Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board 6v coil on 12 v machine?

Bike sat for a month and on start has a miss on LH cylinder.
Disappears pretty much under load, reappears on idle and cruise.

New plugs, no help.
Swapped HT leads, no help.
Ordered new coils. I have no maintenance history for the machine, so figured no harm anyway, even if not the culprit.

Removed LH coil has no manufacturer mark, but does have 6V on phenolic cap.
What happens with a 6V coil in a 12V system?

Cheers.

addendum - has a Wassell Vape EI setup installed.

If you have 2 6V coils in series then that works in a 12V system, its how they are setup for boyers and other flavours of EI.

If you have a Boyer then the favourite failure giving symptoms similar to yours is the wires failing near the pickup coils on the stator inside the timing cover,

HT from each coil to each plug.
Assume they are separate?

6V coils wired in series is recommended for his Wassell Vape ignition too.

You probably meant to say “stator inside the timing cover.” The Wassell doesn’t have exactly the same weak spot there, but there are wires and they could break.

Yes. Their low tension circuit is in series.

Diagrams here: https://totalbikebits.com/wassell/orderpoint/prod_info/WW61495.pdf

You may have a blocked pilot jet in the carburettor.

Bad coils are more likely to fail under load.

Thanks, will check, but they are brand new Amals I put on about 200 miles ago.
Thought the pilot would only affect idle?

Strange.
Under General Data it says:
"For road applications two 12 volt coils in series are satisfactory..."
But the diagram shows 2 6V coils.
Sigh.

I've mailed Wassell to see what they say about the discrepancy in the description.

Nothing strange.
Two 12V coils in series may be SATISFACTORY but two 6V coils (or one 12V dual coil) will give the best results.

Boyer, Pazon etc. say the same.

http://www.boyerbransden.com/pdf/KIT00052.pdf
"4) For low compression engines, two 12 volt coils (4 Ohm Resistance) in series are satisfactory, but for racing and high compression engines two 6 volt coils (2 Ohm resistance) in series,or one 12 volt 3.5ohm or more primary winding resistance dual output coil will give the best results."


http://www.Pazon.com/files/PDF/PA2.pdf
"For low compression ratio engines (less than 9:1), two 12 volt coils connected in series can be used, but we strongly recommend running with two 6 volt coils connected in series or one 12 volt dual output coil with a primary resistance of 3 to 4.5 ohms."

+1

Sounds like your running a tad rich or there is something a miss with the advance of the engine. If the vehicle is under load (a modern car) will retard the ignition and riches the mixture to compensate for the given load but at low load will advance and lean off the mixture.

These old nails are a compromise, the ignition advances relative to RPMs and not cylinder or vacuum pressure. So either the main jets are working their way loose, pilots are too rich or the vape isn’t advancing much of at all.... or it’s timed up wrong.




Nope they function throughout, regardless of throttle position. Just have a greater effect at tickover.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

I put a Boyer on my 72 over 30 years ago. Kept the original 12 volt coils for probably another 20 years. Finally changed to two 6 volt coils and the spark changed from bright yellow to blue white.

did it run better?

As Alan said, richness on needle position or throttle cutaway size can make it blubber on light load.

If you cut the ignition while the problem is occurring, richness will be indicated by soot on the plugs.

Did it run better? Probably, I don't remember.

I have 6v coils on my 12 volt points ignition bike. I understand that this gives a better spark at the expense of drain on the system. Would 12 volt coils on an ei use less juice enabling it work better with a bad charging system? Mine aren't wired in series, however

Dave.

You may have ballast resistors in series with those coils, to reduce the current to the same as a 12V coil draws.

If not, you should have.

There are no resistors. I am assuming they are 6 volt as there are no markings apart from a figure 6. I will have to have another look. Maybe the resistors would defeat the object.

Dave

I think your looking at the coils in the wrong way. There isn't actually a 12v coil and a 6v coil they are actually 4 ohm and 2 ohm coils but as 4 ohm coils were traditionally used on 12v ignition systems and 2 ohm on 6v systems you can see where they get the term 6 and 12 volt coil from.

With that in mind, EI are supposed to work with 3-4.5 ohm coil resistance. Hence using 2x 2 ohm coils in series to add up to 4 ohms. ( You could also use a dual output coil of 3 or 4 ohms). If you use 2x 2 ohm coils in parallel you would half the resistance so would give you 1ohm.... So don't do that.

