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Posted by Rob Kleinschmidt on March 2, 2007, 3:10 pm
> Mark Olson wrote:
> > Rob Kleinschmidt wrote:
>
> >> I've got an '88 boxer with a funny BMW ignition design. The bike
> >> uses Hall sensors in combination with a centrifugal mechanical
> >> advance rather than just using fixed sensors feeding a black box
> >> electronic advance.
>
> >> The bike uses a wasted spark design, sending one spark
> >> to both cylinders on every revolution. This is what Harley
> >> calls "dual fire". Full retard is 6 degrees, with ~25 degrees
> >> advance and full advance at about 3000 RPM.
>
> >> What I'm wondering is whether it's possible to buy just an
> >> electronic advance unit and trigger the unit using the original
> >> Hall pickup with the mechanical advance disabled.
> >> I don't find anything on the market with a drop in sending
> >> unit and suspect that the original unit could be adapted
> >> fairly trivially, possibly with a swap of Hall transistors.
>
> >> Any thoughts on aftermarket black boxes that might fit
> >> the bill ? The mechanical advance is getting cranky and
> >> I'd love to stop fighting with it.
>
> > I don't know about an aftermarket unit, but you might look into
> > an OEM unit from another make with similar sized cylinders and
> > wasted spark. After thinking about it a little, even an ignition
> > unit from a big (400-650 cc) single cylinder engine should work
> > OK, too, the ignition module doesn't care whether the coil
> > secondary is dual-ended or not.
>
> > The biggest problem I see is getting a good match to the advance
> > curve, I'm thinking modern 4-valve combustion chamber designs
> > will probably have more total advance and may kick in at lower
> > revs than you want. Also it's going to be difficult to get
> > advance curve data without measuring it yourself.
>
> > A smart fella might figure out a way to fit a microcontroller
> > between the Hall effect sensor and the stock ignition amplifier,
> > but that could turn out to be a lot of work...
>
> Did you see this guy's page?
>
> http://www.stephenbottcher.net/BMW/R100T.htm
>
> Follow the links in the "March 2005" section here:
>
> Install an electronic ignition with alternator pick-up (Made in Germany)
> and 16 different advance curves (beancan is still installed, correctly
> adjusted and can be activated on the road with just one simple cable
> swap) . Here are the installation instructions in English.
Only problem with this is that it limits your ability to do
add an aftermarket charging system because it bolts to
stator plate. There are a couple of trick charging systems
that I think this unit precludes. It's definitely a candidate
though.
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