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Discussion Starter · #1 ·
i searched around for an answer but really didnt find a solid one.
my question is:
when you use a harley dual fire coil on a triumph,do you gap the points at .020 instead of the stock .015?
im wondering because a couple people told me to gap them at .020,but want to make sure.
something to do with more ohms in the harley dual fire coil.
any truth to any of this?
thanks.
 

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when you use a harley dual fire coil on a triumph,do you gap the points at .020 instead of the stock .015?
im wondering because a couple people told me to gap them at .020,but want to make sure.
something to do with more ohms in the harley dual fire coil.
any truth to any of this?
thanks.
Nothing to do with ohms. It has to do with the fact that you're trying to get a coil made for use with single points to fire correctly with dual points. On the stock Triumph with dual points (one lobe on points cam) and 2 coils, the system operates as 2 independent ignition systems. When you use a coil with a single primary and dual secondary windings with dual points hooked together at the primary terminal, the dwell is all wrong. It won't fire unless at some point both contacts are open. Opening the gap achieves that, but it's a half ass fix. The correct way is single points on a dual lobe cam firing both plugs at once with waste spark on the exhausting cylinder.

Bob
 

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Bob's got it close.Here's some more detail to consider.
The coil resistance should be about the same as a standard Triumph/Lucas coil,about 3-4 ohm.Some coils made for electronic ignition are 1 ohm or less and will draw too much current and cause problems.

If your AAU is set up perfectly and running true (no variation in points gap around the high part of the cam lobe),you will get 160 degrees dwell angle at 0.015" points gap.If it's not running true,you should straighten it.They all get bent,when people hammer them to remove them..

With 1 coil for each points (standard set-up),the points close for 160 degrees of cam rotation and power goes to the coil.Then the coil has 200 degrees of cam rotation with no power,so it can cool off.Duty cycle = 160/360 = 44.44%
Connect 2 sets of points to one coil and the coil is energised for 320 degrees cam rotation,and only has 40 degrees cool-off time.Duty cycle =320/360 = 88.88%.

Most points/coil systems use not much more than 50 % duty cycle,so the coil won't over-heat.
Your still only getting 160 degrees dwell to produce 1 spark,but the coil now does this twice in one cam rotation.Both points are only open at once for 20 degrees,then one set closes again for 160 degrees.If the AAU is not running central,the points may not even be both open at the same time at all.

If you increase the points gap,the dwell angle and spark energy are reduced (it will only be noticable at high rpm).The coil will run cooler.At least there will be some time when both points are open at once.

A points cam that had less dwell angle would give the coil an easier life;the coil would run cooler.Triumph did use a points cam with only 86 degrees dwell,up until '67,but it wrecked engines and melted pistons through stray sparks happening when the points closed (if they bounced) at the end of the intake stroke.

A single dual-lead coil can work with 2 sets of points connected,but 2 coils with 1 points set each will work better.
 

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Discussion Starter · #7 ·
ok. thanks guys. that was some very good info (good enough to copy off and put on the fridge).
im just going to put the stock coils back on it. sounds like that is the best thing to do for the bike.
thanks again.
 

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I run a Harley coil on my Triumph with points and had some problems at first when gapped at less than .020. At higher rpm it had a miss. Increasing the gap to .020 fixed it and now complaints now. Single kick starts are the norm and no miss.
 
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