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78 XS650 Coils

Discussion in 'The Garage' started by IMAN, Feb 3, 2012.

  1. IMAN

    IMAN XS650 Member

    Hello fellow xs650 members,

    This will be my first post and sure of many more as I just dove into a 78 XS650 about 1 month ago. I enjoy reading all of the info on this site related to the XS650, but like any new xs650 new owner I have problems and to stubborn to ask for help..lol...Sure the PO said everything was great and it ran!(BS) I have stalked the site about 3 weeks trying to learn and read all the info I can find on the bike(at least 15hr a week), but I'm a bit unsure about where to go next. Well let me give you a brief description of what I have done and what is going on.

    1.) Got bike home and checked
    Cleaned(changed) oil, slump,and tank(rust)
    Fuses 20A(Great beep w/ M-Meter)

    Replaced spark plugs(no spark to begin with and still no spark)

    So my question is how to properly test a 78XS650 coil(s)PLACE mm ON WHAT SETTING and WHERE TO PLACE mm ON COIL OR POWER-SOURCE FROM bat), b/c that's the next step of checking for spark(correct)? From what I have read I place the MM..+ on R/W(from Bat) and MM..G on orange from battery no Volts( only volts I have are 12.9 at battery!)( If I place MM on coils where they are solder next to plastic or hard metal I get 4.2 on MM_)Thought I gained knowledge about it though a great search of info from goggle but from readings I find aren't enough for me!

    That's all the info I can think of at this moment but if anything comes up I can explain, THE PROBLEM............!!!!!!!!!!!!l. THX IN ADVANCE FOR THE HELP!

    Info I have is CLYMER- Service,Repair, Maintenance(book).....So not much b/c its does not go into detail!
  2. 5twins

    5twins XS650 Guru

    Take a look at the factory shop manual which is online here .....


    It contains coil testing info.
  3. IMAN

    IMAN XS650 Member

    Thank you for the quick reply!, but whats section does it seem to be under

    1978 XS650SE Parts Manual?
    Engine or Chassis can't see, to find it!
  4. 5twins

    5twins XS650 Guru

    XS650 Service Manual 1978-1981, 650E Electrical.
  5. IMAN

    IMAN XS650 Member

    If you can point me in the right direction of testing coils on a points system that would be great. Only thing I need to understand is where to look and hook for the leads and negative from what point to another from the M -meter

    MM have red and black so do I hook red to red wire on the xs650 wire harness or the coil itself. and Black to orange?........would be alot easier to just call me.

    Please just PM with yr number!
  6. Do you have a Standard or a Special i.e. do you have 4 fuses or just 1 fuse?
  7. IMAN

    IMAN XS650 Member


    It's going to be 4 fuses, special... All 4 checked out with MM and gave me a beep!
  8. IMAN

    IMAN XS650 Member

    This is the MM I'm using and what setting would be used for the coil test
  9. jchrisk1

    jchrisk1 XS650 Junkie

  10. IMAN

    IMAN XS650 Member

    OK I have found the answers I need I believe, but want to run it by before I test.

    My coils have Brown and Orange so my R/W will be Brown correct?

    Batery power is disconnected from main harness to coils?
    To test prmary is MM+ to R/W(Brown) and MM-to Orange? Should read 3.9 ohms
    To test secoundary is MM+ to plug wire end(cap removed) and MM- to orange? Should read 8K ohms

    One last question before I test what should be the Voltage at end of the main wireing harness that connects to the coils coming from battery? 12V

    Thanks in advance for all the info!
  11. 5twins

    5twins XS650 Guru

    Yes, yes, and maybe. Test the voltage at the battery first. You should get very close to that at the coil power wires. You may see a couple tenths of a volt drop because of all the connections and switches between the battery and coils. If you get much less than that, say a volt or 2, then you need to clean all the connections and switches. Low power to the coils is a common problem on old bikes. It can really hurt performance or even make the bike not run at all.
  12. IMAN

    IMAN XS650 Member

    Alright just tested coils for voltage so here are the results.

    Primary(200 setting on MM)
    Left coil is 3.8 ohms
    Right coil is 3.8ohms

    Secondary(20k setting on MM)
    Left coil 8.3 ohms
    Right coil 8.3 ohms

    So coils should be fine?

