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New problem with my xs400


heylawnguy
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Hi again everyone. Maybe you guys might have some ideas for me on my latest problem. I rode my new 81 xs 400 for a few hours yesterday and everything seemed good. So today I wanted to take it out again. The battery needs replacing as it does not hold a charge so I have been kickstarting it. So I rolled it out of the garage, pulled the choke to wide open and gave it a kickstart. The bike started right away and after about 30 seconds I turned the choke off. The bike continued to idle nicely. I went over to talk to my kids while the bike warmed up, and after about 3 minutes the bike died. So I went to try and kickstart it again and nothing, it wont start now. I hooked up some jumper cables to make it easier and the bike turns over fine but wont start. I checked the gas level and it was fine but I topped it off anyway. I pulled the spark plugs and put them back on the cable and held the tip close to the heads while cranking and i could see the spark from each plug. I then put my thumb over the plug hole while cranking each side and felt the suction but noticed that my thumb was dry when i remeoved them, I expected there to be gas residue on my finger. I also thought I would see the gas mist out of the spark plug hole while the engine was cranking but nothing. What would cause the bike to run fine then just die and not restart again? Seems like its not getting gas, how should I check this?

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Hi again everyone. Maybe you guys might have some ideas for me on my latest problem. I rode my new 81 xs 400 for a few hours yesterday and everything seemed good. So today I wanted to take it out again. The battery needs replacing as it does not hold a charge so I have been kickstarting it. So I rolled it out of the garage, pulled the choke to wide open and gave it a kickstart. The bike started right away and after about 30 seconds I turned the choke off. The bike continued to idle nicely. I went over to talk to my kids while the bike warmed up, and after about 3 minutes the bike died. So I went to try and kickstart it again and nothing, it wont start now. I hooked up some jumper cables to make it easier and the bike turns over fine but wont start. I checked the gas level and it was fine but I topped it off anyway. I pulled the spark plugs and put them back on the cable and held the tip close to the heads while cranking and i could see the spark from each plug. I then put my thumb over the plug hole while cranking each side and felt the suction but noticed that my thumb was dry when i remeoved them, I expected there to be gas residue on my finger. I also thought I would see the gas mist out of the spark plug hole while the engine was cranking but nothing. What would cause the bike to run fine then just die and not restart again? Seems like its not getting gas, how should I check this?

assuming the obvious that the tank has gas in it, then try setting the petcock position to "prime" which should cause gas to flow directly to the carbs from the tank. if that works, could be a problem with the petcock vacuum. I have problems not getting enough fuel sometimes and can switch to prime and it works ok. I don't think thats a good long term solution, but it helps troubleshoot.

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Hi again everyone. Maybe you guys might have some ideas for me on my latest problem. I rode my new 81 xs 400 for a few hours yesterday and everything seemed good. So today I wanted to take it out again. The battery needs replacing as it does not hold a charge so I have been kickstarting it. So I rolled it out of the garage, pulled the choke to wide open and gave it a kickstart. The bike started right away and after about 30 seconds I turned the choke off. The bike continued to idle nicely. I went over to talk to my kids while the bike warmed up, and after about 3 minutes the bike died. So I went to try and kickstart it again and nothing, it wont start now. I hooked up some jumper cables to make it easier and the bike turns over fine but wont start. I checked the gas level and it was fine but I topped it off anyway. I pulled the spark plugs and put them back on the cable and held the tip close to the heads while cranking and i could see the spark from each plug. I then put my thumb over the plug hole while cranking each side and felt the suction but noticed that my thumb was dry when i remeoved them, I expected there to be gas residue on my finger. I also thought I would see the gas mist out of the spark plug hole while the engine was cranking but nothing. What would cause the bike to run fine then just die and not restart again? Seems like its not getting gas, how should I check this?

just thought of something else.... if battery is dead, then you won't be able to keep enough voltage for the electronic ignition to work. others have posted on that issue, so if you can get it running with jumper cables, you may not be able to keep it running once you pull them off and battery voltage decays below around 11v.

