Misfire, 1985 VMax 20,800 miles

Discussion in 'General VMax Questions' started by Primaris, Oct 5, 2019.

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  1. Oct 5, 2019 #1

    Primaris

    Primaris

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    I have a new to me 1985 that was running great. Last night it developed a misfire.

    What has me scratching my head is when pulling the spark plug bootss on the right side of the motor nothing changes. Now unless the Vmax is a diesel and I don't know it, I don't think the misfire is bad enough for two cylinders to be dead. Plus the exhaust do warm up. WTH is going on? What can cause both of the right cylinders to misfire?

    Thanks!
     
  2. Oct 6, 2019 #2

    one2dmax

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    Could be CDI box going south
     
  3. Oct 7, 2019 #3

    Primaris

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    Thanks for the input.

    I checked the Haynes manual and I didn't see a CDI box listed. Is the CDI box the same thing as the Ignition Control Unit?
     
  4. Oct 7, 2019 #4

    Fire-medic

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    Yes, behind the steering head.
     
  5. Oct 7, 2019 #5

    Primaris

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    FYI the misfire seemed to be getting worse. On the ride I felt what seemed like the low fuel warning. But, then the misfire became apparent. So it sort of grew in severity.

    What is going to be the best way to diagnose and fix this issue?
    Thanks.
     
  6. Oct 7, 2019 #6

    Pighuntingpuppy

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    Lets start simple. Lets verify the misfire first. If you have a spark plug that you arent using, that would be a great start to determine who has lost spark. What you will want to do is pull one spark plug boot at a time and see if you have spark reaching the spark plug. You will need to make a ground from the spark plug to the chassis to complete the circuit. If you find you have a cylinder missing spark, it could be a wire or boot, maybe a coil. If 2 are missing spark, that could be a pickup coil going out. I believe that your era Max has 2 pickup coils. I am not quite sure if one is a master and the other a slave or if one operates 1 bank of coils and the other operates the others.

    Before we worry about what BBQ sauce to put on the pig, we must first kill the pig.
     
  7. Oct 8, 2019 #7

    MaxMidnight

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    Given that it seems to be affecting the two RH cylinders then my initial thought would be to rule out caps/ leads and coils for the time being.

    Pursuing the pick-up coil theory seems reasonable; can someone confirm which coil sparks which pair of cylinders?

    Whilst an old plug will help check for a spark it would be worthwhile investing in something like this which will be a better method of checking the ignition system.
     
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  8. Oct 8, 2019 #8

    Primaris

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    Checked. It has spark to the two right hand cylinders.
    I looked in the tank with a mirror and the back portion of the tank is pretty rusty :(
     
  9. Oct 9, 2019 #9

    Fire-medic

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    There are all-sorts of ways to clean a tank. Phosphoric acid, cleaning vinegar (higher % acid than food-grade), electrolysis, muriatic acid, steel shot and mineral spirits agitated, and more.
     
  10. Oct 13, 2019 #10

    Primaris

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    The bike has now become very hard to start. The tach seems to stop working at below 2k rpm. It seems to be draining the battery instead of charging it when running.
     
  11. Oct 13, 2019 #11

    sdt354

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    If the exhaust warm up, the cylinders are firing. Common issue on early gen 1's is the charging system not performing well enough to run properly. 13.5 volts is a minimum, depending on battery voltage. The regulators on the early models weren't very good. But a check of the total charging system, including the battery should be performed. All you need to know is in the archives here.Stators don't last forever either. Heat does them in eventually.
     
    Last edited: Oct 20, 2019 at 9:57 AM
  12. Oct 15, 2019 #12

    Primaris

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    So where do I get replacement; Stator, and Rectifier/Regulator?
     
  13. Oct 16, 2019 #13

    MaxMidnight

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    You don't...until you have checked the systen an identified where the issue lies.
    Have a look here
     
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  14. Oct 16, 2019 #14

    sdt354

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    If y
    If you do need them, there are lots of options. Later gen 1 regulators, mosfet regulators, Venture Stators, higher output units, all available. Testing first is prudent as MaxMidnight mentioned. No need to toss $$ at something that works already. Start with a voltmeter.
     
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  15. Oct 16, 2019 #15

    Primaris

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    The bike is now at a mechanics shop. Once the misfire became intermittent it is no longer within my scope to fix. And, I just want to get back to riding since the weather here is finally getting a bit cooler.

    Why not replace the 34 year old parts now? How much longer can they possibly last?

    I would like to keep the bike as stock as it is now.
    Are stock parts available and if so where?
    Or, are stock replacement parts junk?
    Are the later Gen1 regulators a direct swap?

    I read a bunch of the stickied threads in the forum, but I didn't see any working links to where to buy direct replacement parts.
     
  16. Oct 16, 2019 #16

    Traumahawk

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    Yes....its always a good thing to have newer parts... because everything will fail eventually. I think the point that maxmidnight was bringing up....was to figure out what the problem is before you just use a shotgun approach and just throw money at the problem. Most people dont have the extra funds available to have parts on hand that they might not necessarily need.
     
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  17. Oct 16, 2019 #17

    Traumahawk

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    Sean Morley is one of the best places to buy replacement parts. He has been a Vmax supporter and is on this page. His name on this forum is one2dmax. The best way to get him is email. One2dmax@aol.com

    Sean really is the man on a lot of stuff....especially if you are modifying stuff. Where I go for strictly stock parts is partzilla. I know some people on this forum will go to Ron Ayers. It comes down to which one is cheaper and personal preference.
     
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  18. Oct 17, 2019 at 4:26 AM #18

    MaxMidnight

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    Music to a repair shops ears!

    How do you decide which of the thirty four year old parts to replace and, IMO more importantly, what if that doesn't fix the issue?

    Do you mean original equipment (OE) or aftermarket?
    OE from a Yameringha dealer or aftermarket do a search on the internet for the part you are looking for.
    OE is good kit, aftermarket you tend to get what you pay for.

    They use the same mounting point and as far as I'm aware (but stand to be corrected) the are the same intenally. The later R/R's have an earth lead; the earlier ones relied on the eath via the mounting point.
    You would get the same effect by adding an earth lead to the earlier version.

    You can replace parts and in the case of electrical items fix the fault...not because the component was faulty but because the act of making and breaking the connection has cleaned it up thus giving good electrical contact.

    By all means go your own way but if you do the proper diagnosis not only do you stand a much better chance of getting a first time fix but also won't waste money needlessly.
     
  19. Oct 17, 2019 at 8:27 AM #19

    Primaris

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    @MaxMidnight The bike is at a shop. I can pay time to diagnose then replace. Or, I can pay to replace. Right? I just want to get back riding. I appreciate the help.

    Hell I'm not sure the electrical issues are even related to the misfire. There could be a carb issue or a ICU issue still.

    Correct me if I'm wrong. The stator is not available: https://www.partzilla.com/catalog/yamaha/motorcycle/1985/v-max-1200-vmx12n/generator

    This is the right regulator: https://www.partzilla.com/catalog/yamaha/motorcycle/1985/v-max-1200-vmx12n/electrical-2
     
  20. Oct 18, 2019 at 7:40 AM #20

    sdt354

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    I'm sure Sean can sell you any part needed. Just make sure the shop takes the ten minutes to test the charging system. It's a a lot quicker than removing the carb rack. After the issue is identified and fixed, upgrades are a good idea.
     

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