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79 Xs 400 2LO Wont fire

Discussion in 'The Garage' started by barmstrong, Aug 16, 2021.

  1. barmstrong

    barmstrong XS400 Member

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    Bike has been sitting for a lot of years start button and stop switch were missing got the start button repaired put the 2 wires together from the stop switch, got the engine to turn over with the start button, plugs won't fire. What I have done so far : Set the points( not in great shape got new ones ordered) but they were good enough to test fire, fixed them with points file, checked for voltage to coil getting about 9 volts, pulled the condenser off to make sure it is getting a good ground ,didn't really know how to check it, pulled points wire off and it does spark to ground but not very strong. Didnt replace coils can't imagine both going out at the same time Never had so much trouble getting fire from a points system. Any help would be greatly appreciated.
     
  2. barmstrong

    barmstrong XS400 Member

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    Update: Got the new points installed more trouble than the originals had to work on them out of the box to get contact, plus they didn't line up perfectly, still waiting on condenser, cleaned up battery ground, cleaned up grounds on coil ,no help, unhooked wires at points, have 9.6 volts, when I attach wires to points voltage goes away, sounds like insulators are not working so any help would be very appreciated
     
  3. CaptChrome

    CaptChrome XS400 Enthusiast

    One thought - you have done a good job with checking that the grounds are clean, next do a quick check that what is not supposed to be grounded isn't. You may have some wire insulation that broken and making contact with the frame. So, remove the connectors from each end of the wire and check for any continuity to ground and if there is any fix that. It is a long shot, but something else you can verify.
     
  4. xschris

    xschris XS400 Guru Top Contributor

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    Make sure your battery is at 12.5 or more volts. Then the basics like static timing and a new set of plugs. Then a cold compression test. The bike should be between 125 and 155.
     
  5. barmstrong

    barmstrong XS400 Member

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    Thanks very much for all your help! I finally got it to roar, not for very long, I have to put the carbs back on, carb cleaning adventure will be another thread, but its always nice to hear the first sounds of life in 25 years. Took the points all apart to make sure the insulating washers were in place and put on an eBay set of used condensers, couldn't find any new ones, not sure which one did it I suspect it was the points grounding out.
     
  6. CaptChrome

    CaptChrome XS400 Enthusiast

    Great to hear. Regarding the condenser, they are just a capacitor and probably not highly specific to the bike model. If you can find others that fit in the space (new ones for other bikes of the same era), you probably will be in good shape. Old ones do tend to fail over time as the dielectric between the plates of the capacitor dries, leaks, or changes properties.
     
    Buddha likes this.
  7. barmstrong

    barmstrong XS400 Member

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    Thanks for the response. I have been busy got it firing but still won't run , it will roar occasionally with starting fluid but not every time, hooked the carbs back up after cleaning, and new floats, the originals had corrosion holes, tried to solder them and made things worse, and needle seat combo, filled up the bowls nothing happened with that, checked the Time 3 times right on the money at right and left fire, so that's not the issue, supposedly, checked the compression it had 160 in right cylinder and140 in left , not sure how accurate my gauge is, but it should be enough to start. Oh plugs are you guys still running BP7ES or the iridium version, I have denso W22 and thought would check before purchasing. Still maybe coil or condenser related not sure. Im thinking about advancing the time a little closer to top dead center and trying that. Any thoughts!
     
  8. barmstrong

    barmstrong XS400 Member

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    Done some more checking checked time 2 more times, set exactly like book says. Had one coil stop sparking replaced it, was also getting hot. No difference, checked the compression again with throttle open left 145 right 155 . Still waiting on my iridium plugs but don't have much faith that's going to fix anything, the ones I have seem to be sparking good. Im beginning to question my technique for finding the compression stroke. I put my thumb over the hole and turn rotor until I feel pressure then stop, but it is not on the mark, so I turn it slowly until I find the LF or RF mark whichever side im working on and set the points accordingly. I have everything spark, gas and compression makes no sense that it won't run or at least hit on starting fluid . Im using a brand new lawn and garden battery for the testing I assume that would have as much or more power than the small 12 AH battery, but not sure.
     
