valve seals

my kz was sitting for about 10 years before I got to it and it seemes to run fine except it smokes a bit most noticibly on idle, I have heard the the valve seals go with age so I'm guessing thats it, how difficult are they to replace, and are they a major problem if it's run in this condition. or do they plump back up with use (its gone maybe 100 miles since I bought it)

also, the bike while it runs quite well, doesnt really seem to be able to really go faster than 80, however I can't say this for sure as I haven't really had a couple miles worth of open road to test it, but it sure feels like its giving its all at that point, am I just overestimating what it should be able to do, or does it just really need alot of space to wind out in top gear?

When it's all good, it should get near 100. I had one that went over 100 according to the speedometer, but I don't really know how fast that was.

There might be more in there but it'll take a fresh engine to see it, at least a top end. Once you see it, clean oil will maintain it!
KZCSI

just topped it off with some fresh oil, it had obviously sat for awhile with the fuel on as the oil i had originally was contaminated, the oil I just pulled out was real dirty, and I went with 15/30 to try and slow the smoke,and it seemed a little better, how would 20 wt go? would it drag the motor? to be honest, if its not gonna hurt the engine, it feels like im back on a 2 stroke:woohoo:

You'll find some good info here also.

www.kz400.com/

what size is it...550...650...750...etc....i had a 77 kz 650 bone stock that would hit the ton quite easily...now running a 78 ltd1000 that will see 100++ in third....