Misc: Ignition BTH Magneto sparks erratically...

macvette

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Out of curioustity, I checked the earthing of the bth on my twin with my multi meter. It's standard installation with the O ring. There was close to zero resistance between the mag body and an adjacent point on the crankcase and likewise between the mag case and the earth point on the frame. Having said that, I did have a misfire at higher revs which turned out to be interference in the kill button wire.
 
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BigEd

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Out of curioustity, I checked the earthing of the bth on my twin with my multi meter. It's standard installation with the O ring. There was close to zero resistance between the mag body and an adjacent point on the crankcase and likewise between the mag case and the earth point on the frame. Having said that, I did have a misfire at higher revs which turned out to be interference in the kill button wire.
There doesn't seem to any obvious answer to why the kill wire interference causes problems on some bikes but not others. I believe that the present manufacturer supplies the new BT-H magnetos with a screened kill wire. Maybe someone who has purchased one recently might be able to confirm this.
 
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macvette

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Mine does have the screened kill wire but because of other issues it took a while to identify the interference problem. Once I found it, I could reproduce the symptoms at will by changing the routing of the kill wire.
It seems to occur on a few installations but I don't know if it's the bike or the Bht, probably both. If earthing doesn't work, I would check the kill wire routing.
Mac
 

greg brillus

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As a point of interest..........When I spoke to the chap from BTH not so long ago I asked if he sells many that are twin spark types, and he said that about 50% or so where. Then I asked if he knew if the advance curve for the twin spark set ups were different to the single plug type...........He had no idea what I was talking about. I actually found this almost too hard to believe, as I explained to him that a twin plug ignition generally runs much less advance than a single plug type. So this would indicate to me that if a twin plug set up was set at say 28 degrees full advance for a twin engine, then the retarded position would be way after TDC making starting difficult and causing the engine to run very hot at low speed. The makers of these and other electronic ignitions need to change this to get proper engine performance and reliability, a bit like when I tried to advise Burlen's how to improve the 289 carb's.............None of them listen.
 

timetraveller

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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.
 

greg brillus

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I actually have one here that is on a freshly rebuilt 600 Comet engine and we have decided to run it as a single fire only. The chap from BTH said that basically on the twin fire version that two output coils are driven from the one output within the unit itself. I asked if anyone had any complaints or suffered any issues from the ones sold, but he said "Not really" But I know of several who have engines that have had mechanical failures (piston) or are very difficult to start. As far as I can tell the only ignition unit that seems to be made with the correct advance to suit twin plug ignitions is the electronic ones made by Grosset in France. I recently installed one on a modern Egli running a 1000 cc brand new engine with the squish band twin plug heads (terry's ones) and it is set up so full advance is set at 28 degrees (recommended) and the retarded position is at 4 to 5 degrees BTDC. The owner is extremely happy and says it starts, runs and ticks over far better than it ever has before. From what I can see, the only way to get a twin spark BTH to have a better advance curve would be to install one that has "Fixed" ignition and run a genuine ADT with the travel reduced accordingly. Like I said, the chap from BTH seemed completely lost when I asked about different advance curves, as though they have always been made that way, so why bother changing............what can you do.........o_O
 

evcomet

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I actually have one here that is on a freshly rebuilt 600 Comet engine and we have decided to run it as a single fire only. The chap from BTH said that basically on the twin fire version that two output coils are driven from the one output within the unit itself. I asked if anyone had any complaints or suffered any issues from the ones sold, but he said "Not really" But I know of several who have engines that have had mechanical failures (piston) or are very difficult to start. As far as I can tell the only ignition unit that seems to be made with the correct advance to suit twin plug ignitions is the electronic ones made by Grosset in France. I recently installed one on a modern Egli running a 1000 cc brand new engine with the squish band twin plug heads (terry's ones) and it is set up so full advance is set at 28 degrees (recommended) and the retarded position is at 4 to 5 degrees BTDC. The owner is extremely happy and says it starts, runs and ticks over far better than it ever has before. From what I can see, the only way to get a twin spark BTH to have a better advance curve would be to install one that has "Fixed" ignition and run a genuine ADT with the travel reduced accordingly. Like I said, the chap from BTH seemed completely lost when I asked about different advance curves, as though they have always been made that way, so why bother changing............what can you do.........o_O

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
 

vibrac

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As I said before I can see little advantage in running twin plugs on a road bike and when on a racer and I bring the timing up (too little effect I might add) I dont think my Foxley starter minds a bit of difficulty in starting funnily enough I havent had a kickstart on the racing comet since 1965
 

davidd

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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

I am pretty sure the answer is none. Unless you are using a dyno to set the timing it will not matter. Set it on your favorite number and ride.

We have talked about this before on the forum and there is, so far, nothing to be done about it. BT-H and Pazon are using industry standard chips that are not easily programmable for advance. It is set in the chip. It can be turned off and there can be some small preliminary adjustment, but I don't think it is programmable in the ordinary sense of the word. There are fully programmable ignitions like the MSD 4217 that can be used, but it is a lot of work on the dyno to set them up.

If someone will take the time to strobe their engine they can get an idea of the advance and retard. I did this to my BT-H on the racer and I could not find any. I did not order it fixed, but the mark did not move at different RPMs, which was fine by me.

Twin spark ignitions on the street tend to provide better starting and are less prone to detonation. Not something I would bother to change from a single spark for, unless I had a specific problem that the twin spark would address. The fact that they can be run at lower timing numbers does not mean that they have to be run at lower timing numbers. The lower you can run the timing is evidence that your combustion process is more efficient. If you can pick up .3 BHP by running 10° more retarded, you can simply go back to your original setting and give up the .3 BHP.

I ran at 19°, but I started and raced it at 26° before I got to the dyno. The difference in timing did not change my standing in the races. The bike did run much faster by the end of the season with all my adjustments, but it was mostly the improvement to the Girdraulics that cut many seconds off to my lap times.

David
 

evcomet

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David,
I appreciate the answer you have provided. I have enough to do an am glad that I can leave the timing alone for now.

I just wanted to be comfortable that none harm is likely to come as a result of my advance setting.

Jerry
 
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