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Boyer Bransen B25
#814177 06/27/20 10:12 am
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Hi All, I've got a 1971 B25 and have fitted a Boyer Bransen electronic ignition but am having problems. Crank set up correctly at 37 degrees BTDC and magnet set in correct position, i.e. trailing edge of magnet at the 9 O'clock hole but it keeps on kicking back (almost broke my ankle). Anyone else had this problem?


1971 B25
1958 BSA M20
1960 C15
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Re: Boyer Bransen B25
Treforissa #814178 06/27/20 10:55 am
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Until you strobe it the initial static timing will be out, a consequence of the tolerances in the electrical components and distance of magnets from the trigger coils varying due to BSA tolerances. So strobe it, but a bit of retardation before you strobe it sounds in order. Running it long term over advanced is guaranteed to put a hole in the piston.

Re: Boyer Bransen B25
Treforissa #814183 06/27/20 12:16 pm
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Kicking back can also be down to a poorly set carburettor.

When you do get it started, strobed up and gone for a decent run. Adjust the idle circuit. You want the horizontal mixture screw so that it gives the fastest rpms, too rich or too lean it will drop in revs, unless you have a digital rpm readout it can be hard to tell exactly so screw it back in until the revs just start to drop.

With the slide screw (diagonal) you want that as low as you can whilst maintaining a stable tick over.

There should be virtually no gap under the slide when the throttle is closed, this way the idle circuit is solely in play when the bikes started and ticking over. If the slide is raised a little it can cause nasty kickback.

You can also try starting the bike at full throttle, you shouldn’t get a kick back from this, if you do then it’s still a timing issue.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Re: Boyer Bransen B25
Treforissa #814198 06/27/20 2:35 pm
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i believe there has been discuzsion of Boyer problems with bsa unit singles. mine would not work at all-- it ran at full advance all the time. id strobe it to set the running timing but then when tbe engine slowed it would not retard.

kicked like a bitch


now i have pointz in it and it advances and retards normally


every day you do not take a chance is a day of your life that you will never get back.
Re: Boyer Bransen B25
Treforissa #814199 06/27/20 2:38 pm
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Two things that might cause a kick back.
Low battery volts
Bad electrical connection causing low voltage to Boyer.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
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Re: Boyer Bransen B25
Treforissa #814200 06/27/20 2:59 pm
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The MK4 Boyer is fixed ref low voltage, so it now has to be really low instead of slightly low to give advanced timing.

Re: Boyer Bransen B25
kommando #814207 06/27/20 5:20 pm
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which Boyer ?
did you install this yourself ?
did the bike run on a previous ignition ? or is this a new or unknown engine build .
Standard positive ground ?

the ignition box
and the coil
each need a sound ground wire connection .
These are shown as a parallel Looped connection off the coil to the box , on the wiring diagram .
these 2 simple connection are sometimes fudged , on an otherwise sound installation .
the ground connections are as important as the power-in connection

Re: Boyer Bransen B25
quinten #814208 06/27/20 5:28 pm
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more hard start troubleshooting ( sorry this got a little bit wordy )

1. the transistor box needs a certain minimum voltage to maintain timing . ( somewhere around 10 volts )
low voltage at the white wire into the transistor box ?
(the output to the coils is normally off , so you can only check for consistent voltage at the input)
12.7 volts at the battery ... should be very close to 12.7 volts delivered to the transistor box .

"shade tree" test the battery capacity with the headlight ... will it light the headlight for 5 minutes ?
if the light dims quickly ... the battery capacity is suspect . .. with a voltmeter you can watch for voltage drop at the same time .

2. sometimes it not low voltage , but low amperage ,.. this is a power connection
some part of some wiring is compromised
( aka bad connection ... frayed wire )
the test is , to see if the same white wire , at the transistor box ... will light a 12 v incandescent filament .
a standard brake light/ tail light bulb is about the right wattage .
Jumper in the larger brake light filament ...
filament glowing brightly indicates adequate Amperage and voltage to run the ignition box and coil .

3. It's fairly easy to hook the 2 Leads from the stator to transistor box backwards
( confirm these connections , or switch them around .)

