I've got a question on timing for anyone. Since the plugs in a commando motor fire at the top of each stroke, be it compression or exhaust, then hypothetically could you could cross the plug wires without having any noticeable effect on the running of the motor? I just had this discussion with a friend who says the motor would backfire, but I don't think he understood why... nor do I.
Timing question
- Thread starter Robb2014
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rvich
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I assume you have an electronic ignition with a wasted spark? Typically the 6v stock coils get wired in series with the EI. They do not get any signal for left or right like they do with the stock point ignition. It wouldn't matter which one you hooked to which cylinder in the wasted spark system. Points on the other hand, it will have you kicking and cussing. If in doubt, try it!
Russ
Russ
L.A.B. said:
Ahhh, thanks LAB, now things are making sense. I tried first startup after the rebuild last night but only got an occasional backfire out of the exhaust. When looking at the wiring diagram it's a little confusing which coil is which. I assumed the bottom coil on the diagram is the left coil as you're sitting on the bike. This means yellow black to positive on the left and yellow white on the right. If not then I've got it 180 out.
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Robb2014 said:
Presuming this is a '71 or later model 750?
The coil positive to points wires are normally black/yellow for the L/H coil/cylinder, and black/white R/H.
If you have a yellow/white (or white/yellow?) then something may not be connected correctly as 'white/yellow' (from the kill switch) normally connects to white/blue which goes to the ballast resistor, then a white/purple from the ballast resistor to both coil negative terminals
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AMend to checking which jug is actualy on the firing stroke by checking which valve set is open or closed just then, as everytime I've tired just putting a finger
over plug hole compression testing I've ended up frustrated pooppoo's 180' off.
Red nail polish now on the correct rotor mark to match TGIF on boots. [toes goes ins firsts]. On points wired 180' off you can switch plug leads to run with crossed eye'd looking connections. That AAU is a real bother to even seasoned mechanics.
Dual wasted spark can be up to 15% weaker its said on the side the spark must jump form hook to center pole instead of the easier way across. But runs same crossed or not.
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Just swap the plug leads and kick it in the guts ! I use a honda 12volt double ended coil with a Boyer control unit and pickup, so I never have the problem. But on older twins it often happened during rebuilds that the spark ended up on the wrong stroke. A loud backfire from the exhaust is usually the clear sign that the leads are crossed if the system is not of the wasted spark type.
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