xs400 blue smoke from carbs

[Richardb]

Hi all,
I have a recently acquired 1980 xs400 special with 16k miles. the bike seems to run and start well, but with a few issues. 1) slight oil leak, (only a few drops at a time). 2) idles normally at startup, but will creep up to around 3000rpm after the bike has warmed up. 3) also after the bike has warmed up, i get blue smoke coming from the air intakes (none at all from the pipes)...
I have been told it could be a leaky intake valve, but it doesn't seem to be affecting performance, so I am lead to believe I'm still getting good compression. if it is a bad valve, how would i go about checking this?

thanks,
rich

[petejw]

Hi Richard,
Welcome to the forum.
Im not to familiar with the 400's but
with regards to your problems, with the high idle, once the bike is warmed
up and the idle rises reset set it back using the idle screw to the stock setting. When the engine is cold its not unusual for the bike to idle really low.
The blue smoke if its coming from around the air box you'll probably find that the engine breather hose has come away from the air box. Depending on how bad the smoke is it could indicate worn rings or a rich mixture can also exhasberate the problem. A compression check will help determine how good the engine is.
Hope this helps you a bit.

[Richardb]

thanks! the problem was indeed the breather hose, and an idle adjustment helped a lot too. running much smoother now.

rich

[petejw]

Good to hear you got it sorted.

[cywelchjr]

Hi all,
I have a recently acquired 1980 xs400 special with 16k miles. the bike seems to run and start well, but with a few issues. 1) slight oil leak, (only a few drops at a time). 2) idles normally at startup, but will creep up to around 3000rpm after the bike has warmed up. 3) also after the bike has warmed up, i get blue smoke coming from the air intakes (none at all from the pipes)...
I have been told it could be a leaky intake valve, but it doesn't seem to be affecting performance, so I am lead to believe I'm still getting good compression. if it is a bad valve, how would i go about checking this?

Where is the oil leak coming from? I happen to have one of these things and have had a lot of experience over the last 2 years getting it back in decent shape. Where the oil is coming from can tell which seal/gasket/plug needs replaced (pretty much all of which are still available strange as it may seem).

If you get a high rpm hang when fully warmed just adjust the idle mixture, these things were incredibly lean from the factory and on todays gas it's just too much, richen it out some, and it will be better.