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78 xs 400 E rebuild and modify

Discussion in 'The Garage' started by Tyler Shiells, Mar 30, 2017.

  1. tmp_533-20170329_111415-696497489.jpg tmp_533-20170330_114315-1513730946.jpg tmp_533-20170330_1143391917843196.jpg tmp_533-20170330_114400866068612.jpg tmp_533-20170330_114434-1383367211.jpg
    Hi I'm Tyler.

    I bought a 78 xs 400 for $150 that looks like it's been sitting outside for a decade.
    I plan to bring this bike back to life, with modifications. I've been reading everything I can about this bike on the forum and have already established the bike can create a spark. Only with the kicker tho, not the starter.
    I can get the starter to crank if I hook 12v directly to it but no spark at the plug . Not sure why? I'm not sure if the solenoid works. I do get an ohm reading through the large nuts if I have power hooked up. The starter button is gone and when I push it in with a screwdriver I do get a small click but no crank in the starter.

    I don't have any air boxes so I'm thinking of going with pods. I am familiar with rejetting but still may need some help.
    I'm going to do an oil change and carb clean this wknd and see if anything sputters to life if i kickstart it. Is it alright to do that with no air box if I just cover the H-pipe with some filter material?
    Anyway there's a lot of work to be done. Breaks need full rebuilds. Wheels spin good so bearing are prbly ok. Not sure about the suspension yet.
  2. xschris

    xschris a lifestyle not a trend Top Contributor

    Welcome to the forum. I would pull everything apart and clean and grease it all. New rubber chain and sprockets. Adjust and clean every part. I would put uni filters on the stock H-pipe if you don't have the stock boxes. With a bike this neglected there can be a lot of safety issues. If you have never heard the motor run I would do a dry and wet compression test. If that is good then start on the other stuff.
  3. Thanks for the tips. Should I spend the money on an oil change before I do the compression test? Also not sure the difference between wet and dry test?
  4. Will I be able to do the compression test without the carbs on the bike?
  5. xschris

    xschris a lifestyle not a trend Top Contributor

    Yes you can test without carbs on the bike. How long did the bike sit? How many miles on it? Did it sit outside? If the oil has been in there for years I would drain it all out, empty the sump and replace the filter (soak it in oil before putting back in). If the motor has sat for a while I would pull the plugs and spray oil in them as well as the intake and the exhaust ports. This will lube everything well before you start turning it over. A wet test is when you put oil in the cylinders before a test. Dry is without. If compression goes up with wet the piston rings a worn. If the numbers are low even with a wet test it's the valves. Good is 135+ great is 150+ The bike still may run at 120 but it's not going to do it well.
    Spiffarino likes this.
  6. Right on xschris. Sounds simple enough.

    The bike has 35,000 kms on it.

    I am not certain weather it sat for long or not but long enough that the brake calipers are seized and the master cylinders, front and back are decaying.
    Also on the intake boots, one barb as a rubber cap, the other nothing. Is there a vent hose or something ment to attach there?

  7. dgoodsy

    dgoodsy XS400 Enthusiast

    The uncapped barb is supposed to have a line run from it to the vacuum petcock. The vacuum petcocks often get replaced with manual petcocks, your bike may or may not have one. If you do not have a vacuum petcock that barb needs to be capped off or it turns into a massive vacuum leak.
  8. I just checked the petcock and the line is attached there. Thanks
  9. Does anyone have an idea why I get a spark with the kicker but not the starter? The starter cranks over but no spark. I am bypasses the starter solenoid to test the starter.
  10. xschris

    xschris a lifestyle not a trend Top Contributor

    Starter could be draining too much power maybe. Jumping the starter without putting power to the rest of the bike will not give you a spark. With the condition of the bike it could be anything, wiring, ignition.... Did you get a compression test?
  11. I thought I'd check the valves first, they were a little tight and loose. So I adjusted to the proper specs.

    I will check the compression this wknd. I won't have a new oil filter in time, as it has to be ordered. Hopefully that won't effect the compression test?
  12. xschris

    xschris a lifestyle not a trend Top Contributor

    It should not ,but you don't want contaminated and dirty oil moving around the motor while you turn it over. If the old filter is packed full of junk your bike may have poor oil pressure. How did your sump screen look when you opened it up?
  13. I haven't opened it up or drained the oil yet. But from looking at the dip stick the oil is quite black. I'll find out Sunday, what condition it is in.
  14. THe local auto store actually had a Fram oil filter for a 78 xs, kinda surprised. So I'll be able to change both oil and filter and hopefully get some good compression on both cylinders.
  15. xschris

    xschris a lifestyle not a trend Top Contributor

    Don't forget the sump screen. A lot of nasty stuff ends up down there.
  16. The screen looks OK to me. The oil was a little thick on the cover plate.

    Attached Files:

  17. compression test results

    Right cylinder Dry 135 wet 165
    Left cylinder Dry 40 wet 100

    Looks like some rebuilding is in order?
  18. xschris

    xschris a lifestyle not a trend Top Contributor

    That left one is done.
  19. You got that right Chris.
    I pulled the engine. 20170402_161942.jpg

    And pulled the cylinder head off.

    The left cylinders is packed full of sludge

    How do the valves look?
    20170402_174928.jpg 20170402_174940.jpg

    An here is the piston rings up close

    So I'll be ordering all new gaskets. Piston rings. How about the piston themselves, still good?
    And do you think I'll need new valves?

    Attached Files:

  20. xschris

    xschris a lifestyle not a trend Top Contributor

    I would replace all seals and gaskets. Make sure the valves and guides are in spec. Do at least a valve lap. If your pistons are in spec rings and a hone may be all you need. Spec all parts you can and replace as needed.

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