Wedgetail ignition install on a 73 R90S. Long drivelling post.

[alocky]

I figured I'd post this up here in case anyone is considering doing something similar. For background, I bought my R90S out of QLD a couple of years ago with the intention of riding it back, although the wildly fluctuating borders meant I ultimately had it stuck on a truck after having it 'recommissioned' by a well known QLD airhead specialist. I was pleased to hear that it ran beautifully, and spent hours watching the short phone video of it idling in the shop as I waited for it to arrive.
When it got here, I discovered that it had previously been fitted with an aftermarket ignition system. This was an interesting solution using a pair of ferromagnetic pickups that were triggered by a magnet on an aluminium plate. Advance was still managed by the advance springs, and the plate had been screwed on so tightly the entire thing had cracked. It still ran, fortunately, but on riding the bike with any kind of enthusiasm it had a very nasty ping which I attempted to solve first by putting avgas in the tank, with increasing amounts of octane booster until it was running on a fuel almost worthy of a drag motor. It wasn't until I started playing with the ignition timing that I discovered the flywheel had two S marks under the strobe light about 5 degrees apart. Except of course it didn't, so finally I discovered that the two magnetic pickups in the plate where the points used to live were of the free-ranging variety, and basically moved about as they pleased, meaning the timing was not symmetric. So I chucked all of that out and reinstalled a set of points and the bike ran beautifully.
Fast forward, and I found myself in possession of a Wedgetail unit. After 12 months of trouble free operation I found the points gap had closed slightly and needed adjustment. Being of an astonishingly lazy disposition I resolved to replace these archaic things so I never had to adjust points again. Even better, after some discussion with the Wedgetail guys, I decided to replace the coils with a modern 0.7 Ohm unit, fed via new 15A wiring direct from the battery and switched via relay from the original system. The reasoning is sound. The spark from a modern ignition system is so big that it heats the air in the cylinder enough to operate the motor in the absence of fuel.
The installation is fairly easy, with the wedgetail brain sitting on two straps that hang off the bottom of the rear tank mounting rubbers. A brown wire with eyelet goes to ground, and if you were going to be a poor plebian with low performance 6V coils in seriesas issued by the factory, you simply replace the points wire with the black wire from the unit, pick up the switched power to the other side of the two coils in series with the green wire to the unit. Power is supplied from the ignition switch to the same terminal and life becomes better in every respect. Also cures ED, warts and pimples; as used in major hospitals.
For those of us who are better than this, you replace the two coils with your fancy 0.7 ohm Dyna unit, add a 15A wire to the coil switched by a 15A fused spotlight relay which is energised by the same green wire from the ignition switch, and pick the power up to the wedgetail unit off the 12V input side of the coil. Then the fun really starts.
Turns out, I had previously replaced the nasty corroded instrument lights with the fancy Katdash LED ones that makes viewing idiot lights a pleasure, and interesting phenomenon occurs (I see no reason why this might not also happen with the original lights). IN case anyone was wondering, the reason the alt light goes out when the engine is running, is because when stationary, the small amount of current flowing through the bulb energises the windings on the rotor enough to kick start the alternator's magnetic field. Over about 1500 rpm the rotor gets up to 12V and there is no voltage difference across the bulb so it goes out. When I turn off the ignition on my old bike with the fancy new system, this same 12V keeps the damn coil relay open and the bloody thing will run until the charging rate drops sufficiently for the relay to close. This can be instantly, or up to 5 minutes after turning the switch off, depending on how much of a charge the battery got. Disconcerting at best, bloody annoying in general.
There is a simple fix, putting a diode in the 'green with black tracer' wire that goes to the instrument lamp panel, best accessed where the loom coming from the motor meets the one from the headlight shell. Alternatively you could just bloody-well leave the thing alone and adjust the points every now and then. Performance wise - it starts a bit better, runs fine and certainly runs better than when the points had closed slightly. Girls smile at me more and kids cry when I stop next to them at the lights. Dogs don't seemed to have an opinion, but to be honest I think you'd need to see dynometer results to know how much improvement it makes - they do claim better fuel economy and a couple of horsies. Anyway - food for thought for anyone wanting to join the fat spark club.

[spacey1]

Good write up alocky...

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