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Allan G, Beach, GrandPaul, Nick H, NickL, triton thrasher
Total Likes: 22
Original Post (Thread Starter)
#853298 07/08/2021 5:00 PM
by Nick H
Nick H
Some years ago when I first got interested in bikes again I struggled for a loooong time with a no start custom Triumph T120.
I was getting spark from the Boyer MKIII so I thought it was fine. I did suspect it though so I bought a new MKIV and still had trouble.
Eventually I sent them both to John Healy who confirmed the MKIII was not advancing correctly but the new MKIV was fine.
In the interim I had switched to points and stayed with them on the custom. The bike ran great.

Now I'm putting together another custom T120 and thought give the new MKIV a try.
I get sparks when I touch the leads together but not when I kick over the bike.
This would indicate a problem with the timing plate or magnetic rotor I would think. They have never been used and it doesn't look
like a problem with the leads to the little coils. Impedence there is 141 ohms, close enough to what should be 137 ohms I would think.
The rotor magnets can support their weight.
The battery is new and seems good. The 6 ohm Lucas coils are old but seem good also.

Any ideas before I shelf this again for points and start bad mouthing Boyer?
Liked Replies
#853343 Jul 9th a 04:34 AM
by DavidP
I forget whether it was Boyer or Pazon, or both, but some kits were supplied with a bolt which is a bit too long to properly fix the rotor into the taper on the cam shaft. You might try using a small lock washer under the head of this bolt.
You also need to be sure that the rotor magnets are not contacting the poles of the stator plate.
2 members like this
#853395 Jul 9th a 08:04 PM
by Allan G
Allan G
It’s also not a good idea to run alternator and ignition wires close/alongside or across each other.
2 members like this
#853397 Jul 9th a 08:34 PM
by John Healy
John Healy
"but maybe not the best idea anyway for cooling." Unfortunately Nick, it is not if, but when!

Diodes in both the Boyer box and the regulator/regulator ability to work is a function of temperature.

When they are working they generate heat. If the heat is not removed they can/will fail.

When they fail, voltage from the regulator can spike putting further stress on the diodes in the Boyer box. This leads to a total failure of the system.

Add to this the higher ambient air temperatures we have been experiencing makes this worse.
1 member likes this
#853416 Jul 10th a 04:03 AM
by DavidP
Originally Posted by Allan G
It’s also not a good idea to run alternator and ignition wires close/alongside or across each other.
Even more important on triples, which have the alternator on the same side of the engine as the points.

John, maybe Boyer, et al could learn from Lucas, who mounted the Rita on a bracket which could be located in good air flow? Tough to find a good mounting place when all they give you is industrial strength Velcro and the amplifier box is plastic.
1 member likes this
#853712 Jul 14th a 07:54 PM
by Allan G
Allan G
Sorry if you have mentioned this. Have you checked the magnetism of each of the magnets on the rotor? A weak magnet won’t work. It should be able to support its own weight or the weight of a small spanner.
1 member likes this
#853920 Jul 17th a 06:56 AM
by quinten
Remember, my wiring is negative ground so I believe I can measure volts at the coil.
In any event it can be done the way shown in a Vintage Bike article.

you shouldn't be able to read voltage at the coils
wirh negitive ground ( if the boyer is correctly wired and ready to fire )
the test requires a simple wiring change .

you can voltage-drop load-test using coils as the load
if black wire between B-box and coil is pulled from box and grounded
the coils are the load ... and this will also test the conductivity of the ignition wiring .
... all its various crimps and connections
1 member likes this
#853950 Jul 17th a 05:43 PM
by Stuart
Hi Trevor,
Originally Posted by BSA_WM20
Originally Posted by Stuart
Proper DC regulation, high-output 3-phase alternator doesn't damage a 7 Ah burglar alarm battery ...
And when do most BSA's end up with proper DC regulation ?
The sentence you've quoted was my agreement with part of one of Nick H The O.P.'s posts:-
Originally Posted by Nick H
My battery is a 4 AH. Not great but i wouldn't think my single phase charging system would damage it.
As for your rhetorical question, educated guess says you're dissatisfied with the regulation by the standard Zeners fitted to BSA's with 12V electrics? If so, fit a modern reg./rec.?


1 member likes this
#853978 Jul 17th a 11:52 PM
by quinten
not sure whats hooked up and not hooked up
when you get your voltage readings and where youre putting the meter probes .

