\"floating 400\"

my friend has a '75(i think) kz400 and when ive ridden it, it feels a little scary at times. i notice that it feels almost as though the swing arm is attached to a swivel or something. its very hard to describe. when coasting to a light sometimes it even feels as though you have to switch your weight around to keep it up right. going into turns it feels the same way, like it has a strange pivot to it in the rear. at least i think its the rear. he says hes never felt it but i feel it every time i ride it. he said that hes had the rear off the ground and the swing arm is solid but it sure doesnt feel like it when im on it. if anyone has any idea what im talking about please respond.

Hmmm.

Not a lot of hard details to go by there.

Given the symptoms, I'd take a long, hard look at the swingarm bushings and rear axle assembly regardless of your friend's opinion of the swingarm. :huh:

The other likely possibility is the neck bearings. If they're "original", what's left of them might be about enough to fill a shot glass. :whistle:

Either way, I'd take it easy on that bird until you figure out where the problem is.

Might be as simple as low pressure in the rear tire. Maybe the front too.
Another reason might be a mis-aligned rear tire. When you tighten the chain, you have to move the rear wheel, and it can get crooked. Don't use the little hash marks on the rear frame, they're not accurate. You should measure the distance to the adjusting bracket on each side.
Once it's straight, then adjust the chain tension by making quarter-turn increments of the adjusting bolt, on both sides. Make sure you tighening in the right direction on BOTH sides (don't ask).

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Check the air pressure. A bike tire might look fine, but the stiff sidewalls conceal low pressure.

Put the bike on the center stand. Disconnect the rear shocks at the swingarm and lift the wheel clear of the ground, then try to push it sideways back and forth. Any play in either the swingarm or wheel at the axle is an indication of trouble.

Reconnect the shocks. While someone is sitting on the back of the seat to get the front wheel off the ground, grab the forks at the axle and try to pull and push the fork to ascertain play. Again, there shouldn't be any.

Even if you don't find any obvioous problems, it is time to replace 32 year-old axle bearings. Lubrication in them is probably non-existant by now.