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78 xs 400 E rebuild and modify

Discussion in 'The Garage' started by Tyler Shiells, Mar 30, 2017.

  1. BBS360

    BBS360 XS400 Guru Top Contributor

    That is just for the reservoir, not the cylinder.
    There are no rebuilt kits for the rear master cylinder.

    That's a good seller though. They have a website too.
  2. So I ordered caliper rebuild kits, front back. Got a pair of uni pod filters and a few sets of jets. Also picked up a 1.3amp 12 volt battery.

    First off, I can't get any fluid to pump out of the rear master cylinder. I can hear and feel air pressure coming out the line but fluid want pump through . Any ideas?

    I installed the pods and went one size up on the jets. Except the bike won't kick over with that small battery. It starts fine with a 6 amp. Any ideas there?

    I haven't synced the carbs yet with a manometer but when it warns up it wants to hang high on the revs. Hope a sync will cure that.

    I did drive it around the property
    No brakes tho. But the transmission does seem fine.
  3. BBS360

    BBS360 XS400 Guru Top Contributor

    Can't go too much smaller than stock and still use the starter. Go with a larger size or give up on the starter.
    Hopefully, but hanging RPMs tend to be a sign of running lean.
  4. I'm only running the kicker. My starter selonoid was shot and it's cheaper just to run a small battery with the kickstart only.

    Lean? OK. I'll up the needle position and try the next size jets.
  5. I did get the rear master cylinder to prime.
    I also replaced all the gaskets on the rear caliper.
    Now I am having leakage past the caliper piston, with seals installed.
    What cause this? Pitted caliper piston?
  6. 20170623_184910.jpg 20170623_184920.jpg

    That's the condition of my caliper pistons.
    I can prime the master cylinder, bleed the lines of air, but the caliper just leaks around the seals. I've replaced those.
    Are those pistons that cause of the leaking? Should they be replaced?
  7. agent laraby

    agent laraby XS400 Enthusiast

    Those caliper pistons are cooked old fruit, plenty of replacements on ebay. . Check your caliper wall as the scale on the pistons can cause scoring .
  8. Thanks
    I did order new ones from Yamibits. Just waiting to be installed.
  9. A new problem has arisen. I did have the bike running, not great. But now I can't get it to start. I was going to sync the carbs but nothing. I took the carbs apart cleaned em again and set the float height. I can kick it about 30 times and only get a few sputters here and there and a maybe a pop or two. Almost like it's flooded.
    I want to check the fuel level but these carbs don't have a proper nipple and drain screw on the bowl and a hose just doesn't want to stay on the drain plug. How do you guys work around that? Maybe my floats have become saturated, now that they have sat in gas for awhile....
    Going to pick up new plugs tonight. The spark on these ones does look yellow and dull. Hope that's all it is.
  10. Replaced the plugs to no effect. Still just sputters once or twice in 30 kicks. Or kinda makes a coughing sound. The only thing I can think of is the floats are shit and have become saturated. Is there any tell tale signs of a bike being flooded? The gas isn't coming out of the filters.
    I'll pull the floats and see if they float.
    Wish these carbs had the nipple and screw on the bowls.
  11. BBS360

    BBS360 XS400 Guru Top Contributor

    Pull the plugs to see if they're fouled with gas.
    Not brass floats?

    It's still not quite as easy as on later models but for viewing float fluid levels you can get a grease nipple with the appropriate thread pitch for the drain screws, pop out the integral valve, shove a clear tube on it, and screw it into the drain.
  12. I will check the plugs for gas.
    Yes they are brass floats. I just thought that now that they've been submerged in gas for a few wks, and if they were deteriorated in any way, they would have become heavier. Not sure if that's even possible.

    And thanks for the tip on the float level tool. I'll have to acquire the necessary piece.
    Last edited: Jul 1, 2017
  13. BBS360

    BBS360 XS400 Guru Top Contributor

    There was a guy selling such a hose tool but it seemed expensive for what it was.

    Give the floats a shake, if they have a leak you'll hear gas sloshing inside.
    I recently had to replace one of mine. My soldering iron repair wasn't working and the soldering torch may have exploded the float.
    Quite literally.
    Didn't think that one through.

    Chasing a flaming float as it rolls across the carpet, dribbling bits of flaming gas, is not an experience I'm going to repeat.
  14. spectra

    spectra XS400 Junkie Top Contributor

    I want pics as it rolls across the carpet :D
  15. I will follow that sage advice. Lol
  16. This is how the bike currently sits.
    I did it get it to fire up again. For some reason fuel wasn't getting to the carbs.

    I made a custom Gorilla tape seat. Just for use around the property, till I make a new one.
    Rear brake is fully rebuilt and operational.

    I tried to sync the carbs with a manometer but it still revs up to 4000 when warmed up.
    I'm up one on both jets. Maybe go up on the needle?
    Can't figure out why it still wants to run lean. Could old diaphragms cause this? They look to be good. How bout the seals around the choke plungers? Can those leak?
  17. BBS360

    BBS360 XS400 Guru Top Contributor

    Might have been mentioned previously but have you changed out carb jets?
    It'll run lean with those mufflers.
  18. Yep. I went up one on both the main and pilot jets. I have the next size to try.

    I guess those aren't the factory mufflers?
  19. Well went up 2 sizes on the carb jets and the needle is set at the bottom slot. Also the pilot screw is 4 turns out. Still revving up to 4000rpm when warmed up.

    I'm going to have to replace the seals around the chokes to rule that out, before I go up anymore on the jets.
  20. I notice I have an oil leak from behind the timing cover. I assume that's the seal around the cam shaft?

    Also decided to better inspect my points. Since i pulled the cover off. One they weren't gaped properly and have some pitting on the points. Would that cause the high idle after warm up?

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