Steering wobble

[jonaf]

When I close the throttle, the handlebars wobble at certain speeds. My bike is an XS650B, 1975.
The wheels are in line. The steering head bearings are OK. The swinging arm bearings are new. The wheel bearings are OK. The tyres look OK. Anybody with the same experience?

 

[fredintoon]

Hi jonaf,
your steering head bearings may well be OK (clean, lubricated, no notchy feel when moved?) but are they adjusted correctly?
Here's how:-
Bike on centre stand, frame jacked up so the front wheel is clear of the ground.
Tighten the head bearings until the bars will stay pointed straight ahead but will fall to the side when given a gentle push to start them moving.

 

[gggGary]

Look carefully for cupping on tires.

Cupping will set up an easily damped oscillation at about 28-32 MPH depending on tire brand, model.

Define OK on those steering head bearings?

 

[5twins]

So many things can cause this. It could be any of the things you mentioned (even though you think they're good) or a combo of several things. Some other things to check would be tire pressures, tire match (are they a matched set from the same maker?), rear shocks (too stiff can cause a front end wobble). If the forks have never been serviced or not in some time, you might need some fresh oil in there. Maybe the springs are bad too.

 

[mrtwowheel]

Watch this video,

at 4:40 they show the inherent reason for slow speed wobble built into the geometry of motorcycle front ends, I call it "the castor effect". Yeah, you should check your wheel bearings, chassis bearings and tire conditions, but don't chase this problem with money when there may not even be a problem. At 165 pounds I can make any motorcycle, in any condition produce a low speed wobble. Tire cupping is normal wear, get your mileage from them. Keep your hands on the bars. Oh, gaining 50 pounds will also result in less low speed wobble.

Scott

 

[XSLeo]

How old are the tires? Do you know how to tell how old the tires are?
On the side wall is a number, it starts with DOT, has some numbers then at the end is an oval. The numbers in this oval is the date the tire was made.
If the oval has just three numbers they are very old tires. As in made before 2000. The first two numbers are the week of the year, the last two are the year they were made.
Like 2703. This is the 27th week of 2003.
Old tires get hard, they have the plies start to separate, the tread can separate from the carcass. None are a good thing.
The 81 when I got it had a wobble so bad at about 35 mph it about threw you off the bike. The old tire still had the mold nipples on the tread, looked like new. The plies had started to separate.
New tire no wobble.
If you read to date on the tires and find them over 6 years old, get new ones.
Leo