ignition timing adjustment methods

Discussion in 'Motorized Bicycle General Discussion' started by highseastravler, Mar 17, 2010.

  1. highseastravler

    highseastravler New Member

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    there are several ways of altering the ignition timing
    one way is the offset keyway good for about 4 to 6 degrees +or -
    then there is the "pole peice modification"
    where one grinds off the leading and or trailing edges of the pole peices and you getabout half
    the timing change from whay you grind need i say its a onetime adjustment method
    and last but not least cutting slots where the mounting screws go through the magnet frame
    altough this will allow only 2 or3 degrees change it may be all you need
    otherwise machineing a new rotor magnet assembly as the factory one is not a very strong magnet
    does anyone have any other good ideas on how togetbettercontrol of the spark in these china motors
    and about lighting unless theres a way to seperate the magneto and lighting frames i beleve that
    a 2 to 4watt charging circut with batteries is the best hope for good lighting

    .shft. .shft. .shft.
     
  2. AussieSteve

    AussieSteve New Member

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    That only sets the ignition timing for a particular rev range. There is no way to chang the amount of advance to correspond with rpm.
    Advance or retard to enhance a particular rev range and others will suffer.
     
  3. tommyboy1442

    tommyboy1442 Member

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    i have an idea, lets all send jim 5 dollars to aid in funding a billet race block, something he can possibly make for production, and then we can all buy good ol american, and then just ditch the chinee mota.....
     
  4. highseastravler

    highseastravler New Member

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    yes there is a method of making a variable rpm timing adjustment with the equippment provided steve but it involves a staggered gap at the pole peice on the leading edge
    and cuttingsome of the trailing edge off
    but ive also read in the 2stoke tunes book that small bore engines do not need much spark adance
     
  5. highseastravler

    highseastravler New Member

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    if timing is fixed for most power at lets say 6000 rpm its onlt 66 cc its not going to gripe much about kicking back when trying 2 start now if we had a500 cc bore id want a spark retarder just to get it started but after its running id return it to its advanced position
    we dont need much of a active advance curve just a good way to set the spark timing at all 2 would be nice because you dont have to be far off to loose peak power
    these chinas were built to run detuned and for $125 they werent concerned about much after that as a matter of fact im shure theyll last a lot longer running a little rich (4 strokin) not getting high revs and not getting so hot trying to put out peak power
    were working with popcycle sticks and elmers glue theres only so much that should be done lol
     
  6. sportscarpat

    sportscarpat Bonneville Bomber the Salt Flat record breaker

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    Rotating the magnet or stator with a slotted base seems like an easy way to do it. Is there enough room in there to even do this?
     
  7. highseastravler

    highseastravler New Member

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    i think the easyest is the offset keyway method
     
  8. exavid

    exavid New Member

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    It looks to me the timing is set for a good compromise between starting and running. There's no sign of kickback when starting and the engine will run up to reasonable rpms under load. It is possible to improve the engine and get a lot more performance out of it, but there's no free lunch. If you want the bike for reliable long term use the engine is pretty well set up as it is though a bit of cleaning up it's breathing wouldn't hurt. If the compression is raised by shaving the head, re-jetting and running a tuned exhaust the engine will definitely perform better at the high rpm end but that will reduce it's useful life. Higher heat and stress of higher power isn't going to make them last very long. That's without even considering the wisdom of riding at much higher speeds on a bicycle with barely adequate brakes. I don't mind peg scraping on curves and pushing my motorcycles to the limits of my ability but I don't think that's all that great of an idea on a motorized bicycle. The wheels, bearings, tires and brakes just aren't up to a lot of high speed riding.
     
  9. AussieSteve

    AussieSteve New Member

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    highseastravler, I think that you misunderstood me. I know there are a couple of ways to alter the fixed advance, what I meant is that it's not possible to get increasing advance with higher rpm.
    A pity, because that would make these little engines perform better.

