Misc: Ignition Timing of electronic ignition

Robert Watson

Well Known and Active Forum User
VOC Member
Quite a few people here are using H D stuff. The ignition has a hall effect trigger that senses the gap in a rotating cup. On starting it uses the closing of the gap to fire the system and once a few hundred RPM is reached it then uses the opening of the gap, and advances or retards from there depending on engine speed. Obviously the width of the gap must be maintained when a new cup for a 50 deg twin replaces the one for a 45 deg twin. It also uses two different advance curves, triggered by a Vacuum operated electric switch. The switch is adjustable as to when it switches on what vacuum. One can also buy black boxes that are programable on a computer and one can set such things as a certain number of revolutions before it fires (for use with delicate electric starters, or to really annoy those with a kick starter!), at what rpm the nitrous sytem gets armed, and deployed, even vary from one cylinder to another in case your cases are machined at 51 degrees :)-)), and my favourite feature; when an engine accelerates hard there is a small lag as the sensor reads the rpm that has occurred, and not the one that is about to occur, and you can program an slight extra acceleration in the ignition to compensate for this!
When cruising along at 70 mph it runs quite a big advance - depending where the initial setup is made, in the order of 45-50 dgrees. When sufficient throttle is given, the vacuum switch operates and a more conservative curve takes over.
Spare parts in almost every major town in the world, and really bullet proof. I put thi setup in more than 10 years ago, and have not touched it since. I changed plugs before I went to Australia, not because they looked bad but because I couldn't remember (and didn't write in the book) the last time they were even out of the bike.

Robert
 

timetraveller

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VOC Member
A couple of thoughts here guys. Peter's advance and retard curve could probably by approximated by two straight lines. This could be replicated by using two different rate springs in a mechanical ATD and possibly altering the separation for one of the spring mounting supports. A clever fellow might be able to design a multirate spring to do the same. Bob's information looks very interesting. Any chance of photographs, diagrams or part numbers for those of us without H-D bits and pieces to play with?

Cheers chaps :)
 

Robert Watson

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VOC Member
Took a minute to figure out that Bob was me!

These are H D part numbers from 12 years ago - so may have been superseeded by others, but they should be able to track from this

Vacuum switch 26558-84
Spark coil 31614-83
Sensor assembly 32400-80A
Sensor kit 32400-83A
Ignition Module 32421-86
Rotor 32402-83 (need this to measure the gap width)
Plug, body 74521-77

I fitted all this into a Mistral (as in old Lucas Rita) housing. It all fits under the mag cowl but is a little cramped. I have two 3/16" vacuum lines (one from each carb - downstream of the slide) coming to a T and then to the V switch. I also wired in a light that tells me what curve is being used so I could back off the vaccum switch to run more on full advance.

I recall that the wiring plus was very finicky and I replaced it with a more substantial item, however I also recall that this was improved with an update.

I run BPR7ES NGK plugs on this sytem and like I said before change them ever few years. More than 10,000 miles on the current set and doubt I'll pull them out for that many more.

Robert
 

Matty

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VOC Member
Hi
I have had my Comet since 1956 and do around 3000 miles per year.
If one looks a the characteristics for the ATD, with the normal spring arrangement the unit virtually switches at about 2000 engine rpm from no auto advance to about 35 degrees !!
To make it easy to set for many years I just set my ignition with the points just breaking at TDC. with the ATD not advanced.
If I then jam the ATD fully advanced and check the advance, it is as near as I can measure to 35 degrees and the bike runs very well.
With my 8:1 compression ratio, I do not think the setting is very critical and am not trying to achieve optimum performance so my setting method is adequate and simple.
 

Albervin

Well Known and Active Forum User
VOC Member
Hi
I have had my Comet since 1956 and do around 3000 miles per year.
If one looks a the characteristics for the ATD, with the normal spring arrangement the unit virtually switches at about 2000 engine rpm from no auto advance to about 35 degrees !!
To make it easy to set for many years I just set my ignition with the points just breaking at TDC. with the ATD not advanced.
If I then jam the ATD fully advanced and check the advance, it is as near as I can measure to 35 degrees and the bike runs very well.
With my 8:1 compression ratio, I do not think the setting is very critical and am not trying to achieve optimum performance so my setting method is adequate and simple.
WOW. Talk about restarting a thread. TEN Years!!!
 
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