With the jumper in place for neg. ground ... jumper between black wire and coil ... jumper to gound
... ignition on ...the voltage reading should be zero at the jumper .
you can trace the voltage drop around the circuit as it meets resistance .
the voltage before the first coil may be lower than voltage across battery terminals ... indicating wire and switch loss .
and the voltage will be half remaining voltage between the coils
and zero voltage after the second coil .

and battery circuit voltage will be somewhat lower than resting voltage , indicating the coil load ... but still above 10volts
... 10 volts being the safe low voltage at which the B-box will still latch and time correctly without Jitter .

the battery voltage under coil load is also testing the battery strength .
a bigger drop indicates of a weaker battery ... and or a smaller battery with less reserve .
dont know if your negitive wiring is correct ?
look at fig 3 and fig 4 below
the wiring for the boyer is the same for pos. and neg . ground ... only the switch location moves ( the fuse moves to ,
if you follow the convention of fusing the switch slde )
[Linked Image from]
1 member likes this
#854036 Jul 18th a 07:16 PM
by Stuart
Hi Nick,
Originally Posted by Nick H
Quinten and Stuart are telling me I can't measure voltage at the coil in my negative "ground" (I've learned to always put it in quotes) installation
or I've done something wrong.
Uh-uh; to clarify:-
Originally Posted by Stuart
you cannot measure Volts in any circuit containing a B-B e.i. or one of the clones, because ...
Originally Posted by Nick H
I made a jumper from the black wire coil to "ground"
. on your bike, "negative ground" means metal bits of the bike are connected to battery -ve;

. "black wire coil" means the (B-B) Transistor Box Black wire is connected to coil -ve;

. "I made a jumper from the black wire coil to "ground"" means you connected battery -ve to coil -ve; i.e. you bypassed the Transistor Box, it was not in the circuit that you were measuring Volts, your Volts readings were (should've been) accurate.

Originally Posted by Nick H
measured at the red wire coil. It measured battery voltage less any loss from the switch, etc.
However, afaict this is incorrect ...

. First you measure between battery -ve and battery +ve, to get a reference = none of the bike's electrical components involved;

. then you can measure between:-

.. coil -ve ("black wire coil") and battery +ve;

.. battery -ve and coil +ve ("red wire coil");

.. note the opposition of the two terminals in each phrase, because the coil/s is/are the resistance in the ignition circuit;

.. if there isn't any additional resistance in any other component in the ignition circuit (e.g. across fuse, ignition switch, kill switch, etc), the Volts readings above between each coil terminal and battery terminal should be the same as the first reading just between the battery terminals;

. so there should not be "any loss from the switch, etc."; if there is, the component/s where this "loss" occurs is/are faulty.

Originally Posted by Nick H
Even without the jumper I still measure battery voltage at the coil.
This measurement only thumbsup while the B-B Transistor Box is conducting; when it switches off, any Volts readings anywhere in the ignition circuit are thumbsdown same as they would be if the ignition or kill switches were off, any fuse was out or blown, etc.

Originally Posted by quinten
you shouldn't be able to read voltage at the coils wirh negitive ground
confused 'Fraid I have no idea what this means ...

As I posted earlier, and you can see in the B-B wiring diagrams, any e.i. is connected exactly the same, totally and utterly irrelevant of "ground". In the case of B-B or Pazon/Wassell clones, the Box White wire is connected to battery -ve, the box Red wire is connected to battery +ve, the Box Black wire is connected to coil -ve (only one coil -ve in the case of multiple coils), (one) coil +ve is connected to battery +ve. That's the ignition circuit. The position of any switches within the circuit might be different but they are (should be) simply connections within the circuit.

Because any e.i. is connected exactly the same, irrelevant of "ground", if the e.i. Box is powered down, the ignition circuit is not complete, any Volts 'readings' aren't meaningful. Bugger-all to do with "ground", "negative" or 'positive'.


1 member likes this
#854077 Jul 19th a 08:33 AM
by quinten
Originally Posted by reverb
Hi Quinten; why is safe to use a bare ground wire? Is that is just grounded? I am confused by the idea that if a battery has 2 poles the current would go from one passing for the wiring and finishing on the other pole? Or is not that way?
Decades ago I saw that in houses but as I am not interested in Electricity theory etc I forgot about it.

a low voltage DC earth side doesn't need insulation to function correctly .
the insulation on the gound side only add a layer of protection against accidents .
you " could " wire the ground side harness in all bare copper wire .
(theres probably a trailer Queen Chopper somewhere build this way )

many parts of a motorcycle ground-side are not insulated .
some are conductive paths , some are just bonded to ground to convey a known polarity .
the engine is part of the ground path , its not -insulated .
the handlebars are un insulated and even if rubber mounted
are likely conductive through the clutch cable .
the frame is bonded to ground . paint insulates the frame
but any of the nuts and bolts attached to the frame may be un-insulated earth points .

