Boyer Bransden ignition system first report.

[gtmdriver]

A couple of weeks ago, while I was sorting out an ignition problem, I also decided to change to a contactless electronic system. I chose to go with the Boyer Bransden unit, Kit 00089, which is listed for the CB400F and CB750F but, with advice from this forum, I assumed it would fit my 350F too. It cost around £130 with carriage.

Mounting the small electronic control box took most time but I finally fitted it under the frame below the seat nose using Ty-Wraps.





Fitting the rest of the kit was no problem. The whole points backplate is removed. The advance unit is taken off so that the springs and bobweights can be removed then it is refitted onto the crank. The Boyer Bransden unit has a built in electronic advance curve so the bobweights and springs are no longer needed.The circular circuit board replaces the original backplate and the magnetic rotor bolts onto the remains of the advance unit. The original wiring loom can be used but I made up a new loom as far as the connectors under the air filter box.





Like all aftermarket ignition systems the BB unit is designed to work with the stock coils. I checked these and found that they had a primary coil resistance of 4 ohms. I had suspected a coil fault so I was replacing them with new coils from DS Spares. Fortunately I also had the presence of mind to check the replacements which was just as well as they only had a 2.2 ohm primary resistance which would have drawn far too much current through the BB electronic box. After checking with BB I used a couple of 1.6 ohm ballast resistors, one in the power feed to each coil.






The initial set up, described in the instructions, gets the bike started then you can use a strobe to accurately set the timing using the full advance timing marks.

An interesting feature of the BB ignition is that, with two pick up coils replacing the contact breakers and TWO rotating magnets replacing a single cam lobe ALL four plugs fire together all the time

I contacted Boyer Bransden to find out the thinking behind this and they said

"There are a few reasons. Its more accurate, once its completed one revolution, the system will find a central point for sparking and that will never change. Because of this, it makes setting up much easier and can be done on any cylinder. It also burns un-burnt fuel ready for the next firing stroke which improves the running and emissions of the engine."

I have had the bike out a few times with this system fitted and it is a definite improvement over the old (and possibly a bit iffy) coils and contact breakers. It is smoother and more tractable at lower revs (probably due to the slower advance curve) and definitely pulls better at high revs too.

[AshimotoK0]

That pickup plate PCB is identical to the one fitted to my 400/4. It was fitted to the bike when I bought it in 1985 so that makes the design over 30 years old! Obviously 'tried and tested' then 

Ash

[Johnwebley]

That pickup plate PCB is identical to the one fitted to my 400/4. It was fitted to the bike when I bought it in 1985 so that makes the design over 30 years old! Obviously 'tried and tested' then 

Ash

 I fitted my BB about 1978 ish,

 and before that,about 1975 I had a unit fitted in an BSA A65 sidecar  racer,that was a different designm

[gtmdriver]

That's one of the reasons I chose the BB system.

They've been around along time.

[watty51]

I have fiited the same BB as yours to my CB350F and after the initial set up, described in the instructions, I got the bike started then used a strobe to accurately set the timing using the full advance timing marks.

Was just wandering what the rpm was it you set to accurately set the timing using the full advance timing marks.

On the front page it it quotes 4500rpm on the back page fig 2 it quotes 6000rpm.
But ive read it should be set at 3500rpm when you fit this system to a cb350f.

Any ideas

[K2-K6]

As far as I understand it, you just have to be in excess of the maximum advance point.

Higher revs than needed are not going to give you any error as it'll just stay at a fixed maximum.

So, if you set it at 4,500rpm, then run it up to 6,000 it shouldn't change at all as should have already peaked lower.  If that makes sense.

They are just setting a maximum absolute advance point to avoid going too far at redline. Anything underneath that is determined in their programmed strategy.