1982 XS400 Starts Sometimes, Not Others

[tjcar]

Hi guys, new member here, first bike I've ever owned.

Bought this bike for $400 off craigslist about a month ago. It was running on one carb, so I took them out and gave them a thorough cleaning while replacing the float valves and needles. Put the carbs back in last week, fed them some gas, bike ran great. It idled smoothly until it ran out of gas.
Had to put a new front tire on, so I had no reason to start it for the past week. Now when I go to fire it up it only sometimes turns over for about 5 seconds and shuts off on its own. When it does fire up, the choke is off and the throttle is halfway open. releasing the throttle causes it to shut off. Also, it only starts up after it has been sitting for an extended period of time. I cannot figure out what is wrong with it, maybe it is getting an improper amount of gas. The petcock is on when I do try to start it.
I considered it flooded, so I drained the carbs and turned the petcock back on to start it up.

I am thoroughly stumped as to why it ran great a while ago and will not run anymore. Does anyone have a suggestion as to why it won't run? Is there a certain amount of gas that needs to be in the carbs?

Replaced the spark plugs too this morning.

 

[NewHavenMike]

Welcome,

Theres a lot of problems that could be going on. Did you set the float height? Does the petcock flow gas freely? I bet you didn't clean your carbs well enough. It can take a couple tries to get it good. Most of us have been down this road a hundred times, its usually the simple things.

 

[tjcar]

I did not set my float height. Will look up a thread for that. When I cleaned the carbs I left them in a gallon of carb cleaner for a week then blasted them with compressed air. Tomorrow I think I will take the carbs out again and make sure all is good.
Petcock does work. Thanks for such a quick reply.

 

[xschris]

To clean carbs you need to FULLY disassemble them and clean every part making sure every tiny little hole is clear and clean. Did you remove all the rubber parts in the carbs before you dipped them? If not you most likly destroyed them (diaphragms, butterfly shaft seals, mix screw o-rings)

 

[tjcar]

I did disassemble them completely. Diaphragms look good, got some new o-rings too. Going to double check tomorrow.

Appreciate your dedication to these bikes man, impressed with your lineup. Thanks for reaching out.