out Ted.

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