Question Cdi - Inition Coils Vfr 750 F RC24 '86

Discussion in '1st & 2nd Generation 1983-1989' started by sider, Dec 10, 2017.

  1. sider

    sider New Member

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    Hello. I write my first post on the site, so I beg you to be lenient; ...) My name is Danilo and I write from Italy. I am looking for information on the ignition system of the vfr 750 f Rc24 1986 (to understand, the model with two pickups and the campulse on the front camshaft), and specifically I would like to know if anyone has ever tested the ignition coils to verify the direct current that the control unit sends to it when the starter is pressed. According to the honda technical manual, the only check to be made is that of the impedance, while from vfr 800 onwards, the check on the technical manual honda is based on the peak of direct current that must be at least 100 volts. I therefore wanted to know whether even in the RC24 the DC current peak test is valid and consequently if even on the supply cables of the RC24 coils one must have at least 100 volts. My Vfr has some serious problems that I can not solve and currently I mount an electronic control unit (bought second-hand) in England. The problem that I find is that on the cables of the front coils I have 48 volts peak, while on the rear ones I have 52 volts. If even the rc24 must have 100 volts, then I found the problem.

    PS: Sorry for my bad English

    Thanks in advance ;)

    Dani
     

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  2. GreginDenver

    GreginDenver New Member

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    In your pictures it looks like you have built a Peak Voltage Adapter and you are using it along with your multimeter for testing the coils.

    Are you certain that your Peak Voltage Adapter is properly constructed? Are you cranking the engine long enough to fill the capacitor in the Peak Voltage Adapter? Or is it possible that the capacitor is discharging at too high a rate and thus never reaching the true reading of your motorcycle's coils?
     
  3. sider

    sider New Member

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    You've got it: it's a built-in Peak Voltage Adapter. I installed the components that advised an experienced guy in electronics and I tested the adapter on my vmax1200, using the same battery. the vmax in a few seconds from peak values above 110 volts. the vfr does not reach 60 volts. I would just like to understand if even the old vfr rc24 must reach 100volts
     
  4. GreginDenver

    GreginDenver New Member

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    If I was trouble-shooting this problem on your vfr 750 f Rc24 1986 I would want to reduce the number of variables in the test.

    If I was going to perform the coil test that you are attempting I would want to guarantee that the motorcycle's wiring harness system voltage was a solid 12volts with a lot of cranking amperage available. I would not rely on just the motorcycle's battery for this test because during cranking battery could be low on voltage/amps and that would greatly affect the amount of coil charging that can occur during the Dwell Time Period commanded by the Honda Electronic Control Unit. The Electronic Control Units in older vehicles do not compensate the Coil Dwell Time Period for lower battery voltages, which can result in greatly reduced coil charging before discharge to the spark plug.

    A drop in voltage level in your motorcycle's wiring harness during cranking to perform your test may be causing the extremely low coil discharge readings.

    Before testing your coils with the Multimeter and Peak Voltage Adapter I would connect jumper-cables from a car battery to the poles of the motorcycle battery to guard against a drop in voltage supplied to the coils during cranking (the car engine must not be running while you have the car and motorcycle connected).
     
  5. sider

    sider New Member

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    [QUOTE = "GreginDenver, post: 577046, membro: 32885"] Before testing your coils with the Multimeter and Peak Voltage Adapter I would connec [/ QUOTE]

    Look, to test the CDi using this 65 amp battery. Can deliver more than 13 volts and I repeated the test a few minutes ago, after having loaded it to the maximum: the result is that nothing has changed and despite having 13.5 volts on the wiring, during the test I managed to reach 54 volts at most.

    These are the other values I have detected
    Campulse > 1.5volts
    Pick up cylinder 2/4 > 4 volts
    Pick up cylinders 1/3 > 3 volts
     

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    Last edited: Dec 10, 2017
  6. GreginDenver

    GreginDenver New Member

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    yes, I was just concerned, you obviously know what you're doing. I think your test results are accurate.
     
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  7. sider

    sider New Member

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    I'm sorry, mine did not want to be an "arrogant" answer. as I wrote, I have a bad English and probably write in a way too "edgy". I thank you anyway for the help. if you find out that even the RC24 ignition coils must receive at least 100volts, please let me know :)
     
  8. squirrelman

    squirrelman Member

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    if you're having spark problems, you need to test pickup coil resistances too.

    for good sparks each coil must get battery voltage (with key ON) at one of it's 2 low voltage terminals, the one with a green at the bASE (i think) while the black one goes to ground through the cdi. cdi must have a good ground too. be sure the connection between the rear coil bracket bolt and the frame is clear of corrosion. unplug he cdi to test the green wire on the plug for continuity to ground.

    a bad cdi can cut out just one cylinder or all sparks.

    do the standard test of ohms between the coil terminals and through the plug wire too, as in the service manual.

    your english is molto bene ! :scooter:
     
    Last edited: Dec 10, 2017
  9. sider

    sider New Member

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    Hello. the English teacher did not think like you !;) tomorrow the text conducting the green wire of the CDI, but all the other tests indicated in the manual I have already made and all falls within the parameters provided by honda in the manual workshop. the sparks are present on all four spark plugs, only I see them rather weak. for this reason I checked the voltage at the output of the CDI. now here it is 2:25 AM and I'm going to sleep, but tomorrow I'll text the green thread and update with the results. Thanks for your suggestions :)
     
  10. squirrelman

    squirrelman Member

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    simply try unplugging the two red connectors to the CDI box and inspect the contacts for corrosion, etc.

    remove , inspect, and clean the connection on the large green ground wire ( with large O in brass) at the right side mid-fairing support bracket bolt.
     
  11. sider

    sider New Member

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    [QUOTE = "squirrelman, post: 577068, member: 3024"] ,........... right side mid-fairing support bracket bolt.[/QUOTE]


    repeating to both: all the connections were opened and cleaned more than once, but there was no oxidation or corrosion. the voltage values on the cables that go to the ignition coils (with only the ignition key turned are regular [equal to the battery voltage values]). the green cable regularly discharges on the bike frame and the cable impedance values are normal. both the pickups and the campulse have an internal impedance (ohms) that fits perfectly with the parameters indicated in the manual, while the coils have an internal impedance of about 3.5 ohms on the primary. secondary perfectly in the range indicated by honda. the suspicions remain on the CDI
     
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