ET: Engine (Twin) Has Anyone Ever Bench Tested a B-TH Electronic Mag With Coils

[CarlHungness]

The reason I ask the question is last year, the last time I started my twin it took me an hour to do so..finally fired. I believed the B-TH coil(s) were bad. Bought new ones with new plugs, wires, etc. still would not fire. Installed my Lucas which puts out good spark on #1 just turning the shaft by hand. Can't get #2 to fire by hand, but puts out fine with a very slow speed drill attached. The Lucas sparks on the bike, checked #1 by attaching the plug to my Britax crash bar with a Ty-Wrap..kicked it and could see good spark. I turned off the lights in the shop and saw immediate spark. Thus, I want to test the B-TH that I thought was bad before I take the carbs off to see if I'm plugged up. Hopefully the B-TH will spark and that should tell me I have a fuel problem. This is the worst scenario I've had with the machine in three decades, I've timed it many times previously and always got it to start.

 

[Normski]

I’ve clamped the BTH in a vice and connected coils and plugs making sure the plugs are earthed to the body/vice then spun it up using a battery drill with a short piece of fuel hose pushed onto the taper and onto a piece of cut off bolt mounted in the drill chuck to give a flexible coupling.

 

[Peter Holmes]

The reason I ask the question is last year, the last time I started my twin it took me an hour to do so..finally fired. I believed the B-TH coil(s) were bad. Bought new ones with new plugs, wires, etc. still would not fire. Installed my Lucas which puts out good spark on #1 just turning the shaft by hand. Can't get #2 to fire by hand, but puts out fine with a very slow speed drill attached. The Lucas sparks on the bike, checked #1 by attaching the plug to my Britax crash bar with a Ty-Wrap..kicked it and could see good spark. I turned off the lights in the shop and saw immediate spark. Thus, I want to test the B-TH that I thought was bad before I take the carbs off to see if I'm plugged up. Hopefully the B-TH will spark and that should tell me I have a fuel problem. This is the worst scenario I've had with the machine in three decades, I've timed it many times previously and always got it to start.

Don't expect to see a big fat blue spark from the BT-H magneto, you won't, it is barely visible in any light conditions, but I have been running one on a twin since 2005, and apart from needing a couple of new external coils, it has never let me down, either kickstarting, or latterly electric starting.

 

[robert shennan]

I have my BT-H mag back at the manuf. right now getting repaired, the initial report showed some internal damage and a problem with the spindle.
Ross at BT-H has provided a helpful and informative service. Should be finished testing ( and cost received ) on Monday.
What led to this was my engine defying all attempts to start after a rebuild despite numerous valve and ignition timing attempts - wish me luck.
I can recommend sending it back to the makers for a check over and service.

 

[CarlHungness]

Don't expect to see a big fat blue spark from the BT-H magneto, you won't, it is barely visible in any light conditions, but I have been running one on a twin since 2005, and apart from needing a couple of new external coils, it has never let me down, either kickstarting, or latterly electric starting.

I'll test the B-TH but postage alone to the UK is very high and since my unit dates from 2003 they have no record of it. My Lucas should start the bike but so far it won't so will look at the fuel system. I can't get a pop out of either the Lucas or the B-TH. Thanks for the tip on the weak looking spark, I'll turn the lights off. If I DO get any spark it
'may tell me it is OK, and I know the Lucas is working, so problem lies elsewhere.

 

[vibrac]

Back when the BT-H was first produced I bought one for our racing Comet. They had a jig to run it up and test it. I could not see a spark so to prove if it was sparking they put a piece of paper between the spark plug points then holding it up to the light we could see the holes burnt through the paper!

 

[LoneStar]

OK, can someone with deep electrical knowledge explain why different ignitions produce either invisible sparks, or fat blue ones, over the same gap? And is one type of spark more effective at igniting the mixture than the other?

 

[CarlHungness]

Back when the BT-H was first produced I bought one for our racing Comet. They had a jig to run it up and test it. I could not see a spark so to prove if it was sparking they put a piece of paper between the spark plug points then holding it up to the light we could see the holes burnt through the paper!

My first thought when my bike wouldn't start last year was one of the B-TH coils went bad. I replaced the coils this year and failed to start the machine. I switched to my old Lucas. Still couldn't start it. Bench tested the Lucas and it sparked. I re-installed it, still won't start. After all of this I've had the timing chest off twice, exhaust pipes too, etc. Finally today I dug out the B-TH bench tested it with a hose on its nose, turned the drill ever-so-slowly and got great sparks from the B-TH!! Then I tore into the carbs, took the jet block out of #2, all looked OK. Then moved to #1 and found the very tiny hole (.0021) to be clogged. The reason I state this figure is because I had a piece of copper wire with that diameter and it seemed to fit the hole perfectly. My drill chart says .0021" is a #75 drill, not one you'll find in a normal drill index. Thus I think I found my problem and will try and start the machine on Monday as the carbs are leaking and need new gaskets. I tested the B-TH with the new coils and the spark is fabulous. I could count the revolutions the drill was turning, so it was extremely slow. Maybe the original coils offered less visible spark, but I am over the moon that I found the jet block hole clogged.

 

[Calle]

I have been using Naraku Coils for the past few years on my BT-h magnets.
I think the machine starts easier and at a lower spin.
Ignition coil Naraku Racing V.2 high output - 2-pin
Also very sympathetically priced

 

[CarlHungness]

I have been using Naraku Coils for the past few years on my BT-h magnets.
I think the machine starts easier and at a lower spin.
Ignition coil Naraku Racing V.2 high output - 2-pin
Also very sympathetically priced

Wow! I have no knowledge whatsoever of the B-TH or any other coil. The Naraku coils state, and this is copied
from a seller's website:

NARAKU Racing ignition coil with high-end secondary coiling. With this coil, the secondary voltage is almost doubled.
The ignition voltage of the original ignition coil is approx. 16,000v. With the "race high tension coil" released 33,000v! The advantage lies in the better "translation" of the original input power. High ignition voltage ensures clean ignition at extremely high speeds and cold temperatures. It’s not just tuning freaks that will get their money’s worth, even with the cold start issues, the NARAKU coil is still a top choice.
There are two versions of the coil available: the easiest way of distinguishing between the two is the cable connectors on the coil. Please check beforehand if the original coil has 1 or 2 connectors / pins.

It just does not make any sense whatsoever if the 'original' coils put out 16,000 v and the Naraku produces 33,000. Then why in the name of good sense does B-TH not supply the higher voltage coils? The B-TH folks sare
most certainly familiar with the coils that are on the market.
Wiring the coils: My B-TH has a permanent yellow tag on the coil that goes to #1 cylinder and if memory serves correctly 'the blue wire goes to the Black Spade and the green (to the other spade, forgot its color). Will I
have to know anything to install them? The yellow tag on the B-TH has me concerned of course as it must lead to the rear, so looking for advice in advance. I'll get some for sure.