home brew ignition question ( anyone built one )

Has anyone built thier own ignition system using auto parts for the Commando . Such as some have done for the xs650 ?
I'am looking to install a new ignition system on my 73 750 commando. So now trying to figure out which direction to go . I know I can just buy a boyer or . However it would be nice to use parts that I can easly replace by going down to the parts store . That and like most I enjoy doing things like this .
Oh so far on the 73 I've installed a rebuilt 72 engine ( the 73 was missing the head & cylinder when I found it ) . Just rebuilt the carbs now need to fire the beast up for the first time .
And then on to the 72 with a mojave tank , oil in frame ,single carb, 2 into one pipes , drum brakes , solo seat with a cafe fairing .

thanks

Dr mac

The problem with DIY is the mechanical trigger and advance mechanism. Any auto parts ignition module with built in advance won't be right for the Norton. Those without it require you to handle that part yourself. Some people adapt the Lucas AAU and cam with some sort of magnetic or optical trigger, but then that becomes the weak link in the reliability chain. The GM HEI module with a home made reluctance trigger is one way to go.

I designed and built a CDI system for my Norton using an optical interrupter module and a "blade" attached to the stock points cam many years ago. It left me stranded due to mechanical failure of the trigger, so I gave up. Then I discovered the Boyer and never looked back.

I hope you have some electronics knowledge :wink: If you are willing to put up with a mechanical advance, I could send you a circuit diagram of a simple ignition that does away with the points, if you want to do some research for yourself, this site http://www.transmic.net/en/home.htm has lots of informtion on building a mapped CDI using a PIC. While it it nice to build your own, the state of modern electronics and manufacturing methods have gone way past the homebrew basement workshop and it could just be getting old, but being stranded because of a faulty electrical / electronic device does not seem like fun to me anymore :lol:

I haven't tested ALL ignition systems, but I know a few, this is the latest I have personal experience on: http://ignitech.cz/english/aindex.htm I have just installed a CDI unit on my Yamaha RD400 and it is a slick unit, fully programmable, well made, rugged.

Jean

I have built several homebrew ignitions with automotive parts. The old Chrysler ignition module works well with the
Chrysler pickup unit mounted to the original points plate and a reluctor mounted to the points cam. I used this setup for many years and even removed the seal behind the advance unit so it was bathed in oil to keep it from wearing and sticking. The GM hei module causes problems at the slow firing rate on a two cylinder engine because it has a built in dwell limiting function that will kick in at low speeds and cause an extra spark at the wrong time. I have also used the VW rabbit module and hall sensor with success. Jim

I also had good luck with the Chrysler module on a bike, but recently I had one I did a while back with a Ford one fail. Now that they are so good and easily available the only reason to do one is fun.

Way back in the 70's they made cap discharge units that connected to the points. It used the original points as the contact, but would not pump all that coil current thru them, so they would last a lot longer and not pit from the spark. They produced a much hotter spark, so you would have to make sure the coil and the high tension wire to the plug will stand up to the voltage. I wonder if these are available any more? That way you could use the Norton mechanical advance, original points and just have a much hotter spark and longer lasting points. They did suck up about 1 or 2 amps so that would mean your alternator and voltage reg would have to be in tip top shape.

Dave
69 S

The main disadvantage of the points ignition is the wear of the rubbing block and the innacruacy of the mechanical advance so even having a hotter spark with a CDI triggered from the points is a waste of time and money. I built my own pointless ignitions in the seventies using either an optical trigger or a hall effect but retained the mechanical advance unit, I would say my ignitions performed as well as a Boyer, but the lure of one less mechanical device and lifestyle choices led me away from building a finished product.

Time marches on and these days, only a programmable unit is worth considering, whether buying or building. If you want something dead simple that can be fixed anywhere in the world, stay with points, if you want improved points, Per in Sweden has a modified cam profile which provides less dwell so less current draw but more than enough for a good spark.

Jean

I have a school book somewhere here with how to build the cap discharge unit. I've not done that for many years for the same reason Jean mentions as well as wear inside the cam bushing tends to make them sloppy.

Here is a picture of the AA unit Per Gadd has on his Norton, it was made for him by a machinist in Sweden, along with a modified cam profile, there is a brass bushing between the moving pieces to tighten up the tolerances.

Jean

Nice! I had to have something similar done in the late 70s but I had to pay a machinist.