Electronic ignition problems.

[bubbles]

My 1978 80/7 has had a Boyer Bransden electronic ignition system on it for the past 31 years and 130,000 miles. I have borrowed Pastymans xenon timing light (thanks Tony) to check the timing as Rob Farmer said at the Wee..kend it sounded on tickover like it was a bit out. Anyway whatever I do I can't get it right at tickover and 4500rpm. If I set it correctly for tickover on the S mark in the crank case hole, then at 4500rpm the F mark has not appeared and I can still see the bottom of the S marks if I look from below towards the top of the hole. So at the moment it is set advanced on tickover (800rpm) with the S mark just starting to appear from the top of the crank case hole if the tickover fluctuates below 800rpm, which it tend to do as this makes the tickover a bit lumpy.
So the question is has something happened in the magic box of electronic tricks (transistor box) that must alter the timing depending on the rpm as the auto advance unit is removed with this system?
Should I get a complete replacement timing system? http://www.motorworks.co.uk/bmw/pro..._15_20_IA_40&header_text=&header_text_image=0 I really don't want to go back to points again.

 

[Greg Masters]

I know shag all about airheads, but if this were a car of a similar age I would suggest that either:

• the ignition advance bob-weights have seized, and/or ...
• the advance springs have broken

Greg

 

[SJRoome]

Hi

I had a Boyer Bransden briefly on my R60/6 many years ago and I had exactly the same issue. I contacted Boyer Bransden and the unit was performing exactly as designed. It did not advance the spark as much as the mechanical system.

It is intended that you set the timing to the F point at 4500 revs and accept the greater advance at tickover. Personally I did not like what this did to the feel of the bike (lower torque at low revs). After a month I sold the Boyer Bransden and fitted a points assistance system that used the mechanical advance.

Steve

 

[Rob Farmer]

Hi Geoff,

I was going to reply to your PM. Being a bit slack at the minute.

We had exactly the same issues with the analogue unit on RichC's R90/6. Rich bought a Boyer microdigital to replace it and it's made a hell of a difference to the way the bike runs.

I was curious how yours turned out when you posted about setting the ignition. The analogue units clearly do not perform well.

 

[Rob Farmer]

I know shag all about airheads,

Clearly. There's no advance retard weights with a boyer ignition.

 

[Greg Masters]

Clearly. There's no advance retard weights with a boyer ignition.

How does the stock ignition advance?



Greg

 

[Rob Farmer]

How does the stock ignition advance?



Greg

With an Advance/retard unit but the Boyer replaces the ATU and does it electronically.

 

[Greg Masters]

.... and does it electronically.

or not.

 

[bubbles]

Thanks Steve and Rob that explains a lot. So is the Boyer Bransden system now sold by Motoworks (see link in OP) the improved or digital one, cause it looks just the same as the one I have apart from the colour of the transistor box is red and black on the one I have?

I still have the original box mine came in, does this make it collectable .

 

[bubbles]

Thanks also to Greg for trying to answer my question, it's always good to get a response straight back in those dark moments when its all going wrong

Even if it is the wrong one .

 

[Rob Farmer]

The Red one is the Microdigital.

Snowbums site has some info on the early Boyer (Yours) http://bmwmotorcycletech.info/Ignition.htm

Basically says " The early Boyer models also have an ignition curve that does not well match the Airhead engine requirements. In particular, the early Boyer had an ignition curve that was slow rising and kept rising, there was no practical limit....the ignition would continue to advance with increasing RPM. "

Are you going to treat yourself to a Microdigital Geoff? After 30 years of running your old one I think you've had your monies worth

 

[Rob Farmer]

Thanks also to Greg for trying to answer my question, it's always good to get a response straight back in those dark moments when its all going wrong

Even if it is the wrong one .

 

[bubbles]

Are you going to treat yourself to a Microdigital Geoff? After 30 years of running your old one I think you've had your monies worth

Yes I think I probably will Rob, but it will have to wait till we get back from the Moto Piston Rally as have only just spent a couple of hundred pounds at Motoworks on Tyres and bits. Only 1 full week before we travel now. Taking the old R80 abroad for the first time in its life has certainly focused attention on getting all those little things that needed doing sorted.

 

[Steptoe]

Refit the bloody points.

 

[bubbles]

Refit the bloody points.

If I could stop the water getting in when fording I might be temped to do that.