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XS250 Special 1983

Discussion in 'Yamaha 250cc Twins' started by tristan, Apr 29, 2016.

  1. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    Looking good Tristan.

    Other than what Murdo suggested...

    The standard airbox on the XS400R was side fed and the filter position seemed to suggest that the carbs got slightly different access to the incoming air. The XS400R ran different sized main jets. My guess is that one cylinder got a tiny bit more air than the other and the men in white coats balanced the system by running one cylinder a little richer that the other. I'm not sure if this is the same for the XS250 airbox, but it might be. So, if you've gone to pod filters you may find that the cylinder with the smaller main jet will run a little hotter than the other. Just a guess on my part.

    Cheers

    Frank
     
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    Last edited: Sep 15, 2016
  2. tristan

    tristan XS250 Nomad

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    Thanks Murdo I tuned the RHS cylinder as rich as possible and the temp was still double LHS... so I am going to get the carbies out again and swap the main jets over, I did this before but may have made an error doing so, it seems the jets are commonly different sizes on these YICS motors from factory. Ill check to see they're clean and balanced etc.

    If that doesn't work then I will have to operate and as you suggest timing might be first.

    I am using the 82 XS400 DOHC manual as the specs are all identical accept for critical 250cc settings which I just can't find, problem is the Haynes manual up to 1984 models is for SOHC only and I have a DOHC... still looking. Might be easier to buy a 400cc motor?

    cheers
    Trist
     
  3. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    Tristan, I have some 400 DOHC and SOHC information in PDF if it helps. Have you checked your valve clearances?
     

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