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'''Two Stroke Ignition''' I helped a friend build an ignition system for his 3 cyl two-stroke engine last winter. It's for a snow mobile: * 1260 cc, 200+ bhp (9000 rpm, idle 1500 rpm) * Carburators * M&W CDI ignition box (4 channnels, 3 used) * http://www.youtube.com/watch?v=IES9tmpFWrs We used a 6-1 trigger wheel with a Honeywell GT1 Hall sensor : http://i27.photobucket.com/albums/c182/JonasNilsson/Lynx%201260/ResizeofCIMG0375.jpg I might get better pictures later of the trigger wheel mounted, here is the engine assembled, all machine work has been done by the owner/builder : http://i27.photobucket.com/albums/c182/JonasNilsson/Lynx%201260/ResizeofCIMG0428.jpg This setup has worked for us, last winter the snowmobile made 700 km. The only problem is starting it - our current method of triggering the ECU in combination with the pull start mechanism makes it tough! \\ Sometimes it will not sync to the trigger wheel and won't fire and start while the engine has momentum. Every pull only rotates the engine two turns, making it hard to get solid starts every time - even if you make a "good" pull that would've worked on factory three cyl snowmobile engine. \\ Granted, many factory engines have electrical starters but this is not an option on most racing machines and there is very little room for it on this one since the chassis is originally made for a two cylinder engine, not three. The stock ignition systems on these two strokes fire wasted spark, on every cylinder event, two cylinders do it all the time, and three cylinders at least while cranking/pulling. This is what we would like to do as well, but that will probably require a mix of changes in both the firmware and trigger system. One plan we have come up with is this : * Change the primary trigger to one that uses three teeth, one per cylinder event, and these are used as a simple trigger in "config A". This makes it possible to fire a single ignition output on each trigger event, the output connects to all three inputs on the M&W CDI box via diodes so that the three are only short-circuited at the ECU. ** There is no waiting to sync up with missing teeth or cam sync at this stage, the coils fire immediately and the engine should be much easier to pull start. * To avoid using up too much power in the ignition system, once RPM reaches 1000 rpm, we switch to config B which uses cam sync as well. This time three other ignition outputs are used to fire the coils sequentially. ** A misc output simply grounds an analog input in config A above 1000 rpm and in config B this output is always on. ** TableSwitch can watch misc condition without the "HW feedback" (maybe a constant-activated analog input still needed, but using up an output is not needed). It could be that simply changing from 6-1 missing tooth trigger to a 3+1 trigger will make starting better, easy enough to be satisfied. Why ? That also needs 1 crankrot, right ? Just +1 input. What is the opinion of the firmware experts on the options we have ? * There is a special mode (hardly used, only on some kickstart bikes) of coiltype trigger, when trigger pulse happens around 10-15 BTDC so spark can follow right away during cranking. ** Activated by igntdcdelay < actual ignadv AND low igntdcdelay configured (<40 deg IIRC, but probably only 6-15 deg makes sense). Do some benchtest for the chosen trigger before grinding. * There used to be a "watch both edges while cranking" mode for sectrig. Might be useful for 3+1 type trigger. ** So long (HALL) sectrig pulse might help a lot. ** this mode wasn't used at all for ages, and needs retesting for sure
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