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Brought home a XS cafe... need hel getting to fire

Discussion in 'The Garage' started by Jay, Apr 20, 2020.

  1. Jay

    Jay XS400 Enthusiast

    HI all, this bike is my first venture to Yamaha, so I am new on this forum. I have been going through a ton of threads, doing my research, etc.

    A bit about me... I am not new to motorcycles, or building them, fixing them, crashing them, etc. I am an ex CCS AM road racer, previously running a Ducati and Kawi. Having gotten rid of all of the race track goodies, I wanted a simple cafe bike for the street, so my girl and I can ride. I found a '77 XS400 cafe, and bought it.

    The bike sat unfinished, and I knew I would have some bugs to go through. But I am beginning to suspect I am going down a rabbit hole. Looking to you guys for some help.

    Problem:
    Bike will not fire. Either via kick, or starter

    General info:
    • Cylinders have 160-170 psi compression. I have run the comp test several times... kicking it, on the starter, adding a bit of oil to the cylinders, results consistently come back at 160-170PSI.
    • I have fully rewired bike. It was pretty ratty when I got it. Bike has aftermarket harness, with minimal electrics. Everything operates as it should.
    • I have 12v at coils with ignition on
    • I have spark at plugs
    • Carbs have been cleaned, and I have fuel
    • Plugs are not fouled
    So, since I know I have the 3 big items... spark, fuel, and compression, I suspect perhaps timing is out, or maybe valves are too tight. So I start going over the valves, and notice almost immediately that on the left cylinder, my compression stroke seems to be 180* out. Perhaps I am wrong, but as the the crank spins, and it comes up on LT, this should be TDC for the left cylinder. But I am getting compression nowhere near this mark. Ive referenced the Haynes manual, and there is not a ton of detail on this. As there really shouldnt be... its simple enough.

    Is it possible on these to have the crank / cam phasing be 180* out?
     
  2. Have you checked to see if the coils are wired wrong? They could be wired backwards. I am doing a custom harness from a photo I found elsewhere on the forum and will post.

    make sure all of your coils are grounded properly as well.
     

    Attached Files:

  3. Jay

    Jay XS400 Enthusiast

    backwards, as in left to right? No im not sure they are correct, but what i do know is the coil subharness (for lack of better description) is OEM, and I think it would be tough to get it backwards. Again, not 100% sure though.

    I will check this
     
  4. I was thinking left to right. There are many reasons you could have spark and not firing.

    I wired a custom harness and found its pretty easy to mess up on coils left to right. If that part of the harness is factory and the part wired to the Cdi box if factory that that won’t be the issue. Timing, or lack of fuel or proper air fuel mixture. Is there still a kill switch on the bike?
     
  5. Jay

    Jay XS400 Enthusiast

    Yes, there is a kill switch on the bike.
    The 12V switched lead that powers the coils is a separate circuit from the kill switch.

    I need to go about checking the coils for sure. My bigger concern is that by what I am experiencing, when my left cylinder comes up on compression, I am nowhere near the LF (or even LT) markings, and I am curious is the cam is phased 180* out from the crank
     
  6. Jay

    Jay XS400 Enthusiast

    Hey guys, how do we post pics? I would love a second set of eyes to confirm that the cam is phased t the crank correctly. Going by the service manual I believe it is
     
  7. Ben_Wagner

    Ben_Wagner XS400 Member

    Down below where it says "Post Reply" there should be a button that says "Upload an Image or File". After the file is uploaded you can click "Thumbnail" or "Full Image" to insert the picture where your cursor is.
     
    Jay likes this.
  8. Gra900

    Gra900 XS400 Enthusiast

    Hi Jay, just a quick couple of thoughts, apologies if I’m teaching grandmothers to suck eggs as you clearly have lots of knowledge already . LT will come up on the exhaust stroke as well as firing stroke, no compression then, any signs that the motors been rebuilt by a PO, they could get camshaft 180 out, and you know these bikes are 180 cranks.
    Othe possibilities- do you have points or TCI? Possible that something has been assembled wrong in the past there too if points.
    Good luck
     
    Jay likes this.
  9. Jay

    Jay XS400 Enthusiast

    Ben,
    Thank you. Ive been fighting with my photobucket to upload pics and embed from, cant get it to work, ill go the route you suggested.

