bth mag ht interference.

[1660bob]

Hi All, since I got my Shadow running recently, been chasing a misfire.I had read in these pages that the BTH mag can suffer from interference from the plug leads spooking the mag "brain" by inducing a current in the black kill wire if it is too close to said plug leads. In order to avoid this, i routed the kill wire well away (or so i thought) round the front cyl, `twixt barell and rear of pushrod tubes, up to a secret on/off switch hidden under the rear of the tank, and on,into the wiring loom and up to the kill button on the bars. The misfire has had me scratching my head for last couple of weeks, so i disconnected the kill wire from the loom/ switch completely and Presto!- misfire gone-Hurrah!
It turns out that the loom passes within about 2 or 2.5" from the plug leads near the front head, and it seems this is close enough to cause the interference- seems the BTH really is that sensitive?
I wonder if better quality plug leads (shielded?-is that possible?) might help, or is it possible to sleeve the kill wire in some sort of (electrically) shielded sleeving?
Electrical Boffins out there please advise...........
Cheers, Bob C.

 

[Chris Launders]

The kill wire on my BTH is shielded along its entire length until just before the kill switch by the rear spring boxes with woven metal sheathing, it was on when I got the bike, but it should be easily available or just strip some TV co-ax and use that. They use shielded plug leads on aero engines but I think that's a bit much on a bike.
Chris.

 

[roy the mechanic]

I had a problem with mine. A phone call to the manufacturer sorted it out quickly and easily. I met him at stafford ,seems like one of the good guys. Roy.

 

[BigEd]

Hi All, since I got my Shadow running recently, been chasing a misfire.I had read in these pages that the BTH mag can suffer from interference from the plug leads spooking the mag "brain" by inducing a current in the black kill wire if it is too close to said plug leads. In order to avoid this, i routed the kill wire well away (or so i thought) round the front cyl, `twixt barell and rear of pushrod tubes, up to a secret on/off switch hidden under the rear of the tank, and on,into the wiring loom and up to the kill button on the bars. The misfire has had me scratching my head for last couple of weeks, so i disconnected the kill wire from the loom/ switch completely and Presto!- misfire gone-Hurrah!
It turns out that the loom passes within about 2 or 2.5" from the plug leads near the front head, and it seems this is close enough to cause the interference- seems the BTH really is that sensitive?
I wonder if better quality plug leads (shielded?-is that possible?) might help, or is it possible to sleeve the kill wire in some sort of (electrically) shielded sleeving?
Electrical Boffins out there please advise...........
Cheers, Bob C.

At the Stafford show last Saturday I spent some time with Peter on the BT-H stand. The kill wires are now screened as standard and Peter has also said that some people found that having a bit more air gap between twin coils may help if you have had problems.
Here is a little comment to confirm that a Vincent is only human and like humans they are all different. I fitted my Rapide with one of the new BT-H magnetos when I assembled the bike in 2008. The unshielded kill wire has been taped to the plug leads from day one and I have never had an ignition problem.

 

[greg brillus]

Same for me to Eddy......

 

[Howard]

My Comet has the kill wire routed under the engine to an "ignition switch" mounted on F106, and it doesn't have a problem.

H

 

[b'knighted]

My Comet has the kill wire routed under the engine to an "ignition switch" mounted on F106, and it doesn't have a problem.

H

Dave Johnson had wires routed under his engine wiped out by a sleeping policeman at the entrance to a stately home where he was attending an Annual Rally. As your Comet is solo you need to accelerate briskly on the approach to sleeping policemen to ensure that the take off keeps the crankcase high off the ground.

 

[1660bob]

Interesting to note that some (B-TH) mags have no problems in this respect, i wonder if there is some variation in "shielding" quality in different units, say if kill wire/ht leads from differing suppliers was used by B-TH, some better than others? Bob.

 

[BigEd]

Interesting to note that some (BT-H) mags have no problems in this respect, i wonder if there is some variation in "shielding" quality in different units, say if kill wire/ht leads from differing suppliers was used by B-TH, some better than others? Bob.

Only more recent units were supplied with screened kill wires. Plug leads are/were unscreened and supplied with solid copper core wire and non resistor plug caps. Some owners have had problems because they fitted their own leads and plug caps that may have had carbon plug leads and resistor plug caps.

 

[Robert Watson]

I have one on an early twin, the first issue was to relieve the crankcase so I could get it to fit. It has given me nothing but trouble.

First one was off on a 2500 mile trip and first day in the rain, it starts misfiring, assume water in the carbs, find a shelter and drain and clean the floats and main jet banjo. No joy, stop and change plugs, no joy, putter over the mountain for it seems the faster I went, the worse it got. Finally get into a small town and sunshine, so off with the mag cowl and inspect everything which appears to be just fine. On replacing the mag cowl, happen to look up the inside of the plugs wires where it see lovely little grooves cut at exactly the same spacing as the cylinder fins, bloody BT-H
Next is in the wilds of Waterton National park, heading for the going to the sun road, and out of no where the whole plot keeps cutting out, not even just a sporadic misfire, start stop start again, good for a few miles then repeat. Finally make a good judgement call and limp back to base. Use other bike for rest of time. When home start to look for problem, and this at a time when discussion of kill switch/RF interference is at a peak, so pull this wire well clear of everything, no joy. I like some other have a SPST toggle switch mounted. Seems it has rotated on its mount and the inappropriate terminal is veeerrrryyyy close to a frame bit, shift the weight just so on the seat and presto, lovely ground. Bloody BT-H

I dislike it so much I bought another one as a backup for the A twin!