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You can at least troubleshoot that gas gets from the tank to the carbs easily. The carb bowls have a drain on the bottom - if you undo that, you should get about a tablespoon of fuel to flow out. If you don't, then fuels not getting to the carbs. While you're at that, catch that fuel in something, and take a look at it - if it's got crud in it, you've got stuff in your tank, lines, or carbs that could clog things up.

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just thought of something else.... if battery is dead, then you won't be able to keep enough voltage for the electronic ignition to work. others have posted on that issue, so if you can get it running with jumper cables, you may not be able to keep it running once you pull them off and battery voltage decays below around 11v.

even with the dead battery it was starting before when I kick started it. the battery has enough power to make the ignition lights come on but not enough to power the starter. when I tried jumper cables the starter worked fine and the engine turned over but will not start. ichecked the plugs and they are getting a easily visible spark.

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ok so I checked the drain at the carb bowl and there is gas in them. I drained them then put the petcock to pri and the gas started flowing out of the drain. So now I have gas to the carbs and spark to the plugs but it wont start. Any ideas? Should I take the carbs off and blow them out with compressed air?

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I took the carbs off and sprayed them with carb cleaner and compressed air, put it back together and checked for spark again. All seems good but it still wont start. I put a new battery in as well. it dosent seem like gas is getting to the cylinder. I am too much of a newbie to know what to look for in the carb or what to clean, so maybe its a dirty carb? Any more suggestions?

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ok so Being new to carbon cleaning I decided to take them apart and clean them again and sure enough I found some other jets I Missed. So I gave it a good cleaning and sure enough the bike started up on the first try. As a bonus the dead cylinder I reported on is now alive and running strong with the exhuast getting hot instantly. Wow this feels like a different bike now. It has so much torque and the power is amazing. I thoght I was gonna fly off the seat after the first post carbon cleaning test ride. Now I noticed the idle will go to about 4000rpm sometimes and will not go back to normal untill you release the clutch or turn the bike off and start again. I checked the throttle cable and it semms fine and does not stick at all, any ideas.

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ok so Being new to carbon cleaning I decided to take them apart and clean them again and sure enough I found some other jets I Missed. So I gave it a good cleaning and sure enough the bike started up on the first try. As a bonus the dead cylinder I reported on is now alive and running strong with the exhuast getting hot instantly. Wow this feels like a different bike now. It has so much torque and the power is amazing. I thoght I was gonna fly off the seat after the first post carbon cleaning test ride. Now I noticed the idle will go to about 4000rpm sometimes and will not go back to normal untill you release the clutch or turn the bike off and start again. I checked the throttle cable and it semms fine and does not stick at all, any ideas.

I had this problem with mine, and it turned out that the idle mixture was too lean. You can't just go by the number of turns but need to either use a colortune or adjust by ear (adjust the screw out a little on each carb as long as the idle speed goes up keep going, then when it starts to drop off again, go back down slightly). Once adjusted correctly (and you WILL need to reduce the idle speed screw as you do this) it will drop right back down every time.

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I've also noticed having the idle stop set too high definitely aggravates this. The RPMs don't drop down nearly as quickly when I have the throttle stop set to give me 1500+ when the bike is FULLY warmed and has a warm ambient temperature. Having the idle stop set for 1200 RPM FULLY warmed means that it runs really low on a cold morning with no choke when I first start it, but I usually only warm it up for about 15 seconds or so before driving off (4 seconds full choke, 8 seconds half choke, then no choke with a little throttle and down the driveway I go).

This (from your other thread) clued me in (unless you're restarting a warm bike...):

I start the bike and sometimes it will idle fine around 1200 rpm then it just starts getting higher and higher untill you turn off the bike. Reving the throttle does nothing to help.

Just can't set the idle stop with anything other than a tuned, warmed up bike it seems.

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