  9. Buddha

    Buddha XS400 Addict

    You proved you have spark at the plugs, with the plugs out and grounded to case, correct?
    You proved timing is on the mark with timing light, correct?
    You proved the engine is mechanically in shape to run, it has compression within spec.
    How did you prove you have gas at the plugs? Will all the attempts to start with choke then without choke the plugs should be wet (flooded), if they are it's over fueling. If they are bone dry you're not getting gas to the plugs.
    When you try starting fluid and it may or may not fire, is that after a lot of cranking? Plugs could be wet and not firing.
    Just some thoughts, I use this troubleshooting procedure on any gas engine.
     
  10. barmstrong

    barmstrong XS400 Member

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    Thanks for the reply! Haven't had it running long enough to use a timing light but they are statically timed. I had noticed not seeing any gas in the carb throat so thought I would investigate that shortly after I made the last post. I was just trying to get it to run on starting fluid to make sure I had timing right. I looked in carb throat and saw no gas while trying to start it and thought maybe because I didn't have the air filters on there was not enough resistance to properly prime the carbs so I put my hand over the carb throat then gas started coming in then did the other side, has good suction at the carb. I only have the bowls full of gas no tank on it yet, I have the carb adjustment set 2 turns out that is what they were set at before I cleaned them. It acted like it was trying to start and I think I flooded it by putting my hand over the carb throat plus my battery ran down and it was getting dark out. So I will continue tomorrow. Thanks again for taking time to help me I really appreciate it!
     
  11. Buddha

    Buddha XS400 Addict

    You can check timing with timing light by turning ignition on and cranking the engine with the starter, pull the plugs, put them back on the HT wires and ground them to case, that will make cranking easier and faster.
     
    Last edited: Sep 2, 2021
    xschris likes this.
  12. xschris

    xschris XS400 Guru Top Contributor

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    Yes. Test light for static timing and a strobe type timing gun for dynamic timing. My guess the problem is in the timing and points setup.
     
  13. barmstrong

    barmstrong XS400 Member

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    I set the points up with a test light I will try the timing light and see what that tells me, Thanks!
     
  14. barmstrong

    barmstrong XS400 Member

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    Found my timing light haven't used it in many years , you were right, timing not right according to light , that's what i have been thinking the whole time, but I have set it up using a test light numerous times by the book, im at a loss, I don't know whaat I did wrong. So how do you do it with a light move the points a little and check it with light until its right ?
     
  15. Buddha

    Buddha XS400 Addict

    Well how far out are you? You put the timing light pick up on the left coil HT wire, ignition on, crank engine over, what side of LF are you on? If you're on the left side of LF too far advanced, firing on the right side of LF too far retarded.
    The points are gapped correctly, to change the timing for LF you need to rotate the whole points plate with rotation or against rotation depending whether its firing advanced or retarded.
     
  16. Buddha

    Buddha XS400 Addict

    Once you have LF timed by moving the whole points plate, you then need to time RF. To do that you need to move the partial points plate that the right cylinder points are attached to.
     
  17. barmstrong

    barmstrong XS400 Member

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    Trying to figure that out now hard to mash the start button hold the timing light and get down low enough to see the marks then my battery dies again, the battery im using is a brand new Die Hard lawn and garden battery, runs down quickly, starter either pulls a lot of juice or battery is not strong enough, I have the correct one ordered, I thought it might be easier to see in the dark. Thanks for all your help!
     
  18. Buddha

    Buddha XS400 Addict

    No problem, post how you made out! I use a remote starter button, allows freedom of movement:laugh:
     
  19. barmstrong

    barmstrong XS400 Member

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    Just finished checking, the left fire was right on the mark with the timing light, couldn't get the inductive pickup to work on right side so I pulled the plug to check and it is firing, so I timed it again with the test light, it was off again, so I reset it with test light . These new points are cheaply made this particular set that I keep having to reset didn't make good flat contact right out of the box ,and they aren't cheap like they used to be, if I hadn't already purchsed them I might go for the electronic ignition kit, and I still might! Oh! Going to try to crank it a little later battery dead again, evidently the Advanced Auto Die Hards are not like the original Sears ones, or im charging on the wrong setting ,on my charger I have motorcycle icon and a car icon I choose the motorcycle one, im assuming its twelve volts. Thanks for your quick response!
     
  20. Buddha

    Buddha XS400 Addict

    LOL, never assume. Use a voltmeter and see what voltage your charger is putting out on the motorcycle charge mode.
     

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