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First Bike!

Discussion in 'The Garage' started by AViciousCorgi, May 8, 2019.

  1. AViciousCorgi

    AViciousCorgi XS400 New Member

    Hello everyone,

    I recently got my first bike which is a 1978 xs400. So of course like all people, I searched the internet looking for parts, cool builds, and general knowledge. I so happened ran across this forum!

    Anyways, the bike already had some work done to it but needs some more work and parts. It has around 10,000 original miles. I have already ordered a slew of parts such as mirrors, gauges, pod filters, etc.

    I have already installed a rear LED taillight and a license plate mount.

    Work that needs to be done:
    I know I will have to re-jet the carbs for the pod filters and I have not the first clue on what sizes to go for.

    The guy switched out the air intake tubes (the tubes that run from the carbs to the engine, not quite sure what these are called) and it deleted the vacuum line for the petcock valve. He installed a fuel cut off switch and just used the prime setting on the petcock valve. Is this bad for the bike?

    I have only ridden the bike once and noticed that once it warms up the idle is pretty high. I'm not quite sure if the carbs just need to be cleaned or if there is an intake leak.

    But here's a couple pics of the bike!
    xs400.jpg xs400 1.jpg
    Last edited: May 8, 2019
    buztabuzt likes this.
  2. Lepp

    Lepp XS400 Member

    Make sure the vacuum ports on the intake manifold are capped off. And I just put pod filters on mine I went from 42.5 pilot to a 45 and 135 main to a 137.5 and it runs great but I found that pods don’t work right with the vacuum style petcock but my new tank is a normal style petcock and I just capped the vacuum ports n it runs good
  3. Search the forum some. Nothing inherently wrong with using prime as long as you always turn it off after. Otherwise must have vacuum connection between gas tank and carb boots
  4. XSLeo

    XSLeo XS400 Junkie

    On Pods a lot depends on the type of pods you get. On CV carbs the short tapered pleated element pods don't work well. They tend to give you tuning issues. A flat spot just off idle and when the slides start to lift.
    This type of pods causes excessive air flow turbulence as it passes through the carb. This turbulence causes vacuum fluctuations that delay slide lift.
    Longer straight pleated pods may be better. A lot of us not using the stock air box use long straight foam pods. This type of pods greatly reduces the turbulence in the air flow. This eliminates a lot of tuning issues.
    When it comes to carb tuning starting with clean carbs is important. Over on the XS650 sister site they have a carb guide. www.amckayltd.com/carbguide.pdf the later XS650's use a BS34 carb very similar to the XS400 BS34 carbs. Some of the specs may not be exact but the procedures are the same. Follow the steps to tear down, clean, inspect your carbs. This way you can determine just what parts you need.
    Kits often come with generic internal parts. The brass stuff. Most of what's inside can be used. If you are careful on the tar down the gaskets can be used.
    There is a section in the guide titled "Tuning For Mods" This works for most any bikes. I would start with getting a selection of jets. One and two steps up on both the mains and pilots. This way if you need them you will have them and not need to wait.
    Often with just changing the air filters one up works. If changing the exhaust one up often works. If doing both two up often works. Some times you might even need to go three up on the mains.
    Basically tuning requires you make one change, test, make another change test. Making two changes at a time is not recommended, it makes telling which change worked.
    Running a vacuum petcock using ON as Off and PRI as on won't hurt the bike. the only really bad thing is the PRI position is you have no reserve. If have to watch your fuel level in the tank closer so you won't run out of fuel.
    buztabuzt likes this.

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