Timing Advance

Discussion in 'Electrical' started by BigBlue, Jan 24, 2013.

  1. BigBlue

    BigBlue Active Member


    I have always wondered how the timing is advanced with the Happy Time/China Girl engines. I haven't seen a post on how the timing is actually advanced. I think the timing advance has something to do with the shape of the magneto.

    Here's a video posted on YouTube demonstrating timing advance on a Happy Time/China Girl:

    I found an article on Silicon Chip Online about CDI modules for small engines written by John Clarke. The kit is sold by Jaycar of Australia:


    Figures 3 and 4 in the article explains how a stepped trigger coil can advance the timing of the engine. The stepped design is not the shape of the coil in the Happy Time/China Girl engines. However, it is the shape of the magneto. Rather than stepping magneto coil, the Chinese shaped the steps into the magneto to get the timing to advance. The engine case is just too small to fit a stepped magneto coil.

    Here's a picture of a magneto and see the stepped design:

    Of course I don't know if what I am saying is true or not. I am electronics illiterate and mechanically declined. Maybe I am seeing something that isn't even relevant.

    Maybe someone with more experience can contribute.

    AKA: BigBlue

  2. Fabian

    Fabian Well-Known Member

    Don't even worry about that stuff.
    Get yourself a Jaguar CDI if you want to advance or retard the ignition timing. It's a good system and it works reliably.
  3. Purple Haze

    Purple Haze Active Member

    These single cylinder 2-strokes need a timing retard at high rpm. The Jaguar CDI is the best thing on the market now, but if you insist on fooling around with the mag, there are offset keys available to move the position of the magnet, advancing or retarding the timing. The main problem with this is it is fixed at all rpm's, not the hot ticket. The Jaguar CDI retards the timing in increments based on rpm, and has several settings available to finetune the amount of advance. Jaguar has written some excellent theories on the subject; go to his site and read up, he is a lot smarter on this than I, plus he has some excellent tips on exhaust mods.
    Last edited: Jan 25, 2013
  4. SuperDave

    SuperDave New Member

    Okay, here's my deal. I have a GT5 Super Rat, and due its integrated magneto/coil, a Jaguar CDI setup won't work for me, I'm locked into what Grubee built for it. Where do I get offset keys? There are a number of manufactures & distributors for offset Woodruff keys, but without a micrometer or a precision dial caliper, I've no idea what size to get. Any suggestions?
  5. Fabian

    Fabian Well-Known Member

    The GT5 Super Rat makes things a bit more tricky. Having said that, i would love to get my hands on a Super Rat and start messing with it...
  6. HeadSmess

    HeadSmess Well-Known Member

    the advance curve is a BYPRODUCT of the cdi operation.

    as the magneto spins faster, its voltage peaks higher. the voltage increases faster with rpm, its not a lineal increase. the trigger point is at a certain voltage. voltage is number of magnetic lines cut per second. cut the same number in half the time, create twice the voltage...etc etc.

    at low rpm, when the voltages are quite low, the time between the "zero point" and when the thyristor is triggered, is quite long.

    as the rpm increases, the voltage gets higher. the time between zero point and the trigger voltage is less. this is ADVANCED.

    this time keeps decreasing until the magneto core and windings reach saturation, at which point, the curve levels out and stays relatively flat. you cant build the voltage faster than the laws of nature allow!

    the addition of timing capcitors etc in the trigger circuit "delays" the trigger pulse, increasing the time between zero crossing and trigger voltage level, or RETARDING at higher rpm.

    post a pic of the new intergrated cdi magneto, please! first ive heard of them!

    with any luck, the bolt pattern is the same, all you need to do is swap the magneto coil, and either buy a jag cdi for $70, or make the circuit for less than $10. either way, you still gotta buy a small $10 dollar pitbike coil :)

    instead of offset woodruff keys... try getting the magneto slotted out wider, and drilling a hole through the magneto, that penetrates through the key slot. tap and insert a grub screw from either end. when they both press against key, magnet is locked in that position. loosen one, tighten the other, and advance or retard from the original point :) then stick a second grub down each hole to lock the first grubs :)

    not sure how the laminated magnets will go with drilling and tapping :) obviously i havent done this, ive only thought about it :)
  7. HeadSmess

    HeadSmess Well-Known Member

    oh...and regards "notching" or "stepping" the leading edge of trigger magnets... its usually less than 1mm. the HT magnet is about 4mm or so. has NOTHING to do with advancing or retarding timing(as far as im aware, mind you). more to do with generating fast rise time voltages, with a large "null" or zero crossing (no voltage produced) that ensures a positive, clean trigger pulse. gives time for things to discharge, reset, cool down... dealing with microseconds here!

    the CDI operates in a completely different fashion to one that has a separate trigger coil, where that idea is used effectively.