???Riddle me this???

[Stoneman]

On a gt5 super rat it has magnets on one side of its magneto also on a small pocket bike 49cc it also only has one side

Now if we look at our the magnet, they make contact twice per revolution
On all these rev tacos they are showing 2 sparks per revolution

 

[crassius]

CDI unit has a full wave rectifier - collects both pulses from mag and combines for extra spark

 

[Stoneman]

CDI unit has a full wave rectifier - collects both pulses from mag and combines for extra spark

Now that makes sense, but how does it know to release it without points
The reason I ask is setting up these tachs (I know some don’t like them), if I set it to 1 spark per revolution it reads to high,

 

[crassius]

I'd suppose it fires when charge gets to certain point on the capacitor, or perhaps by rise-time of the voltage level

I'd look for a tach that hooks inductively to the spark plug wire.

 

[HeadSmess]

oh gawd, the cdi has been gone into in depth...

most CDI units use a separate trigger coil to fire the SCR as required.

the happytimes, like a few oddball motorbikes, doesnt.

it uses one side of the voltage waveform to charge the capacitor, storing it with a diode and SCR. lets say the positive going side of the wave.
the negative voltage triggers the SCR and discharges the cap into the coil&plug. its pretty damn smart if you ask me...

brushcutters and weed wackers and the like have two magnets as well...they are simply spaced very closely together on the flywheel, the coil being the pickup and CDI unit all packed into a neat little package (except for old brushcutters that have a separate cdi thingy tucked away somewhere....)

 

[Stoneman]

oh gawd, the cdi has been gone into in depth...

most CDI units use a separate trigger coil to fire the SCR as required.

the happytimes, like a few oddball motorbikes, doesnt.

it uses one side of the voltage waveform to charge the capacitor, storing it with a diode and SCR. lets say the positive going side of the wave.
the negative voltage triggers the SCR and discharges the cap into the coil&plug. its pretty damn smart if you ask me...

brushcutters and weed wackers and the like have two magnets as well...they are simply spaced very closely together on the flywheel, the coil being the pickup and CDI unit all packed into a neat little package (except for old brushcutters that have a separate cdi thingy tucked away somewhere....)

But wouldn’t that still mean two sparks per revolution?

The North Pole or what of the magnet passes the stator arms twice per revolution while the south also passes twice. If I understand you correctly the south is releasing the spark?

I’ve read some information where there is 2 strokes that fire this way (not digital coil or something like that) but they are just rare comments calling it a wasted spark like on some 4 strokes.

 

[HeadSmess]

no.

theres only one positive and one negative wave per revolution.

north passes upper pole, as south passes bottom pole. thats positive say.

180 degrees, and the situation is reversed.

go and look at how an AC generator works. its perfectly self explanatory.

one full 360 degree wave per revolution. one spark.

fourstrokes have exactly the same setup. one spark per revolution (except for the few oddball ones that used a cdi trigger on the camshaft, like the early CDI models of the honda CT110. that still used a centrifugal/mechanical advance mechanism rather than part of the CDI itself working electrically. they simply replaced the points from the previous years model with a trigger coil. few years later the changed to a flywheel mounted trigger coil with the waste spark system, its easier.)

 

[Stoneman]

It’s got me baffled the settings on these tachs.

 

[HeadSmess]

easier to simply not worry about them