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1975 xs650b fuel/air mix screw setting?

Discussion in 'The Garage' started by Buckminster, Jun 22, 2013.

  1. 5twins

    5twins XS650 Guru Top Contributor

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    You'll have to remove the caps or caps and plugs wires as an "assembly" to measure through them. Stock plug wires should be plain copper core non-resistor wires so measuring through them along with the cap shouldn't affect the reading. The stock plug caps have a rather odd rating of something like 8K or 9K ohms. What happens when they start going bad is that resistance starts climbing. Eventually it gets so high it starts choking off the spark. Higher RPM operation can sometimes push through this higher resistance but lower RPM operation may not. This could be your problem.

    If you haven't done so, it's probably a good idea to make all new, fresh connections between the plug wires, caps, and coils. Trim about 1/4" off both ends of your plug wires to get to some fresh wire. Then strip about another 1/8" of the insulation off and fan the wire strands out in a radial pattern like so .....

    [​IMG]

    This will insure good contact and a good connection between the wire and cap or coil. If you look inside the end of the plug cap that goes on the wire, you will see what looks like the pointy end of a wood screw. Basically, you "screw" the cap onto the wire. At the coil, you may find the same wood screw looking thing but many times it's just a pointed metal pin, like the end of a nail. With that, you just push the wire onto it.
     
  2. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    I understand what you’re saying about how to make new connections but before I do that how can I measure the ohms right now is what I’m asking?
    Can I just stick one of the leads inside the spark plug cap? LOL I have no idea
     
  3. 5twins

    5twins XS650 Guru Top Contributor

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    No, the cap has to be off so you can measure through it. It's easy, it just "screws" off and then back on. You need to stick one meter probe in where the spark plug goes and the other in the other end where the wire goes in.
     
  4. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    I actually just did what you recommended. I cut a quarter inch off totally and another eighth of insulation and found out the wiring. So you’re saying stick one of the probes right inside this cap center where the screw screws in? If so which one negative or positive probe? Also what do I put the voltmeter on?
     

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  5. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    also see picture.....is this affecting anything? When the bike is running and I push up on it the bike suddenly dies. I know this is not a true choke so is it necessary to just leave it where it’s at or should I put the lever on it because there is none??
     

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  6. 5twins

    5twins XS650 Guru Top Contributor

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    Set your meter on the ohms scale. It doesn't matter which probe goes in which end of the plug cap, you're just measuring resistance through it so reading should be the same in either direction.

    Without a choke lever on there, you can't turn the choke on. Usually you need the choke for cold starts on these. When you lift that little lever in your pic, you're turning the choke on. If the bike is warmed up then yes, that will usually stall it. The way the lever is resting before you likted it is the choke off position so it shouldn't be causing your stalling.
     
    75XSFLORIDA likes this.
  7. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    OK just so to make sure I’m understanding this. One probe goes in the end of the endcap and the other probe actually goes into the cylinder hole where the spark plug goes into after I take the spark plug out, just touching the threads or something?
    Also turn the ignition on correct? But not starting the bike
     
  8. 5twins

    5twins XS650 Guru Top Contributor

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    No, you're lost, lol. Take the plug cap and your meter and walk away from the bike. The bike isn't involved in this test at all. This is an independent test of a component removed from the bike. You don't touch the bike or turn it on, or anything like that.
     
  9. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    So pull the plug cap off the spark plug wire and stick one probe in that specific cap where the tip of the plug goes....ok i get that.
    Where does the other probe go then?? Touch it to the other side of that cap, on the point on the end of that screw?? LOL That’s why I’m lost
     

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