adding a few inches of bare copper bond between engine and earth harness
adds little to the mass of already non -insulated engine .

do live wires fall off and contact engines , handlebars or aluminum fenders ?
yes , I suppose they do sometimes , but most of the time the lack of insulation isn't an issue .

nowdays , and for some time ,
Conductive metal bits are all bonded to the ground side with copper bond straps
even if the bits are not intended to be the pimary conductive ground path .
and this includes all bare metal conductive bits .

back when cars had chrome bumpers you could jump a dead battery in one car
by kissing 2 car bumpers together to form a negative connection , Through both frames
and then add only one jumper wire from battery+ to battery +.
1 member likes this
#854088 Jul 19th a 02:17 PM
by Allan G
Allan G
you might want to look at what is chafing your chain, those polished plates don't look too promising eek

and whilst your down there, fit a cover plate between the chain and the battery. It might be in a box, but theres a lot of grease and sh** that will by flying about down there.
1 member likes this
#854468 Jul 23rd a 02:39 PM
by Nick H
Nick H
Thanks for the very helpful comments!

Allan, we went through my reg/rec wiring location once before on my BSA. Thank you again I'll try to get it through my thick skull.

I think dual coils are fairly commonly used with points. One condenser, two? Here's the one that was working on this engine when I bought it (!):
[Linked Image from]
It's only 4 inches tall and has no writing on it so I don't know what it is.

I'm thinking now that I may have had a problem with my plug wires with the Lucas coils or the coils themselves. Both quite old.
The spark that I was getting did not look very strong.
I'll stop blaming the Boyer.

Stuart thank you for the education on fusing. I'll make the adjustment for sure.

Originally Posted by reverb
...besides the possible electrical problem; chromed carburetors is a good way to cry a lot with the many hassles incorporated.
I've heard it said that chroming an Amal does it no good but I do know of one person with chromed Concentrics that work fine.
I didn't have these Monoblocs chromed, I got them this way but it is a flashy effect for this bike.
I suppose I should post a photo of the bike.
1 member likes this
#854076 Jul 19th a 08:33 AM
by Allan G
Allan G
Having a bare ground wire is as safe as having bare sections of frame or engine.
1 member likes this
#854573 Jul 24th a 01:22 PM
by triton thrasher
triton thrasher
Originally Posted by quinten
Possibly because
the fuse at the battery isnt the only ground point ... so doesn't break all connections
whats not shown on the diagram is
the old finned rectifier had its own ground .

Originally Posted by john healy
... and suggest that the fuse should have been put on the ground side of the battery. Well, in 1966 they did just that, but they discovered: if the fuse failed while the bike was running the bike would keep running and damage the rectifier. The next year they change the harness with the fuse on the feed side of the battery

I don’t understand that. I probably need Stuart to explain it!

Yes, a bike can keep running on the charging system with the ignition switch on and the battery isolated, such as by a blown fuse. I don’t see what difference it can make whereabout the battery circuit is broken: near the live terminal or near the return terminal.

I must take a look at the later Triumph diagrams.
1 member likes this
#854589 Jul 24th a 06:14 PM
by Allan G
Allan G
Nick, if the points are running good, I’d stick with them until a time that you find that the persistent servicing and retiming of them either becomes a chore or takes up too much time when you have other commitments. For me it was the latter and I went onto the electronic ignition.

Just be sure you have the 12° degree advance AAU and not the 11°. The 11° is the 4 ca type and the cause for many an engine failure.
1 member likes this
#854615 Jul 25th a 04:25 AM
by DavidP
Every 'modern' bike has a multi-circuit fuse box, doesn't leave one guessing which element caused the one fuse to blow.
As a minimum these days I use a 15A on the common lead and a 5A in the circuit to the coils on the EI. Since the common lead goes directly from the battery to the single point on the frame, from which all other common wires originate, I don't see how the frame is still energized if the fuse blows.
1 member likes this
#854987 Jul 30th a 09:34 PM
by triton thrasher
triton thrasher
Originally Posted by Nick H
The motorcycle in question
[Linked Image from]

That’s a tragedy.
1 member likes this
#854986 Jul 30th a 09:14 PM
by Andy Higham
Andy Higham
Take it away, it makes me feel sick
1 member likes this
#855049 Jul 31st a 02:55 PM
by Allan G
Allan G
Each to their own. It’s not my cup of tea but it’s not my money either, so it’s none of my business.

I think if you’ve asked for help over a certain topic then that’s what should be assisted on.

You might be interested in the specials board on this site, it seems to have gone quiet of late but was bristling with info on specials/choppers/bobbers etc at one time.
1 member likes this
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