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Misc: Ignition BTH Magneto sparks erratically...



cybershoot

Website User
Non-VOC Member
#1
I have installed the electronic BTH magneto, the one that sparks with the two little coils and the electronic advance/retard mechanism. I'm super happy with this instrument in deed. My machine is a HRD Rapide Series B '49.
Testing the mag in the vice it sparks like hell at lowest revs but once installed at the flange were it is supposed to be fixed it sparks weak and erratically. It even refuses to spark at all. Earthing the mag off the machine it sparks again as it should. Does anybody knows how this might be possible? The Mag is actually earthed together with the crankcase ???
 

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Steve G

Well Known and Active Website User
VOC Member
#3
Had this exact condition on the Cannonball. Mag would throw a great spark when off the bike but erratic when on the bike. I sanded the mag flange and the case where it mates-up. Bolted the two clean, bare metal surfaces together and the mag performed perfectly from then on.
 

cybershoot

Website User
Non-VOC Member
#4
Had this exact condition on the Cannonball. Mag would throw a great spark when off the bike but erratic when on the bike. I sanded the mag flange and the case where it mates-up. Bolted the two clean, bare metal surfaces together and the mag performed perfectly from then on.
Thank you Steve - will try this. I'm pretty sure this will be the remedy! Did you continue to use the O ring?
 

Robert Watson

Well Known and Active Website User
VOC Member
#7
Maybe I just got lucky. I have a BT-H on a Rapide. It starts first or second kick, the kill wire is clipped with the HT leads. And it is not just a fluke, it's been like that for several thousands of miles.
 

davidd

Well Known and Active Website User
VOC Member
#8
Better still - get rid of the kill wire totally
My friend Jim Young was left high and dry when his BT-H stopped working. After getting it home he found that when he clipped off the kill wire and sealed it he left just enough to get it trapped by the mag cowl. It was just enough to ground out.

BTH Jim Youn 2015 TT 2.jpg

BTH Jim Youn 2015 TT 3.jpg

I am careful about the installation, but like Robert, I tend to do what I want, as long as it works. Sometimes what we think will work does not.

David
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
#9
My friend Jim Young was left high and dry when his BT-H stopped working. After getting it home he found that when he clipped off the kill wire and sealed it he left just enough to get it trapped by the mag cowl. It was just enough to ground out.
I am careful about the installation, but like Robert, I tend to do what I want, as long as it works. Sometimes what we think will work does not.
David
Some people have found a cure for erratic running by removing the kill wire others like Robert and myself have no problems with the kill wire clipped with the HT leads. (Mine has been routed together with the HT leads since I built my Rapide, 40,000 + miles ago and counting.) The kill wire is not essential so if you think it might be causing a problem snip it off leaving a short (well insulated) piece so you can restore the kill wire if that is not the cause of a problem. If earthing might be causing a problem Davidd's photograph of his magneto shows how simple it is to put on a good earth. Most things electrical work better with a good earth.
 

greg brillus

Well Known and Active Website User
VOC Member
#10
Had a customer call in the other day with a BTH that was suffering a miss in the engine, found to be one of the terminals on one of the output coils that was loose. Once crimped up nice and firm, no miss no more............:)
 

macvette

Well Known and Active Website User
VOC Member
#11
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

Well Known and Active Website User
VOC Member
VOC Forum Moderator
#12
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

Well Known and Active Website User
VOC Member
#13
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

Well Known and Active Website User
VOC Member
#14
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

Well Known and Active Website User
VOC Member
#15
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

Well Known and Active Website User
VOC Member
#16
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

Well Known and Active Website User
VOC Member
#17
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

Well Known and Active Website User
VOC Member
#18
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

Well Known and Active Website User
VOC Member
#19
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

Well Known and Active Website User
VOC Member
#20
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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