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First Bike!

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

  1. 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
    tostentr and buztabuzt like 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.
    AViciousCorgi and buztabuzt like this.
  5. I am finally getting around to working on this bike!
    I am ordering parts tonight, carb rebuild kits (probably from mikesxs) and bigger jets (two up on the main and one up on the pilot since I have a MAC 2 to 1 and pod filters), and OEM style carb boots. I sprayed the carb boots with wd40 and did not notice a difference in idle, but realized the carb boots are not the OEM style. I also have some performance carbs that came with the bike, I believe from mikesxs and the current carb boots on the bike are from that kit. The original owner could not get them working correctly.

    Since my last update I have installed and partially wired up the gauges, wired the license plate light and have also installed the bar end mirrors.

    Other things id like to fix/modify over the winter: seat hoop, rewire/battery relocation, shave off tabs on the frame, repaint the frame and possibly the tank, tray under the seat for the electronics and battery.
    tostentr likes this.
  6. XSLeo

    XSLeo XS400 Junkie

    These carbs and several variations of them were used on a lot of different bikes. Very few used the same internal parts as far as jets and such. Most of the carb kits you get seldom have the parts you need. Gaskets and maybe float valves will work but not much else.
    I as well as others don't recommend carb kits. Do the tear down and cleaning first. This way you can buy just the parts you need.
    If you are careful on the tear down you can reuse the gaskets. Clean every thing else up good so you can see if worn.
    On jets, Mike's sells off brand jets that are not as good as genuine Mikuni jets yet charges about the same price.
    Jets-r-Us or Niche Cycle sell genuine Mikuni jets.
    What Kind of pods are you getting? CV carbs tend to have tuning issues when using the K&N pleated element type of pods. The shorter and more tapered the more the issues.
    These pleated element pods cause excessive air flow turbulence through the carbs which causes a poor vacuum signal from the slides. This slows and delays slide lift. This causes off idle flat spots as well as steady cruise variations.
    A long foam filter element pod has a smoother air flow and eliminates these issues.
    Those performance carbs from Mike's are a poor choice. A few that got sold early on worked ok. I think these were made by a good supplier. Once they started to sell Mike's started getting knock offs made in China. These are not very good carbs.
    I was reading one fellow struggles to get them to work. After months of work and over $600 in parts he got them so-so.
    They now set on his shelf.
  7. I have EMGO filters. I think I'm going to go ahead and clean up the original carbs. I have done research about jetting size for my year (78), but I guess I'll attempt to tear them down and clean them this weekend and figure out what I need, if anything. I have never messed with carbs before!
  8. sandmanred

    sandmanred XS400 Addict

  9. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    XSLeo is right about the off-brand jets. You have to go Mikuni. Jets R Us has everything you need as well as Sirius Consolidated Inc.

    I looked at an off brand main jet and a Mikuni jet with a digital microscope/optical comparator at work, and the off-brand jets had rougher surfaces and a totally different design. The off brands were much smaller compared to a mikuni jet of the same size.

    If you are using the PRIME or RES position, you will probably start pulling in debris from the tank since it takes fuel in at the very bottom of the tank. Make sure you turn the fuel supply off when you park it.

    Theres Harley people that run CV carbs on their bikes and they make it work just fine.. I bet if you fashioned up trumpets that were maybe 10" long, that might do something. Theres gotta be a way to make it work and maintain the cleaner look. Nothing is better than stock and thats how I have mine. I dont care what it looks like, nobody else cares or even notices, my leg is covering that spot anyway. I commute 90 miles a day mostly highway miles at 75 mph so its gotta perform at its best.
    AViciousCorgi likes this.
  10. tostentr

    tostentr XS400 New Member

    Can't wait to see how it turns out! Good luck!
  11. XSLeo

    XSLeo XS400 Junkie

    www.amckayltd.com/carbguide.pdf was written by the carbs gurus over on XS650.com. The later BS34 carbs are vey similar to the XS400 BS34's. Main difference is the XS400 has the fuel inlets on the out side and throttle cable/idle speed between the carbs. XS650 opposite.
    Jetting will vary also.
    As far as the tear down they are pretty much the same.
  12. Ok everyone, here is my weekly update:

    I pulled apart the carbs. It was fairly easy even though it had a stripped screw at the very top of the carb. The carbs definitely have been torn down by the previous owner. The inside of the carbs are incredibly clean, with several like-new parts in it. The main jets are 152.5 (WOAH) and the pilot jets are 145. I can't imagine that the mains need to be that big, so I will probably order 147.5 mains. The bike did seem like it was running rich but I'm not sure if that has to do with the main jets. I am also going to order a set of gaskets, the gaskets currently that are in there are a little....crusty.

    BTW, here are some more detailed pictures of the bike to show you what I am working with. I did not take any pictures of the stripped-down carbs.

    Battery.jpg Carb Boot.jpg Center Bars.jpg Electronics.jpg Exterior.jpg Inside Headlight.jpg Petcock.jpg Right Carb.jpg Left Bar.jpg Right Bar.jpg
  13. xschris

    xschris a lifestyle not a trend Top Contributor

    Ditch those pods as they are the worst setup for these bikes. Find a stock set of air boxes and H-pipe. That setup work the best for these bikes.Or at least use a stock H-pipe and some foam uni's at the ends. Get some stock intake manifold boots. I am not sure what you have and that they don't have any vacuum barbs for syncing the carbs. Go back to a stock jetting and go from there. Most people way over jet these bikes. Another thing to look out for is to make sure your pilot mix screws have not broken off into the carbs. People will over tighten them snapping the tips off. Getting them out can be very hard. Some will use larger than the hole size drill and destroy the carb. You would need a set of micro drills and use a lot of caution. It can be done but it's not easy.
    Last edited: Oct 25, 2019
  14. I have to say I am definitely going for a brat/cafe racer build. I rather like the pods so I may go for the uni's. I already have bought the OEM carb boots to replace whatever what's already on the bike. I checked both the pilot mix screws and they are not damaged or anything thankfully!

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