Learned something today, might help other twinsparkers

[jacksonracingcomau]

So my Dyna twin output coils failed, mate has just bought ignition from tri spark.com.au so thought I’d try their twin output coils, inexpensive, neat and small got them nicely twixt carbs with wires easy to reach.
But misfire low revs high load with machine gun banging for the audience
I went through system, isolated ignition with hot wire, cleaned everything even replaced one set of points and condenser but knew they were not problem. Scratched head and didn’t test till this morning, knew I hadn’t fixed anything but didn’t think there was anything about points ignition I hadn’t already seen

So miss still there, finally rang supplier and asked if I was chasing impossible even though rated 3.8 ohms maybe they don’t work with points?

Completely wrong angle, of course they don’t know it’s points sending the trigger
Difference to normal is I want plugs to both fire under load not wasted spark like 360 twin or bmw or 4 cyl
So he asked plug gap, .024” on all four new plugs
He said that might be push for coil to effectively jump .048” under compression.

So I set outers  at .010 left inners, now combined .034”
Fixed

Doesn’t matter what triggers the coils but not all twin output coils can cope with two normal gaps on single cylinder firing
Dyna ones did but they broke so I’ll keep with these for now and run .017 on all four

Hope this saves anyone wasting a day like I just did
Answer was too quick and easy and I learnt new trick

[Rick4003]

Good to know. Thanks for sharing.

-Ulrik

Sent from my SM-A520F using Tapatalk

[John A]

Another thanks from here! When I dual plugged my Bassa and was picking coils, I called Dyna and they recommended 5 ohm for reliability of the coils. I don't know the particulars of why that is but they've been trouble free for over 100K miles.

[Rick4003]

A question regarding the dual plugging. How have you limited the advance in the distributor?  and to how many degrees did you adjust it to?

-Ulrik

[jacksonracingcomau]

A question regarding the dual plugging. How have you limited the advance in the distributor?  and to how many degrees did you adjust it to?

-Ulrik

Mine as simple as it comes, I cut a piece of copper pipe, slipped over shaft so that centrifugal bob weights do not go �home� any more, ie limit their movement in closed position. Same springs so theory is curve the same at upper end. Degree wheel on shaft I have 10 degrees advance, therefore 20 at crank.
Timed at 10/30, never experimented further, pulls like schoolboy, starts instantly and will never pink even with worst outback fuel.
Mate that bought trispark comp ignition bought software to modify curve, we may play with this to see if there is better but as far as I�m concerned this is perfect for me.
Just on 50K Km (30 odd k miles) coils first and only issue

Footnote to original post, vaguely possible that Dyna coils did die because of plug gaps, can�t really be coincidence, all started after new plugs. Difference was Dyna coils just stopped sparking completely.
I may try them again one day with reduced plug gaps but for now tri spark coils are staying, if miss ever comes back I�ll reset gaps before anything else

[pete mcgee]

Thanks Martin.
You have just explained why the original coils I used after twin plugging kept breaking down.
I hadnt thought of this angle.
Cheers

[Rough Edge racing]

 If those are double lead coils with single armature they are not designed to fire two plugs on the compression stroke at the same time...You need one lead from each coil to the left cylinder and the same to the right cylinder.. Then both coils need to fire at the same time..... This is why the coil won't fire a normal "close" plug gap...
   This problem comes up with dual plugs on other bikes....

[voncrump]

If those are double lead coils with single armature they are not designed to fire two plugs on the compression stroke at the same time...You need one lead from each coil to the left cylinder and the same to the right cylinder.. Then both coils need to fire at the same time..... This is why the coil won't fire a normal "close" plug gap...
   This problem comes up with dual plugs on other bikes....

Surely that would work on a 360degree crank. Not a 270. The double lead coils are probably made for the lost spark operation on inline fours and pair up cylinders 1 and 4 then 2 and 3. I could be getting myself mixed up here. It's been a long time since I mucked around with fours. I did have an experience years ago with a misfire on a CB750K. Every part of the system was replaced with no effect. The plug gaps were then closed down and bingo, fixed.
Cheers, voncrump

[Rough Edge racing]

Surely that would work on a 360degree crank. Not a 270. The double lead coils are probably made for the lost spark operation on inline fours and pair up cylinders 1 and 4 then 2 and 3. I could be getting myself mixed up here. It's been a long time since I mucked around with fours. I did have an experience years ago with a misfire on a CB750K. Every part of the system was replaced with no effect. The plug gaps were then closed down and bingo, fixed.
Cheers, voncrump

 360 degree makes no difference, the single coil is still trying to fire two plugs on the compression stroke at the same time...There are coils designed to fire two plugs that's why I asked the OP what type coils...This comes up with vintage Triumphs and guys will screw around trying to fix a misfire or easily fouled plugs. I screwed around with a dual plugged Harley 30 years ago..I never solved one of the two plugs fouling because I didn't know what the real cause was...
 Honda ignition fires one plug on the compression stroke and one on exhaust stroke, the waste spark...If an ignition system misfires at the factory recommended gap you can be sure there something wrong, closing the gap masks the problem...But if it ran the same, ok....

[Kiwi Dave]

Honda ignition fires one plug on the compression stroke and one on exhaust stroke, the waste spark.

Strickly speaking, there is no wasted spark.  The plug on the cylinder that is not on compression fires first, because it is easier.  This creates a back emf across the secondary which is then great enough to fire the cylinder under compression.

I know this system was employed on Honda 750 four, and 350 twin.  I owned a Xenon timing strobe light back in the day, and was checking the ignition timing on many different makes.  It intrigued me that if you disable one spark plug, then the other cylinder sharing the same coil did not fire either.  The result was that the four wouldn't run on three cylinders, and the twin wouldn't run on one.

[Rough Edge racing]

 I'm no expert on this, thanks for the clarification. Form your explanation seems to back up it's not designed to fire two plugs in a charged cylinder. ..Here's a discussion on Brit Bike...The original poster is a friend who races in the same class as me. The person called "NickL" is an Australian who designed ignition systems...John Healy was a known Triumph dealer and factory race bike tuner...

      http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=577134#Post577134

[jacksonracingcomau]

360 degree makes no difference, the single coil is still trying to fire two plugs on the compression stroke at the same time...There are coils designed to fire two plugs that's why I asked the OP what type coils

360 deg triumph etc fire every other stroke unless they’ve been twingled which needs cams grinding, mob I bought coils from use these coils exactly for normal 360 twins

Didn’t see where you asked but of course answer was in my original post trispark.com.au, coils are on this site

The way Steve there explained it was pretty simple, just the output of the coil determines the size of spark and therefore plug gap. Without a dyno I can’t say for certain these coils perform same as Dyna ones absolutely but am certain closing gaps fixed miss and feels perfect.
As I said I will equalise gaps, I’m happy to have it running well again, the knowledge why was all I wanted to share.

[voncrump]

If those are double lead coils with single armature they are not designed to fire two plugs on the compression stroke at the same time...You need one lead from each coil to the left cylinder and the same to the right cylinder.. Then both coils need to fire at the same time..... This is why the coil won't fire a normal "close" plug gap...
   This problem comes up with dual plugs on other bikes....

What I took this to mean is that the coils fire at the same time, one HT lead on  each coil goes to each cylinder. This would mean each coil is only firing one plug under compression. The other plug is in the other cylinder and fires on exhaust. That seems to be very clever but would not work on a 270degree motor. Does that make sense. Over and out.
Cheers, voncrump.