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Does this sound right to you?

Discussion in 'The Garage' started by TheOfficialRJ, Mar 30, 2021.

  1. TheOfficialRJ

    TheOfficialRJ XS400 New Member

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    Hello everyone, I wanted to get your opinion on whether this bike is running on both cylinders or not. I've had a problem with this bike before where it was only firing on 1 cylinder. I know this because one side was blowing cold air out of the exhaust. The head was cold as well on that same side.

    The bike was at the shop recently and it was making close to 30HP at the dyno. I doubt it would do that on 1 cylinder. The carbs have been rebuilt and it does have spark on both sides. I will test the ignition coils next if it doesn't sound right to you guys.
     
    Last edited: Mar 30, 2021
  2. xschris

    xschris XS400 Guru Top Contributor

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    Hard to tell from the vid but sound like you might have pods and some sort of open exhaust of some kind. The bike stock should get close to 40hp in stock form and definitely the early 77-79 bikes. The factory says 38hp and bike mag test from back then I think where 37 with 24lbs of torque. That's for a stock bike. Have you done a compression test?
     
  3. amc49

    amc49 XS400 Junkie

    Running on both cylinders but not well. Sounds low on power.
     
  4. TheOfficialRJ

    TheOfficialRJ XS400 New Member

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    Thanks for your reply, Chris! My intake setup is completely stock. The exhaust pipes are aftermarket.
    The shop did a compression test and confirmed it has compression. I rode the bike around some more and it DOES run on both cylinders but something doesn't feel right. My plan is to refer to inspect and change out the spark plugs if needed, and refer to the manual and tune the carbs properly.

    You're right. After riding it a bit more, I noticed that both sides of the head warmed up. I think I just need to tune it properly.
     
  5. xschris

    xschris XS400 Guru Top Contributor

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    The compression should be 125-155 cold. Make sure it's in that range.
     
  6. amc49

    amc49 XS400 Junkie

    X2, 'it has compression' is an invitation to working forever to never fix it. If under 100 psi the cylinder is dead as to making good useable power but that is STILL 'having some'. Engine being too low will sound and act exactly like that. Think about how quick your lawn mower revs up with almost zero compression. Why a 200 cc. engine that should make 20 hp. only makes barely 5.

    The numbers there can and often do kill you. A mech who does not give numbers is a butcher.
     
  7. sandmanred

    sandmanred XS400 Addict

    Check the headers for temperature with a heat gun if you have one. Or use your hands checking from a cold start. That engine sounded really weak and could be running on just one cylinder. Pull the plugs and look at them, that can tell you a lot too. I forgot to put a plug cap back on once and it ran kind of like that.
     
  8. amc49

    amc49 XS400 Junkie

    Oh come on, if you listen to them enough you can ALWAYS tell one cylinder vs. two. I can sync twins doing it. I even got pretty good at syncing threes when it became apparent to me that Kawasaki shops couldn't do it to not miss all over the place.

    Was listening to a new Harley beside me yesterday, I could tell the individual cylinders talking, one slightly behind the other, they almost sound like one but they are not, you can hear the other echo in the sound. Da-duh, da-duh. da-duh, and then dd,dd,dd,dd, as he sped up away from idle. And that's on the same crank pin. And on a now provable bad set of ears.
     

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