    For fixed advance, setting an offset to the woodruff key is the easiest way, but as exavid says, they're already pretty well tuned for all-round performance.
     
  10. highseastravler

    highseastravler New Member

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    there maybe a possible way to gain the benefit of ignition advancement at higher rpm's
    if i knew a little more about the coil module "mostly when it decides to fire"
    since we have a single coil that both charges the cdi unit and determines when to fire it
    "i suspect that it does this at the zero crossing point on the wavefourm "
    that point can be minupulated possibly by modifining the pole peice desighn or in modifing the ground wire return circutry with a dc bias voltage if you have any ideas let me know
    but tommrrow im trying my staircase ramp on the leading edge of the pole peices and ck with timimg light i did check the stock unit and found timing dead still at all rpms
    if its a zero or triggering on the voltage as the second half of the sine wave starts to fourm
    some where right after the 180 degree point then a biasvoltage on the ground wire can both advance and retard the spark by several degrees a good start would be about 5% of the charging coils peak voltage
    i dunno but im gonna try it "also if it works then the bias voltage can be supplied by the lighting circut
     
  11. AussieSteve

    AussieSteve New Member

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    I came to a similar conclusion regarding the 'firing point', hence the 'stepped' rotor.
    I have an oscilloscope, but have never bothered to take a look at the waveform. It would be interesting, those steps on the rotor would give a stepped output voltage.
    My 'scope is a dual-trace, so I could observe both the magneto output and the HT lead to see exactly which point on the waveform the engine fires at.
    If battery power is available, signal processing of the original waveform to modify it's shape followed by an output driver to drive the CDI is another potential method of obtaining varying advance with rpm.

    Earlier, I shouldn't have said it's impossible to do this, but I really meant that it was impossible with the original system.
     
    #11 AussieSteve, Mar 17, 2010
    Last edited: Mar 17, 2010
  12. highseastravler

    highseastravler New Member

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    yes ive thought of that too one method was a controlled 360 to 355 degree delay line
    thattook a sample of engine rpm and pre calculated the timing for the next revolution "a way of getting a pulse before the pulse came along " but programming a pic controller isnt in everybodies toolkit the other would be getting a 3 wire cdi that has electronic advance circutry built in and hoping that there was enough energy "voltage current and timing"
    but i have been very dissappointed at the exciter coil output power "possibly due to that weak magnet they use
    so i was back at trying to trick the factory cdi into firing at a different time
    and comming to the conclusion that it must fire at the zero crossing point to not be affected much by varying rpm magnet gap coil voltage etc"
    the bias voltage on the ground return wire can be kept in check by back to back zeeners
    and filtered with a non polar electrolytic with the applied bias voltage comming from a half wave rectifier from the lighting circut with a transistors bias controlled by a pulse with circut
    but frist test would be to just put a low voltage battery in series on the cdi ground return line and see how much and if its consistant throught the rpm range the timing change
    then a graph can bemade so a controller circut can be built
    it should only have 3 connections 1 frame ground 2 lighting coil and 3 the ground return from the cdi
    the exciter wire can be left alone anyway theres no need to have to midify that wavefourm
    well off to testing hope we can beat the little black box lol
    ps i think theres only a rectifier cap darlington pair and coil in that thing "it cant be that complicated"
    theres defenantally no fancy timing circuts in there lol
    keith

    ps ive added a block digraphan

    [​IMG]
     
    #12 highseastravler, Mar 17, 2010
    Last edited: Mar 18, 2010
  13. highseastravler

    highseastravler New Member

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    im hoping to get some better info but this is what i beleve is inside the black box
    added i put 12v + bias on the ground side of the cdi unit and got about 5 degrees advance at idle
     
