Question for the 1st generation riders and wrenchers out there

I'm no stranger to bikes and I'm no stranger to my tools. I' just plain stumped on this one so give me what you got, please.

85 vf700f 28k miles, New tires and new chain and sprockets this month. 50 mph the bike sets up a vibration or undulation as if I'm going over expansion joints on the highway. It cycles about every second at 50 mph and get faster with with more speed. It becomes undetectable above 65. (tickets!) I'm guessing that the tires are working off of each other and getting this rhythm going and setting up this motion. The bars will wiggle back and forth if I let my arms go a bit floppy.

Should I be looking at steering head bearings? All of my wheel bearings are good and like I said, the drive train is new from the output shaft back.

Might my front springs be sloppy? WTF, man?

 

Did the bike do this before changing the tires?

Have you checked the torque setting on the steering stem nut?

 

As asked before, Did the bike do this before changing the tires? If not then it's tire balance most likely. If it did, then a bunch of things come to mind. First it sounds like two different problems. Tire vibration and bars wiggle. You didn't say what road surface was when this happens so assuming smooth average road.

Vibration: tire balance, check wheel bearings for roughness, alignment of rear wheel/sprocket so chain runs in alignment, possible rear shock or forks are not working correctly.

Wiggle: steering head bearings out of adjustment (loose), There is a specific procedure for correct setting. Possible slightly bent front rim or bogus tire.? Front forks need new fluid or level low. That's the way I would start in order.

You can check the balance of your tires yourself. Need two jack stands. Raise stands up (level) some so wheel axle can set on them with tire off floor. Use wheels axle and place on stands with tire in between. Lightly spin wheel and see where it stops. Do this multiple times. If it stop in about the same place, heavy spot will be at the bottom. Then wheel needs balance. If it stops in various places then it's balanced. Try these things and let us know if you find it.