[Z50King]

ok, im wondering how a flywheel on an xr/crf/knockoff works.



i see that the pulse pickup is on the outside of the flywheel. what does that do when it comes in contact with the stator pick up? and what does it do spinning at 1:1 with the crank?



what does the stator charge? where is that charge held before it goes to the coil and is sent to the spark plug??



and how does an irk work?



or do i have it all wrong???



thanks guys

 

[themountain]

Are you asking seriously??? :lol: :lol:

 

[Z50King]

yes



do you know?

 

[umka]

as far as i know but don’t take as gospel.



the sensor is a hall effect sensor which detects the change in magnetic polarity. the sensor and fly wheel don’t actually touch so there is no wear and tear like in points systems. there will be a polarity spike when the little square piece on the flywheel passes the sensor and this is what it detects. yes 1:1 as i is directly connected to the crank.



the charge is built up and held in a capacitor before being set into the setup coil. that is why it is called a cdi, capacitor discharge ignition.



irk still uses a cdi so still a capacitor hold the charge till the spark fires and still uses a hall effect sensor to determine when to fire the spark. the flywheel is just a lot lighter and smaller and therefore takes less energy to spin up and spin down.



how that answers ur question

 

[Z50King]

ok, so why doesnt the spark plug fire every rotation of the crank? its 1:1 with the crank, but the cam shaft is 1:2 with the crank....



does the irk rotor have a little magnet thing on it? i ordered one so i guess ill see soon....

 

[arlindsay1992]

It fires at the top of the compression stroke AND at the top of the exhaust stroke. Just doesn't matter. Makes it simpler I guess. Just fires twice as much as it needs to. Doesn't cause any problems.

 

[Z50King]

are you sure?? because with the rate at which some of these heads scavenge, why dont they backfire??

 

[Kurlon]

These are not 'TRUE' CDI ignitions, the charge is transfered to the coil, the spark box just colapses the charge to ground (similar to a points setup) to generate spark. There isn't anything in the CDI building up a spark pulse to fire against the coil to generate a spark event. Basically, the spinning flywheel builds up an ac current, and runs it through the coil. Because it's 'gradual' it sets up a low voltage in the secondary, not enough to spark. The CDI comes in and quickly ties both sides of the coil to ground, cutting voltage to 0 very quickly. As the built up magnetic field colapses, it induces a very high voltage event in the secondary coil, which you utilize as a spark.



The bikes fire every rotation as the spark box has no way of knowing which trigger events from the stator pickup are on the compression or exhaust stroke. AKA it's a wasted spark setup. CT90s and 110s that drive the CDI pickup off the cam do not waste a spark and only fire on the compression stroke.

 

[Z50King]

oh ok



i understand it kinda.



so when the pickup passes the little piece on the flywheel, thats when it sparks??



and is there a piece of metal on the outside of the rotor in an irk setup? i have one ordered and am just wondering....

 

[Kurlon]

The metal going by the sensor generates a pulse to the spark box. The spark box notes the length of the pulse to determine RPM. (Slower the flywheel moves, the longer the bump is under the sensor, longer pulse, lower rpm.) It does a lookup, X RPM = Delay spark Y fraction of a second from the trailing edge of the pulse, colapse the coil, poof, spark.



The 'bump' on an IRK flywheel is a piece of ferrous metal within the alu rotor. There isn't a visible bump, but you can see the spot where the ferrous metal is when you look at the flywheel as it's a different color. Same rules apply, the sensor 'sees' that bit of metal as it whizzes by and signals the spark box accordingly.

 

[Z50King]

dang i didnt know the box did all that! thats crazy!!



its amazing that that little sensor can detect a time period that short and especially when it gets going that fast!



thanks guys....

 

[fiddyking]

jus think how fast the computers work on a F1 car when its revved at 18,000 rpms

 

[Z50King]

yeah