Topic: Heavy vibrations from 50mph and riding

[PeWe]

A friend has a CB750A -77 (Japanese stickers) in mint condition but vibrates very much when he rides it.  He has tried to figure out what cause these vibrations.

Any CB750A specific that can cause heavy vibrations?

Bike vibrates a lot from around 50 mph and rising.
Problems holding the handle bar.
No specific noise at idle.
4 springs inside engine and converter replaced too. Same vibrations.

Experiences with solutions/ workarounds are welcome

[sammon287]

Wheel and tire balance, probably the front, seems like the obvious answer. Did it lose one or more balance weights? Does coasting make a difference?

[flatlander]

i was also thinking it might be a tyre. could be that it was installed unevenly. usually if you deflate it, roll it around a bit and then inflate it again, it will seat properly.
i'd try this first as it would be the easiest cause to find and fix.

[Stev-o]

i was also thinking it might be a tyre.

+1.  I bought a bike with an old front tire and it nearly bounced off the ground with that old, hardened tire on there.
New tire solved that issue.

[raymond10078]

With the bike on the centerstand - first in neutral - does the engine cause the vibration?  In gear - does the vibration appear now?  think wheel/tire balance and/or truing issues.  still nothing?  think front tire wheel issues.  weight the back end until the front wheel comes up - give it a spin, look for problems.

[PeWe]

Thanks guys for all things to verify.
Any specific that can happen Automatics?