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Bike runs with choke out revs with choke out. Will idle weakly with choke in. Dies when I try and re

Discussion in 'The Garage' started by John C Hannah, Nov 21, 2019.

  1. To me , it seems like it's not getting enough fuel without choke. I've tried to pull out the fuel screws to 2.5 turns and even 3. Doesn't seem to be helping. The bike wasn't running for who knows how long , I cleaned the carbs, and even replaced the pilot jets. With the same size, 42.5. it's an 81 single over head cam with 2 into 1 exhaust xs400.

    What could I be missing ?
    Last edited: Nov 21, 2019
  2. xschris

    xschris a lifestyle not a trend Top Contributor

    The bike should rev high with the choke pulled out after it warms up. That is when you need to push it in. What do the plugs look like. You may just need to adjust the idle. With stock intake and exhaust I run 3 turns out on the pilot mix screws.
  3. Good question, I'll take a look at the plugs , I just put clean ones in, but they might have gotten fouled when I first got it running. Let me ask you this, do the xs400s have washers and o rings at the bottom of the fuel mix screw? I know the 650 does.
  4. xschris

    xschris a lifestyle not a trend Top Contributor

    Yes for the 80-82 sohc bikes. They use the same ones as the 80-84 xs650 bs34 carbs. o-ring, washer, spring, screw. In that order.
  5. Hmm, where is a good place to get replacement washers and o rings, mine are missing them and I'm getting a few pops . I've been getting it to run if I very slowly let on the throttle. It's a little choppy in the first 25% of the throttle
  6. xschris

    xschris a lifestyle not a trend Top Contributor

    Post a pic of your carbs to make sure you have the correct year. Mikesxs has them. Ebay has them also listed for o-rings. Using 80-84 xs650 you should find them. I have washers if you can't find them.

    Attached Files:

  8. xschris

    xschris a lifestyle not a trend Top Contributor

    Those are stock 81 carbs.
  9. XSLeo

    XSLeo XS400 Junkie

    With missing parts that is probably the issue. With out that I would say your carbs are still dirty.
    I'm over on the XS650.com site as well as on here.
    They have a carb guide written by their carb guru's. www.amckayltd.com/carbguide.pdf The XS650 BS34 carb are very similar to the XS400 BS34 carbs, The carb guide's tear down, cleaning and inspection methods apply to your carbs. Specs for jetting are a bit different but you can find the stock specs on here are a good place to start.
    Over there we have found that issues such as you describe are often dirty carbs. Particularly the idle circuits. These circuits have passages and tiny outlet holes that plug easily.
    Some not familiar with these carbs may need to go through them several times to get everything.
    Once you get the carbs clean, replaced what is missing or worn the carb guide has section titled "Tuning For Mods" This same procedure will help tune your carbs even if it's all stock.

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