Ignition Timing Question


4 replies to this topic
  • wweagleflyer

Posted April 28, 2013 - 07:10 AM

#1

This may be a dumb question, but I can't find the answer I am looking for. The question is this: How does the ignition system know which time to fire when the piston is at (or near) TDC? I assume that the timing of the magnetic pulse from the keyed flywheel magnet tells the ignition system when the pistion is at (or a few degrees before) TDC, but how does the ignition system know when the piston is at the top of the compression stroke (when a spark is needed), and when the piston is at TDC after just finishing the exhaust stroke? The crank shaft and flywheel are in the exact same position at both times.

Another way of asking this question is: What times the ignition system to the timing of the valves? I suppose one solution is to say that the ignition system fires twice per cycle - once when needed, and a second time at the top of the exhaust stroke. That doesn't seem like it would be the right answer.

Thanks

  • grayracer513

Posted April 28, 2013 - 07:34 AM

#2

I suppose one solution is to say that the ignition system fires twice per cycle - once when needed, and a second time at the top of the exhaust stroke. That doesn't seem like it would be the right answer.


Oh, but it is. The ignition is triggered from the flywheel near TDC on every revolution.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • wweagleflyer

Posted April 28, 2013 - 07:45 AM

#3

Thanks for the reply.

Firing twice per cycle means that the ignition system has to supply twice the current as needed, which I would think leads to an unnecessary oversizing of the stator. I guess any weight savings by having a smaller stator are more than offset by the weight, cost and complexity of having a sensor on one of the cams to detect valve position?

  • KTM_Pat

Posted April 28, 2013 - 08:28 AM

#4

It is.... what it is....

Just a precise high speed hall sensor.

Edited by KTM_Pat, April 28, 2013 - 08:29 AM.


  • grayracer513

Posted April 28, 2013 - 10:15 AM

#5

The current is only twice as much on a total wattage per minute basis. Otherwise, the current requirement per event is no different, and doesn't require any extra "oversizing" of the stator. If anything, the flywheels in these are ridiculously small, if you ask me. The gas cap is almost bigger.

Posted Image





Related Content

Forums
Photo

1998 yz400f will not idle. by trolley


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  32 replies
Forums
Photo

YZ450FX OR YZ450F by MESSMAKER


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies
Forums
Photo

Should I buy this bike? help....... by Numsa Hul


Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies
Forums
Photo

2016 YZ450 by CaptainKnobby


Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies
Forums
Photo

05 yz450f not fast enough by RedeyeYZ


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.