Misc: Ignition BTH Magneto sparks erratically...

Mark Fisher

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Greg,
What negative effects are there to running my dual plugged Comet with the BTH at 35°?
I just got it running and have advance set at 26°.

Jerry
Jerry you are doing it correctly, full advance at 26-29 degrees is about right for a twin plug on single or a twin, it really doesn't matter whether it's a BTH or any other set up. It isn't really bout the advance curve, although there are programmable ones out there. It is about where your max advance ends up, anything over 30 degrees on a twin plug set up is likely to cause pinking at best. In 2007 I set my TPV Egli twin to 37 degrees not realizing the effects of the twin plug heads that were on the bike, result was severe pre-ignition and a sheared starter gear. At this time I was using a kirby rowbottom system (which is basically a Boyer) which worked well for many years once I had realized my error and re-set to 27 degrees full advance. About 3 years ago on of the huge (harley type?) coils failed and I decided that I wanted to simplify the wiring and other aspects, so I decided to fit a BTH with twin plug set up. I have run one on my shadow since 2009 with absolutely zero issues (22k miles on the BTH so far) of course this is set at about 36 degrees as my shadow is single plug heads. So far since fitting the BTH on the TPV Egli again I have had no issues (again full advance is set at 27-28 degrees), bike starts easily, runs fine, idles fine and no pinging! I do like the ignition system being independent of the rest of the electrics so if do something silly like leave the lights on the bike will still start, other than that it runs the same as it did with the boyer. I hope this helps.
mark
 

greg brillus

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With David's race engine, I'm guessing the BTH was probably a fixed timing one if no change was noticed using a strobe light. The point I was making is that the ignition advance curve for either the single or twin spark plug units offered by BTH are the same, and this is simply NOT RIGHT the fact that the owners of BTH or other ignition systems offer single/twin spark ignitions with identical advance curves is wrong. If you run the same curve on a twin spark the overall range of advance is too much, as the full advance setting is lower than for a single spark, so the retarded position is too far retarded. Some have run them this way and got away with it, but once the engine has settled down and you start pushing it harder on a hot day, it will detonate and the pistons will be destroyed. Or if you do run with a lower full advance figure, the engine will be quite retarded at low engine speed.........This can cause hard starting and the engine will run hot because the late timing will allow the flame to burn way down the exhaust pipe. Unfortunately people end up finding out the hard way on something like this, but I would be mindful of it. As I said, the Grosset one seems to have fully addressed this issue.
 

Oldhaven

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PDVCTP1-advance.jpg


What about the Pazon twin fire system? seems to be set up for dual plugs, and I was considering this for my Comet project.

http://www.pazon.com/ignition-system/smart-fire-vincent-comet-twinplug
 

Martyn Goodwin

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If that is correct then it is a very worrying thing that a manufacturer of any ignition system should know about that. With Roy Robertson's Egli going from single plug to twin plug and then with squish band meant having to reduce the fully advanced point by about 20 degrees. perhaps someone can bring the manufacturer up to speed on this.
I had a similar experience to Greg when I phoned BT-H around 2 years back asking if they could supply a unit with just 30 degrees of advance. I wanted 4 BTDC for starting and 34 BDTC full advance. The chap I spoke to had no idea what I was on about!! Yet another example of the disappearance of the skilled craftsman, replaced by someone who simply assembles.
 

Martyn Goodwin

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chankly bore

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I, and a number of other Comet owners have, in the past had poor results with Pazon - strange as Pazon seem to be fine on twins.

As Greg observed, the Grosset solution looks like the way to go at present
Maybe I just got lucky, but Pazon twin-plug on the Comet on Steroids is faultless.
 

vibrac

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I have bth on my twin and comet racer a Lucas on the cooking comet and a real bth on my grey flash replica all perform perfectly am fitting a Pazon shure fire on the egli comet I am building why? Because it's there in the box I will let you know how it runs... Thanks for the worry
 
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greg brillus

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Not so much a reliability issue, that, can apply to any of them. It's more the built in advance curves on the electronic unit's I'm concerned about. The ignition requirements for a twin plug engine are generally different to a single plug. They should leave the twin plug engines to Aircraft ..........They have much further to fall if their ignition fails..............:eek:
 
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