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1978 XS400E

Discussion in 'The Garage' started by Quinton Carnahan, Jul 31, 2020.

  1. Quinton Carnahan

    Quinton Carnahan XS400 New Member

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    Idaho
    I recently picked up a 78 xs400 barn find For 300$. It has 250 original Miles on it but its been sitting since 1991, overall the bike is in fantastic shape, a mouse chewed on the seat a little. Little rust on the pipes and the tires are toast... the previous owner drained all the gas even the inside of the tank is clean. With all that being said..

    I ran a kickstart compression test and got 60psi on the right and the left didnt budge at all.. im sure i could part it out and come out ahead but i really like the bike. Its my first yamaha and dont know alot about it. Any tips would be appreciated i plan on starting the tear down tomorrow.
     

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  2. motoTrooper

    motoTrooper XS400 Addict

    Before you change the oil, maybe pour some ATF or Marvel Mystery oil into the cylinders and let it soak overnight to loosen the piston rings and check and adjust the valves accordingly. To get an accurate compression reading the throttle needs to be held wide open also.
     
  3. amc49

    amc49 XS400 Enthusiast

    You must absolutely get the compression numbers up if you hope to run it. 100 and less don't bother trying.

    Use no more than a tablespoon of whatever you put in plug holes or you risk hydrolocking the engine and engine damage, have both plugs removed while testing too.
     
  4. Quinton Carnahan

    Quinton Carnahan XS400 New Member

    2
    0
    1
    Idaho
    I put some marvel mystery oil in it and its sitting now, i have found gaskets online but it seems like parts for this engine seem to be pretty scarce so im hoping thats all it is
     
  5. xschris

    xschris a lifestyle not a trend Top Contributor

    In order for the bike to run proper you need at least 120 psi of compression. These have 155+ when they are new. The bike is a 2-E model. The E has a lot of different parts on it. This will help when looking for correct fitting parts.
     

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