4 . 250 singles can be harder to start . There's only one spark opportunity every 720° of crank rotation .
the same ignition on a 500 twin would have twice the start opportunities ... one every 360°

the transistor box goes into standby after 2 seconds ... making it slightly harder to start the bike
because a small part of your kick is wasted in waking up the box .

tickle the carb and whatever the rest of your start drill is ... before turning on the ignition .
you have about 2 seconds to kick , and 2 seconds between kicks before the box goes into standby .
( turn the box off if you must take a break from kicking to remove your jacket and wipe your brow )
... its a silly little start procedure , turning on and off in ignition , it may not be necessary ... but can be helpful
Starting a recalcitrant single with electronic ignition .

Re: Boyer Bransen B25
Treforissa #814228 06/27/20 9:51 pm
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on my B44, the Boyer would not retard even at 13.6 volts at the box.

no ground issues.


every day you do not take a chance is a day of your life that you will never get back.
Re: Boyer Bransen B25
Treforissa #814232 06/27/20 10:43 pm
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Quote
1. the transistor box needs a certain minimum voltage to maintain timing . ( somewhere around 10 volts )
low voltage at the white wire into the transistor box ?
(the output to the coils is normally off , so you can only check for consistent voltage at the input)
12.7 volts at the battery ... should be very close to 12.7 volts delivered to the transistor box .

Because the switching transistor is turned off there is no circuit, and thus no load. While your volt meter does create a circuit the LOAD is so small you cannot see any VOLTAGE DROPS in the circuit. For all practical purposes the volt meter reading you get, where the wiring harness delivers electricity to the electronic box, is meaningless.

To actually see what voltage the box is getting you need to create a circuit.

For a POSITIVE GROUND application this requires you to run a jumper from the point where the wiring harness is connected to the box's white wire to the coil connection where the box's black wire is connected.

For a NEGATIVE GROUND application this requires you to run a jumper from the coil terminal where the box's black wire is connected to ground.

In both conditions you have now created a circuit. By creating a circuit you will be able to measure any VOLTAGE DROPS created by bad grounds, high resistance connections, fuses, switches or battery.

It would be the same if you had points, and they were closed. Now measure the voltage. If across your battery you get 12.6 volts you should get near that at the coil. If it is 12 volts or less you have a problem in the wiring or a bad battery. You should also read near zero volts at the coil's grounded terminal. If you read voltage at the grounded terminal you have a bad ground.

And as for grounds the coil must have a connection with the engine (exception is dual lead coils. They create their own circuit). Do not assume that the engine is properly grounded to the battery!!!!! If your frame is powder coated do not assume your engine is properly grounded - no ground - no circuit - no noise!

Last edited by John Healy; 06/28/20 7:04 pm. Reason: changed to transistor - thank you nick
Re: Boyer Bransen B25
Treforissa #814241 06/28/20 12:24 am
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John, i find your terminology rather strange here, in my head a 'Switching Diode' is a Thyristor, which
is also termed SCR (Silicon Controlled Rectifier) These devices are not present in a Boyer unit, in fact
they were only used in CDI type ignitions as far as i know. The output of the Boyer is a Darlington Transistor
which is normally just referred to as a transistor, this applies to 95% of this type of older style units. Later
ones may use either MOSFET or IGBT output devices, but not SCRs. The snag with a thyristor in this
application would be it's switching off, i suppose a GTO type could be used but they are rare now, largely
replaced by IGBT's
Please don't think i'm having a dig in any way, but some people may find your reference to a switching Diode
confusing and/or misleading.

Re: Boyer Bransen B25
Treforissa #814327 06/28/20 7:09 pm
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I changed to a transistor, BUT did you get the point I was trying to make. Measuring the voltage at the box, without a completed circuit, and thus a load on the circuit, is meaningless exercise.

Re: Boyer Bransen B25
Treforissa #814371 06/28/20 11:29 pm
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Absolutely John.

Re: Boyer Bransen B25
Treforissa #814407 06/29/20 6:31 am
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retard the magnet some more... turn it opposite the direction of rotation. once it starts and runs use the strobe to fine tune the plate. the instructions say gotta be up to 5000 rpm to set the full advance but I think I used to do less, then drive it and see. modern fuel has no lead so the final advance that woks may be less anyway. whatever, they work great on the unit single. I could start my B44s, B50 and B25s wearing my bedroom slippers


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