Runs fine and then dies and then won't kickstart

[AdamJackson]

New guy here but I am excited that this exists! I have 2 xs400s! A 78' and an 82'.

My 1982 xs400 was running fine before I let it sit for 2 years. Before I ran it this year, i cleaned the carbs and plugs and changed the oil. For the carbs, I didn't adjust any levels and everything I cleaned I put right back exactly as it was. Now the issue is that every time I run the bike, it runs for a little while and then the throttle stops working and slowly dies. The electric start is broken so i use the kickstart but after it dies I can't kick it for the life of me.

Is this an issue with the mixture? did I do something to the float levels? Should I take them back off and give them a bench sync? I really don't know what else I should to and I didn't want to mess with the settings before talking to the pros here! Thanks for any help!

 

[Hishman]

Well i'm uncertain if the same apply to a 4 stroke motor but if a two stroke doesn't get enough oil or runs to lean it heats up and the piston seizes inside the bore. It will unsieze when cooled down.

So sounds like either your oil isn't flowing or its running crazy lean this could be the problem. I can thing of nothing else that would cause the kickstart to sieze

 

[JARichmond]

Before you tear the bike apart, how is your idle screw set? If it's not set properly, your bike will never run well. Giving it a carb sync may go a long way, however. Before I synced my carbs, it would either die slowly or rev up on it's own (dependent on the idle settings).
Point of clarity: The kick-start seizing might be from kicking at compression without enough force. Sometimes it takes me 2-3 kicks to get going.

Also, welcome to the forum!

 

[AdamJackson]

Before you tear the bike apart, how is your idle screw set? If it's not set properly, your bike will never run well. Giving it a carb sync may go a long way, however. Before I synced my carbs, it would either die slowly or rev up on it's own (dependent on the idle settings).
Point of clarity: The kick-start seizing might be from kicking at compression without enough force. Sometimes it takes me 2-3 kicks to get going.

Also, welcome to the forum!

Well i'm uncertain if the same apply to a 4 stroke motor but if a two stroke doesn't get enough oil or runs to lean it heats up and the piston seizes inside the bore. It will unsieze when cooled down.

So sounds like either your oil isn't flowing or its running crazy lean this could be the problem. I can thing of nothing else that would cause the kickstart to sieze

Thanks for getting back to me guys. I thought for sure it was running lean as well but I checked the jets (3 turns out) and the floats are where they need to be. I adjusted the idle screw so that it sits at a pretty 1300 or so. Still, the same thing happens: It runs great then dies after it gets warmed up and I can't kickstart it (the kick start does not seize though, just doesn't turn over). A friend said that it may be heating up and then opening up a crack in something like the intake carb holders and letting air in. Is that possible?
Last thing to do is to replace the plugs and see what happens to them as it warms up and see if its running lean.
If you suggest that the oil isn't running properly, is there something I can do? I gave it a full oil change already with new filter. I didn't take off that little pan at the bottom though…

 

[levdir]

That little pan is the sump plate and there's a debris screen in there that should be cleaned occasionally. It shouldn't be preventing oil circulating though. If you want to clean it, make sure you drain your oil first--I realize that sounds obvious, but I didn't because my drain plug was stripped and it dumped the entire crankcase's worth of oil all over the floor.

 

[xschris]

Jets 3 turns out? No they should be all the way in and snug. The idle mix screws are on the top of the carbs facing the motor. Are yours still capped? If so you will have to remove them so they can be adjusted.

 

[rugbywarrior89]

When did you check the floats? If they have a small leak, it will take a few minutes for the float to fill up and then flood the carbs. Probably not though if you haven't seen gas coming out of your air intake.

I doubt the piston is seizing. If that were the case, you would most definitely feel it when you are kick starting.

If you troll the sight enough you will find that these carbs usually run great when their cold and you won't notice the problem until the bike warms up and then all hell breaks loose. Most likely, you need to clean your carbs again and check them for air leaks, especially around the butterfly seals and the rubber boots connecting the carbs to the engine. I made the mistake of boiling my carbs with the butterfly seals in them and completely disintegrated them. Same goes if you use carb dip. You should have done one of these things. Carb cleaner and blowing it out with air will only take you so far. Many times, including my own, I had to clean multiple times after the bike sat for a long time.

 

[AdamJackson]

Sorry xschris, I meant idle mix screws and they were not capped. I tightened them fully and then loosened both of them 3 full turns. The jets inside the carbs are snug
I just checked the floats again rugbywarrior and there is no gas coming out my air intake. I looked at the rubber boots connecting the carbs to the engine and they are a little cracked. That would be the problem you think? I just finished cleaning the carbs again and there was nothing to clean (just double checked everything).
I may just order new boots and clean them again…

 

[rugbywarrior89]

Cracks don't necessarily mean it's leaking. You can spray some carb cleaner (or WD-40 or anything else that tickles your fancy) around the carb and boots and if the engine noise changes at all, you will have an air leak. If you do buy new boots, avoid MikesXS. They are not built for ethenol and there are a lot of posts around here to the effect. I have also seen people coat the outside of the boots with epoxys like JB Weld or RTV with reasonable success. You can search around on how to do it if you choose the West Virginia method.

 

[AdamJackson]

Great advice rugbywarrior, thank you. I'll check for leaks and go from there.
The question is, if thats not the issue then why would it still be stalling after warming up and then after checking all of the above mentioned things?? It's maddening!

 

[rugbywarrior89]

From 16VGTIDave

Now, for the standard advice to all newcomers - clean your carbs before anything else! Fully disassemble and clean them. When you are confident that they are perfectly clean, do them again! Once you are tired of cleaning them, and will swear on your life that they are impeccably clean, do them again! I'm not kidding...

He couldn't be more right. These carbs NEED to be peak condition, they are very finicky like that. 4 small things that make a difference on these carbs: Valve adjustment, clean carbs, air leaks, syncing them together. I have seen many threads (including my own) where fixing any one of those things completely fixed their issues. Also, invest in a in line gas filter if it doesn't have one already. It's the cheapest preventative maintenance you can do on these bikes.

 

[XS400NJ]

... it runs for a little while and then the throttle stops working and slowly dies... ... I can't kick it for the life of me.

Another new guy here.... this sounds like carb issue or even fuel line , if fuel comes real slow once you burn gas from carbs - you need to wait until fuel seeps into carbs for next run.
But it could also be problem with spark plugs. Before trying difficult things change spark plugs. Also take a look at them after engine "ran for a little and died", are they wet - if they are it's a sign of bad spark plugs?

If you don't have new spark plugs - heat them(electrodes) with a torch until they are glowing red and let them cool, check the gap and put in. If it does not help - go with trying other things.