Twin Plug Coils

Hi Gurus, My 1200 Sport (2V dunger, twin plugs) has been erratic of late especially at idle or low throttle positions. I suspect any of these:
- Coils
- Plugs
- Leads
- ECU
- TPS
- Other

Experimentation with throttle +ve did not reveal anything, nor did removing and cleaning TPS sensor. Replacing plugs did not change anything either.

Ordered a set of 4 x 7mm plug leads to make my own set up, these arrived yesterday. Today I removed tank, coils and leads.

Weird, the coil HT outputs have 7.5 kOhms between them, but neither side is connected to ground, nor to the primary - the whole coil assembly is isolated from frame/ground anyway, by a set of grommets. The input is around 0.9 Ohm and is also isolated from ground (-ve terminal on battery is the reference point). One side of the coil primary is connected to +12V through a relay, and the other side is switched via the ECU - nothing strange here.

What I can gather is that the plugs/coil combination fire using the grounding of the head to complete the HT circuit, and therefore the spark. Am I daft thinking this?

Of the four leads that came off the bike, 3 are 0.2 Ohms, and one hovers around 2 Ohms - so obviously time to change them, hence the purchase. Plug caps are all within 5 kOhms, as they should be.

Any thoughts from the greater knowledge pool? Head scratching has done nothing here for me...

Incidentally the coils are made by Champion, but nothing found in their catalogue - probably a special jobbie... Late news, the Champion part number is BAE800B/245 and is fitted to lots of Euro vehicles (Fiat et al) as well as lots of bikes out of Italy

Might this be the problem?

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Unlikely.

It's VERY hot at the moment. I have a Stelvio with a similar issue in at the moment. All earths and battery positive are fine and the problem manifests as the bike gets hot.

My next guess is a scabby relay. The owner and bike have just returned from Manila. I'll do the contacts tomorrow morning but I'm thinking a relay or, worst case, an ignition switch.

Oz1200Guzzi wrote:

Weird, the coil HT outputs have 7.5 kOhms between them, but neither side is connected to ground, nor to the primary - the whole coil assembly is isolated from frame/ground anyway, by a set of grommets.

Any thoughts from the greater knowledge pool? Head scratching has done nothing here for me...

This is not unusual, many bikes share a coil between cylinders.  Honda 350 twin and 750 fours are an example.

The system works because the cylinder not under compression fires it's spark first.  This creates a back EMF which then gains enough potential to fire the cylinder under compression.  The coils are not the same as ones with one side grounded, the turns ratio are typically a lot less.

I learnt most of this when using strobes to time the ignition back in the early 70's.  Never forgot it.

This is not a wasted spark effort Dave. The same coils on Calis, Brevas, Norge et al and the fire together on the same cylinder through two plugs (inner and outer). I have had this problem for around 2 years, but it is now getting worse, so time to dig in.

Incidentally my plug leads have an extra, high temperature, plastic tubing around them - except for the one playing up. I have it somewhere, I can't remember why I took it off in the first place, as it was around 6 years ago. My fault totally. Caveat Emptor!

Not quite the same, Tony, as both plugs fire on the same compression stroke. I don't know, but I'm guessing that for the CARC bikes the turns ratio would be similar to that for a single coil.

But it's got me thinking (dangerous, I know!). Which plug fires first? Is it always the same one? Does it really matter?

Dave they fire together - only one trigger circuit from the ECU. I have replaced both sets of leads and the bike fires up and idles evenly - which it didn't before.

Stinking hot here today so it might wait until the next few days to test it - couldn't be arsed gettin all my gear on, sweat is just running out of me at the moment, as I cut the back grass, fixed my bike and bathed the two dogs.

I feel like it's beer o'clock but it's not even midday yet (not that that will stop me, but we are supposed to be going out for lunch today).

It was 35° (That's 95° F) when I dragged my arse out of bed at 7. It's now 43° (109° F).

Feck this heat. No riding for moi.


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Mark, you simply can't ride fast enough to get the cooling effect. Beer it might have to be.

Hmm. You know that thing I mentioned? It's kind of back. Mostly.

Oh

shit I started with the beer at about 10:40 today.... day two of mowing. thought I'd going to drop yesterday behind the mower thank god there was icy cold beer in th fridge!!

back to your spark issues. yes, it true, as age approaches, the spark diminishes...
oh wait, on Black Betty.... is pic 3 the lead with out the extra tubing??

Yup, and a dodgy spot where short cuts were taken by said spark. You can see the burn map as it comes across the rocker cover

Well, while the leads did need changing, the problem is still there, when the old girl gets a bit of temperature in her. Maybe the coils, maybe the TPS are the next two questions that would need answering. Anyone know of an alternate supply of the TPS?

PF1C common equivalent.

Get one here:  CLICKY

On the Stelvio I've just done it was the phase sensor. I still have one in stock if you want to try it Tony?

Yes please Pete, I'll give you a ring tomorrow - things are a bit hectic here today.

Mark, thanks for that link.

No worries Tony. I'll stick a couple of depth shims in with it.

The way to check the depth is correct without taking the timing chest cover off is to take the shims off the old one and then just compare it to the new one by them by putting them face to face next to each other. If the 'Tube' of the sensor is the same length they ell just touch each other's mounting plates. Normally they are but if the new one is significantly longer? Add shim. If it's shorter? Remove shim.

Just PM me your address and I'll pop them in the mail. I've done three phase sensors in the last mont. I think it's the heat cooking them! 43*C days are a bastard on electrical stuff.

Pete, again, many thanks. Thinking about it, I never even considered the phase sensor - though it IS critical for all things to work properly - shame it's such a PITA to get to.

Phase sensor is an inductive type and reaching back into the dark recesses of one's mind, it should be painfully obvious that magnetic things like this (don't shoot me down because it is the changing flux of a coil due to the proximity, or not, of an iron core - this is a special kind of magnetism called electromagnetism) can easily become less gooderer with the application of heat, and oil, and age, and lack of maintenance. It really is in a hostile spot, and some years back the oil mist collector split itself (presumably laughing) as I was in transit to the Ruptured Budgie. Oil was everywhere.

Anyway, Pete is assisting us mere mortals again with his deep knowledge of things to do with life and Guzzis.

Ahem. I seem to remember mentioning the phase sensor in a PM dated Fri Dec 06, 2019 12:40 pm.

Yes you did Mark, and I with a poor old blokes memory, simply forgot. Sometimes I need hitting with the reminder stick more than once.

Sorry.

Wel, the numbers are in (well the phase sensor is anyway) and when hot (1+ hours riding) the same symptoms exhibit. Next on the list is the TPS and then a set of coils, as it's heat related and these things are the originals.

Eventually, by elimination, I'll have rebuilt a bit of the running system.

Pete let me know $ for the sensor as I am not taking it out, again. Call me lazy, but I'd rather have a known 2nd hand spare on hand, with a good 'un in the bike.

Send it back Tony. I need it for another bike.

OK will do Pete, maybe I can get it done tonight or tomorrow night.

New TPS installed last night. No change to the miss. Next - a pair of new coils. Arse!