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Misc: Ignition BTH Magneto sparks erratically...



bsaowner

Well Known and Active Website User
VOC Member
#21
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

Well Known and Active Website User
VOC Member
#22
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.
 

MartynG

Well Known and Active Website User
VOC Member
#24
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.
 

MartynG

Well Known and Active Website User
VOC Member
#25

chankly bore

Well Known and Active Website User
VOC Member
#26
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

Well Known and Active Website User
VOC Member
#29
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

Well Known and Active Website User
VOC Member
#30
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:
 

Rixon

Website User
VOC Member
#31
I looked at the Grosset ignition but was surprised to find that it retains the old ATD unit for advance. I would have expected a modern ignition system to have electronic advance curves.
 

Marcus Bowden

Well Known and Active Website User
VOC Member
#32
It's the KISS system "keeping it simple stupid"have one on daughters rap since 2000 and on my "B"rap 2006 extremely low consumption even twin plugging easy to time with red LED to go by. Happy customer.
bananaman
 

stu spalding

Well Known and Active Website User
VOC Member
#33
Has anyone ever checked magneto v points/coil v electronic ignition on a dyno? It would be interesting to see what, if any, difference in horsepower is involved, or is the leap to electronic simply because it's the latest thing? Cheers, Stu.
 

peter holmes

Well Known and Active Website User
VOC Member
#34
I think the whole automotive industry embraced electronic ignition because it is better, feeler gauges and cigarette paper are a bit archaic, but I still use them on some of my bikes, the BTH electronic is on the other bike and that works very well, in the past I have blamed it for various maladies, but it has normally turned out to be fuel related, with one exception when the coils packed up whilst on the Isle of Man
 
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Rixon

Website User
VOC Member
#35
I doubt there's a lot wrong with a well set up points system on a low revving engine. On the other hand I would doubt that any two ATD's would give the same results if compared on a test rig.

My only experience is on cars where I have had rebuilt, and new, distributors tested on a rig. Since then I've used an electronic distributor !
 

timetraveller

Well Known and Active Website User
VOC Member
#36
Magneto man would provide a better answer than me but here is my experience. Every magneto I have ever used would produce a spark, perhaps 1/4" long at the most. When I first bought the ex-Cecil Mills production class racer it had a 6 volt coil ignition system. Cecil had told me years before that he had had a special coil built but it looked like a standard coil from the outside. On one occasion while checking something I had the output from the coil to the distributor disconnected and while turning the engine over a spark came out of the coil and went to earth about 2.5" - 3" away on the crank case. It would do this repeatedly if I kept turning the engine over. I can well believe that the magneto would give a better spark at higher rotational speeds and the coil, at any normal engine revs, never seemed to have a weaker spark. The method for checking this is a simple adjustable gap that was bought many years ago as a cheap tuning aid. Roughly at the same time as I bought a colour tune glass spark plug. I have never tested a new BTH magneto. Whether the length of a spark is sufficient information to characterise the power of a spark is open to discussion.
 

greg brillus

Well Known and Active Website User
VOC Member
#37
For racing it depends a bit on what fuel you are running. Electronic set ups seem ok for racing, but because of the complexity compared to a magneto, they seem to easily suffer issues that can be difficult to trace. A magneto is better in my opinion for alcohol fuels as a magneto has less voltage but more current, and this is a big plus for igniting cold fuels...........Hence this is why top fuel dragsters use very powerful magnetos for their ignition. They put out 44 amps plus............
 

vibrac

Well Known and Active Website User
VOC Member
#38
You would be lucky to see a BTH spark I know when mine was on the test rig I could not see the spark but I could not miss the holes it punched/burnt through the fag paper when stuck between the plug gap
 


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