The old "men" in the GL lineup ('75, '76) are mostly forgotten about and sure seem to be small by today's standards, but you can have a lot of fun playing around and hot-rodding them. Their engine layout just begs for all sorts of hand-made goodies, and the basic boxer layout is ready made for doubling, and even tripling output. My final grade from GM Institute in 1978 was to pick an engine and squeeze 3hp/ci out of it without pressurizing it, and on pump gas. (actually, pump gas included Sunoco 360 and 104 av-gas!)
CaptainMidnite wanted to know about my "single-fire" ignition, so here's the whole story of this project, starting with the ignition.
The goal was 180+hp, but that means lots of fuel/air and higher cylinder pressures, which means much higher spark voltage. I've never been a fan of the usual double-ended coils. First, trying to contain that much voltage in such a small package is just asking for a short lifespan and limited output. Also, If your plug gap on each plug is .050", then the coil is looking at an equivalent of .100". That requires a lot of push to jump. As the rpms climb, so do the spark voltage requirements and those stock coils are just very limited.
My solution was to use the points box as a base for fitting a custom distributor. In this case I used the optic pickup from a Toyota pickup truck, a cap and rotor from a Fiat 850, and an old Heathkit CDI unit driving an Accel coil. Had to machine up adapter rings to mount the pickup, the cap and another adapter to hold the rotor. The slotted rotor from the pickup system only need very little material removed from the inside to press tightly over the stock point cam.
After the rest of the work was done, quite a bit of dyno time was spent tuning the advance using different springs. Ended up ruining several sets of stock springs by heating them slightly to weaken them. That's kind of an art, and I'm no artist! My dealer looked at me kinda weird when I kept coming in for advance springs. He said he had never sold any others to anybody!
I really don't know what a stock 1000 engine is capable of doing with good coils and everything in tune, but mine seemed to stumble starting around 8200rpm. The new ignition was smooth all the way to 10,500 which is where I detected some valve float. And, this is where the rest of the story begins about the other mods to this bike. But, first, just a couple more issues with this distributor before anybody runs out to try this!
Notice the 90 degree plug towers on the cap. Naturally, they had to be to clear the rider's left foot. Still, my foot only cleared them by maybe 1/2". That all worked well under normal conditions, but when you roll the throttle on hard and rpms climb, so does the spark voltage. I lost count how many times I got bit hard not paying attention to that fact! Eventually moved the peg back 1" and shortened my shift lever 1". That was fine, except for riding in rain! Had to hook my foot on the rear peg and be sure I wasn't "on it" when I would slide forward to shift it. Not exactly a rider-friendly setup! Again, eventually I made a mica shield to block my foot from the wires! The Accel coil and higher spark voltages took their toll on the Fiat's cap and coil. A distributor driven off the front of one of the cams and sticking out forward, and having a larger diameter cap would work much better. Even a GM HEI cap/rotor, using just four towers, would be much better, but what did I know back then?
That's the distributor part of this build. More later. BTW, it eventual put out 182hp at the output shaft.