BTH magneto problems

[robert shennan]

Hi,

I have recently fitted a BTH magneto to my 1951 series C rapide. All went well and after fitting the bike started easily, however after a few rides out over short distances the bike became more and more difficult to start. Looking into the issue it looks like the forward cylinder spark is very intermittent although the rear is sparking well. Any ideas.
Robert

 

[greg brillus]

The only issue I ever had with a new BT-H mag was the Drive pinion (not an ATD anymore) slipped on the taper, because the nut was bottoming out just as the taper was pulling up to the shaft. I had to separate the two hub pieces, and install a washer to pack the nut out further, then reassemble the hub center. This fixed the problem well and good. Cheers.....Greg.

 

[davidd]

Robert,

The issue I have seen crop up the most is electrical problems due to bundling wires. If your kill wire is near you front lead you may have a problem. We often have a bias against checking our own installation!

David

 

[robert shennan]

Hi David,

I have separated the kill wire ( yes it was cable tied to the HT leads ) as part of the fault finding. My next move is to c/o the LT leads and see if it is a coil issue.

Robert

 

[davidd]

I used one extra coil in all the years I have used the BT-H and I am not sure I had to swap it out because I found a loose connector. The coils are cheap, but they have been quite reliable for me. I always have spares, though. When installing the plug caps I pushed through one of the wires and completely missed the core. I am using a double plug on a single.

David

 

[robert shennan]

thanks for this David, I will check the plug caps which came connected to th HT leads.
Robert

 

[Mark Fisher]

I used one extra coil in all the years I have used the BT-H and I am not sure I had to swap it out because I found a loose connector. The coils are cheap, but they have been quite reliable for me. I always have spares, though. When installing the plug caps I pushed through one of the wires and completely missed the core. I am using a double plug on a single.

David

I'm with you on this one David, I've done 20k miles on my shadow since I built the bike and the BTH was fitted from the get go. I've never actually touched it since. The only thing I don't like is the bit of slop in the timing peg holes. That's not to say something couldn't ever go wrong, but so farso good.
mark

 

[macvette]

Hi,
I had two issues with my bth. The first was caused by the internal sensor which triggers the spark coming loose so the first mag was replaced. The symptoms were as you describe except that the bike died on a ride and couldn't be restarted. BTH were very helpful in sorting this out.
The second issue was that when accelerating hard the bike would stutter. Plug checks after this occurred showed that the front plug was sooty. After plug changes, several timing checks and carb setting checks I rerouted the kill wire away from the plug leads. For the sake of neatness, I had bundled it with the plug leads , re routing cured the problem. The kill wire on mine is shielded so in theory it should not pick up interference. I will try to put a pic on here. Sorry can' do it from my I pad but I think I posted the pic on a thread I started on this sometime this year.
Mac

 

[macvette]

If you search for "bogging down" under member Macvette, you will find a pic of how I rerouted the kill wire inside a length of aluminium tube from B&Q to stop it blowing in the wind.
Mac