I have a 1981 XS400S which I just replaced the throttle cable in. The bike started on first kick and ran beautifully beforehand. After I got the tank back on and everything together it started just fine and idled for a bit then shut off. After that it was very hard to start and only ran for about half a minute before it stalls. If the bike sits for an hour or so bike will start back up. Any suggestions?

Sounds like a fuel feed problem. Switch the fuel tap to Prime and see what happens - if it's OK like that, then that suggests the vacuum take-off isn't doing it's thing. Or ... a blocked fuel cap breather - run it with the cap open and see if that makes any difference. Or ... a blocked fuel pipe/strainer, shifting the tank may have dislodged some crap.

Just a few thoughts.

You're welcome

Fuel flow is good when I switch it to prime.. I tried running it with the fuel cap open and nothing changed.. Can I take the petcock off and see if anything is blocking? This is my first bike so I'm kinda feeling my way around here..

*edit: so yea the petcock doesn't let anything flow on prime, it flows when i switch it to reserve. Do i need a new one?

Have you kinked the fuel pipe when you put the tank back on?

Fuel flow is good when I switch it to prime.. I tried running it with the fuel cap open and nothing changed.. Can I take the petcock off and see if anything is blocking? This is my first bike so I'm kinda feeling my way around here..

*edit: so yea the petcock doesn't let anything flow on prime, it flows when i switch it to reserve. Do i need a new one?

if the worst comes, you can buy gasket kits to repair and clean out the tank at the same time!!

I don't think its kinked, i mean its bent but that was the first thing I checked. I'm really hoping I don't have to rebuild the petcock or anything, I really want to ride a few more times before the snow :-/

*edit: so yea the petcock doesn't let anything flow on prime, it flows when i switch it to reserve. Do i need a new one?

OK, I'm going to go with the obvious here - what position is the fuel tap in when you try to run the bike (and it splutters to a halt)?

the first time it was set to ON but the other times i get it to turn on its set to Reserve. There is plenty of gas in the tank too..

*edit: so yea the petcock doesn't let anything flow on prime, it flows when i switch it to reserve. Do i need a new one?

This statement suggests you have run onto reserve

the first time it was set to ON but the other times i get it to turn on its set to Reserve. There is plenty of gas in the tank too..

This also kinda does...until you say theres plenty gas in there

or it may have a blocked mesh screen on the longest tube from the petcock inside the gas tank.

Its wierd, setting the petcock aside, even though gas flows the bike does not start. We tried starter fluid, popping the clutch and 100 kicks on the kickstart. Gas is getting into the carbs but doesn't seem to be going through. Am i going to need to rebuild the carbs?

so you tried starter fluid...............and?

we sprayed the starter fluid and tried kicking it but nothign happened. When we tried to pop the clutch it burned off the fuel but opening the throttle didn't do anything...

I can only assume that 'pop the clutch' means bump starting to us this side

well pop the clutch then remove the plugs, are they wet with fuel?

A compression test might be appropriate too! or failing this,,,squirt some oil into each cylinder and try again to bump start the bike, this should improve the compression if its low and can sometimes help start a worn engine

Well its dark and cold where I am so I will try that tomorrow.. I'm assuming if they are wet then the carbs are fine and if not then they are in trouble?

*edit; Sparkplugs are getting gas to em, they are alittle discolored but theres no buildup or anything. Battery seems to have died, so its charging. also there was a tube that was supposed to go to the top of the petcock that was not on. so after battery charges I'm going to give it another go

*editx2; So battery charged and all hoses in place bike starts and runs fine! Thanks for all your suggestions