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E: Engine Power Arc Ignitions


Oldhaven

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VOC Member
Based on magneto problems with my newly rebuilt Rapide I started working with Power Arc three years ago to adapt their multi spark and programmable ignition to 50 degree Vincent twins and singles and to fit it in Bob Larmour's design for a magneto replacement housing. This is very similar to the Power Arc ignition that Old Britts sells for Nortons, less the housing. It has also been adapted to HDs, Hondas and even automobiles and tractors over the years. One of our great old time Vincent owners helped get this going financially by investing in the first ten units after my prototype was installed and worked well. Bob and I are both using the ignition successfully on our Rapides, one other is running on a Rapide on the West Coast, and two are currently being installed on a standard Comet and Rapide, and two more on big bore Shadows. I am just now packing up one without a housing that will be adapted to a Rita housing by a talented owner, and Cyborg did his own adaptation to a Norton points housing of one he got from Power Arc directly. That is documented here on the forum.

Like the JE steering stem, we are not doing this to get rich, but because it seemed like a good system with its standard advance curves and unlike some options was programmable, which is useful for special needs like dual plugs and competition.

The system with housing runs from around $600-$800 depending on coil choices. The optional programming unit adds to that if it is wanted, and if you have a housing you think will be useable and are as clever as Cyborg, that will take about $250 off the total. If interested please contact me by PM and I'll email you a user manual to peruse. I don't anticipate providing many more systems as that will mean investing in another lot of Bob's housings, and they may be more expensive than last time, so we will see. l have 6 housings left from the first lot.

Ron
 

b'knighted

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VOC Member
I have taken on board a throwaway comment from Vibrac about coil ignition causing backfires as it is switched on. The electric starter on my big Comet has eaten several sprags possibly caused by turning the ignition on.

The Lucas Rita system was superceded by Lucas Moira which turned itself off if the engine was not running and turned itself back on once the engine was rotated. This magneto-like feature would seem to make the system safer for users of electric starts.

Can the Power Arc system be programmed to operate this way or to make the first spark or two occur after top dead centre?
 

BigEd

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VOC Forum Moderator
....................... The Lucas Rita system was superceded by Lucas Moira which turned itself off if the engine was not running and turned itself back on once the engine was rotated. This magneto-like feature would seem to make the system safer for users of electric starts. ...................................
That sounds like a good system. There is no information about a price on the website. Has anyone actually fitted this MOIRA system or have actual experience of using one?
 

b'knighted

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VOC Member
I saw Moira described, discussed and reviewed about 2012 but I never saw it advertised for sale. Shortly after its supposed introduction Mistral either announced that they would no longer produce Lucas ignition systems, or maybe they went out of business. I do seem to recall that they were still offering repairs to Rita electronic units and I think that I saw a few “new old stock” Rita units on eBay in the past couple of years.

A replacement amplifier to replace the AB11, incorporating the ability to retard to after tdc or zero spark until second rotation and with a programmable or vernier adjustable max advance independent of the full retard setting may find a ready market amongst owners of Rita trigger or Lucas distrIbuters.
 

vibrac

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Surely the easier way is to pull the clutch in as you switch on otherwise it's Russian roulette within the sprag one time that piston and mixture will be just waiting and bang!
 

Oldhaven

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VOC Member
Can the Power Arc system be programmed to operate this way or to make the first spark or two occur after top dead centre?
The Vincent Power Arc ignition, (VPA), uses an optical encoder and has a slot which is set at TDC on the front cylinder plus others on the periphery which determine spark events. Even when supplied with power after the ignition is switched on the coil(s) will not fire until the TDC slot is first rotated past the reader on the kick or starter. The coils fire at this first TDC and now that the ignition knows the flywheel position the next and subsequent triple sparks occur at 10, 5,and 0 BTDC on the firing strokes unless programmed otherwise. If the engine does not start on the kick or starter the encoder wheel stops rotating and the ignition resets in microseconds to its initial state waiting for the TDC slot. This prevents loss of encoder position should the flywheels roll back against compression or due to backfire. I have gotten an occasional back fire if my old leg doesn't give the pedal a full stroke. I would guess that a starter, with its more positive rotation, might not do this if the timing is correctly set, unless some other factor like fuel causes a problem. The VPA ignition has so far not been used with a sprag starter, so I can't say how that would go, but a backfire caused by switching on is extremely unlikely, and I have never had this happen.
 
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b'knighted

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VOC Member
Surely the easier way is to pull the clutch in as you switch on otherwise it's Russian roulette within the sprag one time that piston and mixture will be just waiting and bang!
With the Comet starter made by Bob Dunn the clutch does not isolate the sprag from the crankshaft. Pulling the valve lifter may have worked but as my ignition switch was on the left, in front of the horn, it was not convenient. Mind you, neither was replacing the sprag.
 

Oldhaven

Well Known and Active Website User
VOC Member
More discussion here about various programmable ignitions

 

vibrac

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VOC Member
I have a set of Harley USA screaming eagle ignition coils they are red and a single unit with two coil outputs no idea of their electrical properties and how they could be utilised....
 

MartynG

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VOC Member
More discussion here about various programmable ignitions

Tri-Spark (an Australian company) do a fully programmable ignition suitable for Vincent Twins and Singles. It is called the FireBox - more info here https://www.trispark.com.au/

BTW I have no commercial interest. The listed prices are in Australian $$, so apply the exchange rate for a pleasant surprise
 

b'knighted

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VOC Member
The Vincent replacement Magneto looks to total about £370 but like the BTH it is timed at full advance with no detail of the range to full retard.
 

vin998

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VOC Member
VOC Forum Moderator
The Vincent replacement Magneto looks to total about £370 but like the BTH it is timed at full advance with no detail of the range to full retard.
Don't forget by the time UK customs and U.K. Post office have had their cut you can add 20% plus.
 

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