    #13 highseastravler, Mar 18, 2010
    Last edited: Mar 18, 2010
  14. exavid

    exavid New Member

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    The diagram looks right to me, a brief description of how the circuit works might be of some use to those who aren't familiar with a CDI system. The capacitor is charged through the diode on the positive half of the sine wave coming from the magneto coil. At this point the "zero crossing trigger" which is an SCR (Silicon controlled rectifer) is an open circuit from the capacitor to the ignition coil. When the negative half of the sine wave appears at the top of the diode it prevents the capacitor from discharging back into the magneto coil. At the same time the reversal of the magneto polarity voltage at the SCR triggers it so that it suddenly changes from an open circuit between the capacitor and ignition coil to a closed circuit. The sudden pulse of current is applied to the ignition coil which is actually a transformer stepping up the voltage from the magneto to a high enough value to arc across the spark plug.
     
  15. highseastravler

    highseastravler New Member

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    i do know i have used the other half of the sinewave for lighting and even under heavy load the engine continues to run the only problem is there still isnt enough power to run more than a small flashlight type bulb or a small cluster of led"s maggs and lighting coils shouldent be mixed together lol so the battery charging the lighting circut seems like the best brightest lighting method
     
    #15 highseastravler, Mar 18, 2010
    Last edited: Mar 18, 2010
  16. AussieSteve

    AussieSteve New Member

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    PICs are the most important tool in my toolkit.
    You read my mind, Keith, that's exactly the method I was considering. I have a range of 20MHz PICs here and all the junk to go with them, along with PCB design software etc to etch my own boards.
    I'm getting more interested, at this point.


    I thought about fitting a hall-effect sensor and using a real CDI, but as you point out, not enough energy without a battery and charge system.
    I'm in the midst of putting together exactly that for my bike - a 100W DC motor (generator) into a regulator and 12V 5Ah battery. I'm powering the generator from my shift-kit jackshaft.
    The drawback is that the battery carries all of the load when the bike is stationary.
    It'll still give me enough for good lighting and accessories, (like a real ignition system).

    The bias idea sounds like it could work, but a fair bit of current could be needed. It'll be interesting to hear how you go.
     
  17. highseastravler

    highseastravler New Member

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    ok ill try to build a volt/rpm/timing change graph i do beleve that the advance will not remain consistant as the voltage rise/fall ramps steepen at higher voltage/rpms
    i teally like your idea of building a higher power alternator setup to get 12v at "many amps"
    then lighting and possibly a old gm cdi unit could be used for a hot blue spark that can blast away carbon and run into many thousands of rpm's if there was a good 100 watt 12v scource the possibilities "oh the possibilites" im going to get me a pic programmer someday soon. as i grew up when there were still vacum tubes in televisions "not just the crt lol
    i use my mb to do a 40mi commute weekly and keep it on the deck of my sailboat
    i have found a very good bike for the kits i dont know the manufacture of them but they were made for the new york city package delevery bicycle guys "heavy axles" "thick rims" "heavy 12ga spokes" and hardened gears and chain
    tried to getit off the guy that owned it but he wasent budgin lol
     
  18. AussieSteve

    AussieSteve New Member

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    You're probably right about an inherent change in advance with RPM in the stock CDI. It definitely won't stay at precisely the same amount of advance. I suspect that it might even decrease advance very slightly with RPM.
    I'll bet, though, either way, that it's far from an ideal advance curve.

    We might be similar ages - I was around before solid-state technology got going.
    (I'm 51, born 2 years after B&W TV first started in Australia)

    Do get a PIC compiler and a programmer, you won't regret it.
    If you can make PCBs, there are quite a few free programmer designs on the web and plenty of free compiler and programming software.
    Atmel micros are the rage these days, but the older PICs are good for most things and cost virtually nothing.
    (Good fun, too.)

    Regarding my generator, although it's a 100W motor, as a generator I'll be pulling an absolute max of about 50W out of it.
     
    #18 AussieSteve, Mar 18, 2010
    Last edited: Mar 18, 2010
  19. Harry_from_Germany

    Harry_from_Germany New Member

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  20. highseastravler

    highseastravler New Member

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