runs then dies

[hardleydavidson]

I bought a non running 81 xs400 off of craigslist and have been trying to get it going again. New battery, clean carbs, fresh plugs. When I fire it up it fires up right away and runs strong (no dogging, good throttle response) but it only runs for about a minute or two then dies. If I try to restart it right away it wont start but if I let it sit for a bit itll fire up again. When it runs the idle is inconsistant, revs high hangs then drops acts like it has an airleak but when I blast the manifolds and around the carbs with starter fluid it dosent effect it. Im running an IV tank so I know its not a clogged fuel vent. Fat healthy spark to both sides, when it dies I tried cutting the gas supply and then cracked the float bowls and a good stream of gas poured out so I know its getting gas. was originally running some crappy autolite plugs which kept fouling so I replaced them with a hotter BP6ES NGK. Now they dont foul but that didnt solve the problem. Ideas? starting to bang my head against the wall!

 

[hardleydavidson]

one other thing I just noticed is that I have to have the Idle adjust all the way up to get some semblance of an idle

 

[mogie]

i would check the mixture screw adjustment. Mine had a similar problem, would run but idle high then stall. mixture screws were 1 3/4 turns out and i adjusted to 3 1/2 turns out then adjusted the idle to 1200 rpm and runs great

 

[corruptmind]

Are you starting it with or without the choke?

 

[HoughMade]

I know you said the carbs are clean.....but what exactly did you do to clean them? This could be important.

 

[hardleydavidson]

It'll start up with or without the choke but once running the choke kills it. When I cleaned em I disassembledthem, soaked them in berrymans carb dip, washed them off with hot water, then blew through each jet and carb body passage with compressed air.

 

[drewpy]

did you get the passage in the float bowl?

 

[DanMach]

I'd check a few things...

1. Your petcock. Get a transparent fuel filter, or just a transparent bit of hose and watch the fuel flow as it idles. It might just stop suddenly and the bike dies a bit after.

2. The floats on your carb. They could be a bit off and allowing the float chamber to under fill and thus it runs ok with throttle but then when returned to idle it suddenly dies.

3. It could also be an an electric part over heating rapidly..

In short: Start it up, as soon as it dies, check float levels and spark.

 

[hardleydavidson]

Thanks All! think I got it figured, went through the valves and they where all outta wack, dialed those in and now its running a lot better

 

[DanMach]

Son of a bitch! the *one* thread I don't suggest valves.

 

[maseworth]

I've got the same problem. Can you explain what you did to the valves?

 

[226dark]

Valve gap/clearance to spec. Those 4 round valve covers on top of motor. 17 mm wrench i think - and feeler gauges, and a manual. Smaller wrench and flat blade screwdriver to adjust the clearance.