Engine will not idle down

[joebeets]

Yea,

79 xs400 sat in a barn for 12 years pulled the carbs. invested in a carb rebuild but everything back together and actully ran. I'm impressed..... The only issue is motor will not idle down. Any ideas out there....

 

[HoughMade]

What are the idle screws set at? 3 turns out is a good place to start. Does it not respond at all to the idle air screw?

 

[ThePsuedoMonkey]

Mine did that for a few days of running after my rebuild, but only when the fuel level was low (1/4 tank or less). I'm not sure what the issue was but it apparently went away on it's own. The idle adjust knob worked, but it would still idle at ~3k. I did find out that it was running lean though...

 

[eric123]

Lean, maybe an intake leak. Are the carb holders in good shape?

 

[xschris]

Sometimes the idle screw ends get broken off in the carbs. You can check this by pulling them out and seeing if the ends are still pointed.

 

[OleDoc]

my 79 had a similar prob.the carbs throttle butterflys weren't synced.the left one was partially open at idle,making it idle at about 5000 rpm.

 

[daw dubsack]

I just got my xs400 to run today and I have to get my idle down as well

 

[HoughMade]

Assuming the carbs are clean...and that's not really a safe or realistic assumption, idle is adjusted with the idle air screw (first pic), but if it is adjusted to 1200rpm and them climbs up as the engine warms, it is usually a sign of a lean fuel mixture. This is caused by dirty carbs, an air leak or the idle mixture being too lean. The second pic is the idle mixture screw, one on each carb. Start at 3 turns out from a very, very light seat and adjust from there.