    Gra - I agree. Bike being brand new to me, and not knowing much of its history, I think I have been willing to dig a bit deeper and confirm things are up to snuff. The bike has points in it, and I have confirmed that the coils are hooked up backwards. Assuming, that when looking at the points, the left side is the left cylinder (orange lead from this breaker to the coil), and the right side breaker is for the right cylinder (white lead from breaker to coil)

    Below are a couple pics, confirming cam is in correctly, according to service manual bring the motor up on TDC cyl 1, and install the cam so that the ID marks on the cam gear are horizontal in relation to the head. The marks are tough to see in the cam pic, but in person they sit horizontal

    IMG_5583.jpg IMG_5586.jpg
     
  10. Jay

    Jay XS400 Enthusiast

    Also, Confirming coils are wired incorrect, as I am 99.9% sure they are:

    IMG_5588.jpg
    IMG_5589.jpg
     
  11. Jay

    Jay XS400 Enthusiast

    A few pics of the bike as well

    60790801561__269332AF-95DF-4CE6-A309-BD98B695DAF0.JPG 60824725746__5AF5D463-BFF7-4E99-B1CA-07ACB8DB9404.JPG 60840855945__60E3B067-1404-47E4-BC53-6D4A12C7A7C7.jpg
     
  12. xschris

    xschris a lifestyle not a trend Top Contributor

    Cam is off 180 The pin at the end and the "pip" on the sprocket should be set at the LT mark.
    DSC03808.JPG DSC03809.JPG
     
  13. Jay

    Jay XS400 Enthusiast

    Chris is it possible I am on the wrong stroke?
     
  14. xschris

    xschris a lifestyle not a trend Top Contributor

    I would set the cam to it's correct position. This is in the haynes manual pg. 50-53 This will help with setting timing and valves also.
     
  15. Jay

    Jay XS400 Enthusiast

    Looking at your pic, the pip lines up with the oiling holes on the cam journals. On the pic I posted, I dont have both oiling holes on top, I only have 1.

    Here is a better pic:
    IMG_5605.jpg

    I spun the motor until it comes back up on LT, and the left cylinder is back up at top. How does this look to you?
    IMG_5606.jpg IMG_5607.jpg
     
  16. xschris

    xschris a lifestyle not a trend Top Contributor

    That's how it should be.
     
    Jay likes this.
  17. xschris

    xschris a lifestyle not a trend Top Contributor

    I have noticed that the bike has xs360 carbs on it. Make sure your using parts and setting for those type of carbs. The xs400 uses a very different style. Also pods like yours are a bad setup for the type carbs. If you must use pods, dark foam uni's work better. Also using the stock H-pipe setup helps. As always the stock boxes and filters are best for overall performance.
     
  18. Jay

    Jay XS400 Enthusiast

    Chris, you are a wealth of information. Thank you.

    Once I have it running I will be putting it on a dyno to watch how it is fueling, and set the carbs up from there. Thank you for the heads up on the type of carbs.
    I will absolutey only be using Mikuni stuff when I get to that point.

    I had my suspicions about the filters. I will be looking for the uni's
     
  19. xschris

    xschris a lifestyle not a trend Top Contributor

    Make sure you have the xs360 carb boot cages. The 360 carbs are a lot heavier than the xs400 ones. I use the cages on all my xs400 bikes as it adds extra support. Also it's a good idea to use the stock H-pipe and crank case vent hose for tuning and it also help hold them up.
    DSC03359.JPG DSC03810.JPG
     
  20. Jay

    Jay XS400 Enthusiast

    I definitely do not have the cages. And the pinch bolts on the boot clamps are different side to side.. phillips on 1, and flathead on the other. The cage just slips over the rubber intake manifold?
     

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