    Checked voltage going from battery, to coils and plug wires. With MM- grounded to battery and MM+ on R/W wire(s) from harness, bike turned on, and kill switch set to RUN I get the reading of 11.8 volts going to both coils and also to each plug wire(s). So with finding this information out I should be good on getting power to coils and plug wires? If anyone sees and mistakes I'm doing when testing voltage, please let me know b/c I'm new to working on electric! Heres the break down

    Volts to coils 11.8
    Volts to plug wires 11.8
    Volts to plug caps 11.6

    If everything checks out correct I should now look to the points to get spark correct?
  13. XSLeo

    XSLeo XS650 Guru

    How does the battery voltage compare to the red/white wire at the coils voltage?
    As 5twins mentioned a large difference can effect if and how the bike runs.
    With 11.8 at the coils and 13.5 at the battery is a bit much voltage drop. With 13.5 volts at the battery 13 volts at the coils is about right.
    11.8 a 12.5 battery sounds ok.
    Personally I don't like more than about .3 volts lost between the battery and coil.
    Most of this loss is in the key switch or engine stop switch. Sometimes in the fuses or wiring connections. Most of these things can be opened up and cleaned, bright and shiny is a good thing. A small dab of dialectric grease will help keep connections well connected.
    And yes, at this point the points will be suspect. They need clean contact surfaces and be properly gapped and timed.
    Set the can chain tension first, then set the valves, then do the points. This order is neasry because the cam chain tension effects the cam timing as will as the points timing. Done in any other order gets mixed up setting.
    It's all in the repair manual. Just set and gap the upper set first, then the lower.
  14. IMAN

    IMAN XS650 Member

    Well Battery is around 12.6 and as you saw volts at coil is about 11.8.
    O..boy the points, thing I have been trying not to miss with. Time to sit and read!
  15. XSLeo

    XSLeo XS650 Guru

    Those voltage numbers should get it running. The point aren't that bad, it just takes prctice to do them quickly. Just take your time and be clean. Any contaminents on the points will cause you greif. Get some spray electrical contact cleaner and som white paper, like business cards are made from. After you gap and time the points, spray the white card with the contact cleaner and pull the dampened carb through closed points, this cleans off any crud from the adjusting.
  16. If your bike still has the original 4 position fuse panel, I highly recommend you replace it with automotive blade type fuses. The panel may look OK but the clips loose tension and resistance increases. Don't even try to test the fuse panel, just replace it and solder/ heat shrink the splices.
  17. IMAN

    IMAN XS650 Member

    Thanks for the information on the points and fuses guys. I will be tackling this through out the week, so I'll keep you posted on the progress. Thanks again much help!
  18. IMAN

    IMAN XS650 Member

    Well as I said I would keep you guys posted. The points were the problem as I suspected.
    I took the information from here on how to go about and cleaning them with a bit of sand paper and lacquer thinner. Soon as I did that I have spark at the points and plugs. The spark at the points is a bit tanish, but the spark at the plugs is more of a white instead of a blue. I tried to crank it over to see if it would start, but no luck. I sprayed a dash of starter fluid in both carbs and got a loud pop, guessing the spark caught the fumes. I did not drain the float bowl of gas before I tried to crank her. So tell me if Im wrong, but draining the float bowl is next in the process to get clean gas in the carbs to see if she will crank. If no start then I should go with the timing of setting the can chain tension first, then set the valves, then do the points. Thx guys!
  19. XSLeo

    XSLeo XS650 Guru

    Doing A tune up involves doing things in order, this order is
    Set cam chain tension
    Set valve clearance
    Set points gap
    Set points timing
    At this point you should have spark at the right time.
    The color of arcing at the points is meaningless. Very noticable arcing can mean a bad condenser. If the condenser is good it keeps the arcing at the points to a minimum.
    Good spark is a nice fat blue spark.
    The voltage going to the coil should be very close to battery voltage. I like less than about .3 volts. As in 12.5 volts at the battery with no less than 12.2 at the coils.
    The stock coils put out around 10,000 volts at 4000 rpms with 14.5 volts at the coil.
    With 12.5 volts at the coil this drops to around 8000 volts. If the voltage at the points is much lower the coil output drops even farther, to less than 7000 volts. As I recall it takes about 6000 volts to fire the plugs.
    So be sure you are getting battery voltage at the coils.
    Last edited: Feb 8, 2012
  20. IMAN

    IMAN XS650 Member

    Thanks for the correct process of timing Leo! This morning I drain the old smelling gas from the float bowl, then turned on the petcocks to make sure I was getting fresh gas to the carbs(success) both carbs are getting fresh gas. Turned her over still just a loud pop, then a low pop-pop-pop. Friday I will be going over all connection cleaning them as well as the timing to make sure I'm getting spark at the correct time. PO said he road it last in DEC, but I know how you can take that will a grain of salt!


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