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80 XS400 high idle

Discussion in 'The Garage' started by mikeasis, Mar 29, 2019.

  1. mikeasis

    mikeasis XS400 Member

    thank you.
    Im wondering if I need to remove these and the mixture screws and blow out those passages again. Are there o-rings that would need to be replaced if I do this?
     
    Last edited: Apr 14, 2019
  2. Needle and seat can be tested with air usually. I used siphon to pump some air in to ensure it resisted.

    Generally any ring around needle means replacement time. Believe the may be YouTube about a cheap attempt to avoid that by somehow resurfacing needle to renew the surface as a flat angle but that may be temporary fix or a fruitless effort when brand new ones exist on sites like Mike's XS and Amazon.

    Manual is incorrect about float height
     
    Last edited: Apr 16, 2019
  3. mikeasis

    mikeasis XS400 Member

    Ordered Yamaha needle sets. Ill let you know how it turns out in a few days
     
  4. mikeasis

    mikeasis XS400 Member

    installed some used bars (found them to be bent by the way) and bam the starter works. Then it didn't, wiggled the wiring and it works again. oh well the bucket is coming out anyway sooner or later and Ill have a better look at everting behind it. I got one float set, yea one and it was described as 2 with pics of 2. Waiting to hear from the seller on this one.
     
  5. mikeasis

    mikeasis XS400 Member

    I got my second needle set a few days ago and finally had time to install them. I then set the pilot screws to 3 turns out. First they helped as im no longer flooding out the bike and I can restart with no issues. BUT it still wants to take off on me but only when warmed up. I fired it up cold and I can rev it up as much as I want and it settles down nicely, but if I take it up the block and back and get it warm, it wants to keep revving, like 3K. I tried brake cleaner and Carb cleaner around the intake joints, carbs and along the head gasket couldn't get it to do it.
    Its like something is getting hot and causing this. Could carb o-rings or diaphrams do this? Could the ignition fail advanced when hot?
     
  6. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    You could be leaning out when the engine warms up. What do your plugs look like?

    You should do all of your fine adjustments with the bike warmed up after a ride. Syncing the carbs can be tricky too.

    Of course, after you set everything on a warm bike. Your cold idle will not be perfect, but thats why you should usually always need the choke/enrichener to help the engine idle where it needs to.

    Idle when hot should be around 1200 rpm.

    I had a high idle due to airleaks at the throttle shaft seals, then sometimes the throttle would stick a little.
     
    mikeasis and buztabuzt like this.
  7. mikeasis

    mikeasis XS400 Member

    I think im going to send the carb out and have them rebuilt.
     
  8. xschris

    xschris a lifestyle not a trend Top Contributor

    Is that a crack in the body under the fuel inlet and near the "MIC" mark?
    20190414_185133.jpg
     
  9. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Dont send them out.. send them to me!

    Im seriously considering offering a carb rebuild service for XS400 members..even though i strongly recommend you do it yourself.

    The carb body does look cracked though. I have a set of carbs from my 79(?) that i will probably never use because I only use XS360 carbs. May consider rebuilding them and letting them go.
     
  10. mikeasis

    mikeasis XS400 Member

    I had suspected it could be but that it could be casting flashing also. Ill hit that area again with carb cleaner while running before removal.

    I went out and inspected further I don't think it cracked, it seem to scrape away with the finger nail.
     
    Last edited: May 3, 2019
  11. mikeasis

    mikeasis XS400 Member

    Im good with engines, reasonable with electrical. Its one thing when electrical gremlins get you but when something that operates on the same principles as a toilet bowl get you....Im no carb guy. I can clean up and setup a single carb to factory settings but with multi carbs meehh. I think with these Im intimidated by the throttle shafts and getting them reinstalled correctly. That and where to get the correct O-rings.

    pulled a plug, white in color so for sure lean
     
    Last edited: May 3, 2019
  12. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    You can bench sync the carbs and that should be OK to get the bike in a a better running state. I use a guitar string, a B string will work

    Open the throttle a bit and let the butterfly close down on the string. Next, you will get another piece of string and set the other carb so that the butterfly closes on the string BUT, doesnt pinch the string too hard. That is a bench sync. One carb is the "master" and the other carb is set to the master. Then you do a sync with manometer.

    Getting to the throttle shaft seals is the hardest part of a full carb rebuild. The carbs have to be completely gutted.

    The butterfly screws are staked to the shaft. So they are basically one time use. You get new screws with the bushings and the new screws MUST be red locktite or staked so they dont fall out and get pulled into a cylinder.
     
  13. mikeasis

    mikeasis XS400 Member

    I just went out and fired it up. Fires up good with the choke idles up then I push in the choke. it settled down and idled around 1500. I sprayed a full can of carb cleaner all around the throttle shafts, the crank case vent, intake port and fuel shutoff just for measure, head and base gasket with no change in idle. The bike at this point is warm. I rack it off and boom doesn't want to sit below 3500. I put it in gear and let out the clutch slightly until it almost stalls and its runs right back to 3500. Its like the throttle is sticking but its not. its fully released and the choke in. when I had the carbs off I operated the slides and they seemed to move nicely with no sticking.

    I would have thought I would have found an intake leak with all the spraying I did.

    Edit I just ran a compression test and obtained 135ish at WOT. I belive this to be to low ;(
     
    Last edited: May 3, 2019
  14. xschris

    xschris a lifestyle not a trend Top Contributor

    Set your valves. Warm bike up and sync the carbs with a manometer. Make sure you have correct air boxes/filters and intake hooked up. Set you idle mix screws to 3 turns out from seated. If your high idle is still there check the carb diaphragms for cracks or holes. 135 cold compression is still ok. 150+ is new. A valve adjustment and some good long riding my help bring numbers up. You carbs still look to have varnish in them. This could also be blocking ports.
     
  15. mikeasis

    mikeasis XS400 Member

    I really appreciate all the help.

    I checked the valves and most were to tight with one intake valve that was very tight. I rolled the motor over several times and kept rechecking until I was happy with it.

    Bike has aftermarket intake manifolds that each have ports. Left capped off. Right feeds the fuel petcock.
    Found OE carb to air box boots on ebay. Nice and pliable no cracks. Center section is harder plastic with a crank case breather hose to crankcase .
    Stock style air filter replacements.ive sprayed around clamps with mo change in idle
     
  16. How many turns are you on mic screws as Chris asked? Experimented with this yet?
     
  17. mikeasis

    mikeasis XS400 Member

    Yes 3 full turns out. The 2 things that seem to have made any difference was the valve adjustment, much quieter and the needle seats, no longer flooding.
    I have not tried any more adjustments on the mixture screws
     
  18. xschris

    xschris a lifestyle not a trend Top Contributor

    Synced carbs with manometer? Check for holes in diaphragms?
     
  19. mikeasis

    mikeasis XS400 Member

    no I didn't sync the carbs as I didn't think I could get correct results with whats going on. I did inspect the diaphragms and held a small light behind them looking for holes.
     
  20. xschris

    xschris a lifestyle not a trend Top Contributor

    A carb sync with a manometer is a must. It will balance the carbs perfect. It can make a huge difference in how the bike runs.
     

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