The reason for the ballast resistor is to increase the total resistance to try and acheive 4-4.5 ohms.
If you have a 3 ohm dual output coil for example you can fit a 1.5 ohm ballast resistor in series. The black box won't be as stressed as it's only receiving a total resistance of 4.5ohm, but the coil is only using 3ohms and will generate a stronger spark (in theory) than a 4 ohm coil.

A stronger spark will help to burn a richer mixture. But most likely what you'll find is that the plug will steadily soot up till the bike stalls and won't start again until you've changed the plugs.. as your quite possibly boarder line with your jetting this could take some time. Maybe a few hundred miles.



Totally agree with the first line and from my experience it's most likely throttle slide that's too rich. One slide less will sort it, leaning the needle a clip will help in some areas, but only at the point where slide transitions to needle jet. Changing the slide is a pain on a twin carb bike but inevitable.

Now that I’ve had longer to reminisce about the troubles I seen, I think you’re right.

Quote
I think your looking at the coils in the wrong way. There isn't actually a 12v coil and a 6v coil they are actually 4 ohm and 2 ohm coils but as 4 ohm coils were traditionally used on 12v ignition systems and 2 ohm on 6v systems you can see where they get the term 6 and 12 volt coil from.

With that in mind, EI are supposed to work with 3-4.5 ohm coil resistance. Hence using 2x 2 ohm coils in series to add up to 4 ohms. ( You could also use a dual output coil of 3 or 4 ohms). If you use 2x 2 ohm coils in parallel you would half the resistance so would give you 1ohm.... So don't do that.

The reason for the ballast resistor is to increase the total resistance to try and acheive 4-4.5 ohms.
If you have a 3 ohm dual output coil for example you can fit a 1.5 ohm ballast resistor in series. The black box won't be as stressed as it's only receiving a total resistance of 4.5ohm, but the coil is only using 3ohms and will generate a stronger spark (in theory) than a 4 ohm coil.

A stronger spark will help to burn a richer mixture. But most likely what you'll find is that the plug will steadily soot up till the bike stalls and won't start again until you've changed the plugs.. as your quite possibly boarder line with your jetting this could take some time. Maybe a few hundred miles.
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This is not entirely correct, please do not read this as 'gospel'. It's fine as a guide but that's all.

One time a mechanic inadvertently installed a six-volt (ok, 2 ohm) coil on my '67 Lightning with points ignition. (It was a coil from a Norton. He thought it would be the same, and wasn't aware that Norton employed ballast resistors.) That coil burned up on the first long ride (by long, I mean over ten miles).

For entertainment purposes only:
My current Trident came to me with three 4V coils installed and points. Kinda feel sorry for the PO trying to start it for me.
I'm guessing that the shop from which he bought it had plans to fit an EI but never got a round tuit.

At the shop where I used to work we had a customer bring in a Trident with instructions to revert to points ignition. It had a Boyer which he said had never run right. No surprise there, whoever installed the Boyer left the 12V coils in pace. I'm surprised that it ran at all.

The whole point is to get the coil(s) to draw 3-4 amps.

Nick your right, the last paragraph should probably say "In theory a stronger spark should help burn a richer mixture", the bit after it was from my own experience and relates to the jetting and not the EI. Actually to add to that if it is doing the above then your probably about 2 slides too rich.

The details on the coil resistance - balanst resistor etc is as best as I can explain it (or understand it)

A coil is say 12V in the same way that a lightbulb is 12V, it means that the component is designed to work as intended at that voltage, to produce the intended output.

You may choose to use a 6V bulb in a 12V system, by including a series resistor (which will be just equivalent to another 6V bulb), but what would be the point? Instead of all the power coming from a single 12V bulb, half the power is wasted as heat in the resistor.
In the above silly example, if the 6V bulb is a 24W, it is intended to carry 4A for full output, and will be properly bright in a 6V system. If you place the same bulb in a 12V system it will blow, unless a resistor is placed in series, but that resistor will be generating 24W of heat itself (completely wasted, and it takes quite a substantial resistor to cope with this sort of heat generation for long).
The same with a coil, except in some special circumstances.
One of those situations is where special provision is made for the system voltage drop during electric starter motor activation. I believe this is the case with late commandos, such that 6V coils were used with ballast resistors, but they would be directly driven by what was left of the battery voltage during electric starting, bypassing the ballast resistor. Or am I confused?