First Bike - Scary weave problem above 60mph

Hi All,

New member, new rider (intro post here: kzrider.com/index.php?option=com_kunena&...=10&id=314484#314488 ) - and I need some advice regarding shocks on my 79 KZ650B.

Everything is alright up to about 60mph, but then she really starts to weave. I don't have many comparison points - just my buddies Yamaha Fazer 600, which feels rock solid at high-speeds - so, I know something's not quite right. It almost feels like you are hydroplaning - you don't feel in control of the bike. The bumpier the road, the worse it gets (and shakes the crap out of you) - so I'm thinking the shocks are not re-acting fast enough which in turn would cause the wheels to come up off the road for a much longer period of time than it should after hitting a bump. The tires are new-ish IRC Durotuours - so I don't think that's the issue. As mentioned, I'm a first time rider and not much of a mechanic so it's really just a guess.

I've checked:

Tire Pressure - Was low - setting to spec improved handling below 60

Chain - Loose out of spec. and dry. Set tension to spec and lubed. Bit nicer ride in general afterward.

Rear Wheel - No side-side play and is true (spoke wheels) - though there does seem to be a very slight wobble in the tread pattern...maybe 1/2 cm at the most...not sure if that could be an issue

Rear Swing-arm - No side-side play

Rear Shocks - Seem mushy.

Front shocks - Seem mushy.

I need to pick up a jack so that I can check if the front wheel is true and see if there is play in the forks.

My general plan at this point is to change the front fork oil, get some new progressive springs for the front forks, and change out the rear shocks completely.

Any advice on good front fork springs?

Any advice on good rear shocks? - I don't want to change out the swing-arm, but I'm open to getting some nicer modern rear shocks if anyone can point me in the direction of some that will fit.

www.progressivesuspension.com are good shocks.
I'd suggest the steering head bearings need replacement too.

Some other suspension places:
www.racetech.com
www.hygearsuspension.com
www.aftershocks-suspension.com
www.gpsuspension.com

Looks like you have checked most of the usual culprits, except one important one - the steering stem bearings. They can easily be checked as long as you have a centerstand. They can also be checked with a jack to raise the bike.
Put the bike on the center stand. Push down on the rear of the seat until the front wheel is an inch or two off the ground. Remove your hand from the seat. When the wheel hits the ground, if there is a light "clunk," the bearings are probably loose, and may need replacement.(Don't try this with the jack method.)
Push down on the back of the seat again. With the front wheel an inch or so off the ground, use your other hand to lightly and slowly turn the handlebars from one side to the other. If they immedieately flop to the side as you pass straignt ahead, the bearings are probably too loose. If while turning, you feel a light bump near straight ahead, the bearing may be hitting a dent in the race, which means that the bearings need to be replaced.
Loose bearings are pretty easy to adjust. Shot bearings can be a PITA to change.

New fork oil is a good idea as is replacing worn shocks and springs. Check with Z1 Enterprises or spring companies like Progressive and Sonic.
Dang, MFolks types faster that I do.

I have most of my info preloaded in folders, just highlight,copy and paste!

Thanks MFolks, TexasKZ - went out to my garage and ran through those checks. No clunk when I let the front fall a couple inches - but, the handle-bars did seem to quickly fall to the side on their own (a least to the left side...cables slowed the right side a bit). No bump near center - so I assume the race is not dented.

Also, I noticed that the stem base is not parallel with the bottom of the head pipe (thanks to the KZ650 owners manual with great diagrams I know what these things are called) - check out the picture...seems like these should be parallel...maybe something is bent? How does it look on your bike?

It's possible the previous owner dropped it,bending the steering stem/bearing races. Ask around and see if a bike shop will look at it for you.

The metal is kinda rough but mine appears level. The bottom tree does seem to curve slightly on our bikes though... Also along with above advice, have someone sit on rear of bike holding front wheel off ground. Now grab lower fork legs (move for and aft) and feel for any movement from bearings.