here’s a description how to setup external midiclock syncing for your Yamaha S90XS.
In the Quick Setup menu, you can choose setup 2.

This results in the following settings :
Local control: on
MIDI: auto
Clock Out: off
Arp MIDI Out Sw: all on
Perfect for synchronizing to midiclock .

The SU200 can be synced to midi clock by following the procedure described below :
1. Switch off all pads, and then press the [JOB] button to enter Job mode.
2. Press the [MIDI] button (pad 8 ) to enter MIDI Setup mode.
3. Set the MIDI clock (‘Sync’ on de the display) to ‘Ext’ :

4. Press [...]

The sophisticated sync features of the DX200 let you lock it in step with the rhythm of just about any other MIDI device, such as a computer, rhythm machine or external sequencer. No drift, no glitching, no slipping out of sync — the two machines stay perfectly in the same groove.
This is great for live [...]

On the Motif Rack XS you configure syncing to midi clock in the following menu :

Select midi (nr2).
Then Edit the MIDI Sync Parameter. Possible values are :
internal : Synchronization to internal clock. You can use this setting when this tone generator is to be used alone or as the master clock source for other equipment.
external [...]

The RS7000 Music Production Studio is quite advanced.

It can be synced to midiclock the following way :
In midi setup (page 1/2)

you can set the midi sync setting to “MIDI”
This way your RS7000 can be synced to an external
midi clock signal.

The Boss DR-3 can be synced to midiclock :
In the system menu, set the Sync parameter to auto :

The DR-3 will now sync to midiclock as soon as it has received the start command (which midiclock sends automatically when you press start).

Yamaha’s RY20 is a cool device.

Put the RY20 in MIDI Mode by pressing the [ MIDI ] button.
The “MIDI” indicator is now switched on.
The current mode is flashing below the “SYNC” prompt :
Switch from “INT” (internal clock, the default) to “MIDI” (external MIDI controller) by rotating the Jog Dial or by using the [ +1 [...]

TheRoland VG-99 and VB-99 can easily be synced to midi.
In the menu system/midi you can select the ’sync clock’ options :

The following settings are possible :
INTERNAL : the VG-99/VB-99 ignores any incoming midi clock commands : don’t use this setting if you want to synchronize with midiclock.
AUTO (USB) : The VG-99/VB-99 is automatically synchronized to [...]

Yamaha’s QY70 supports reception of midi clock signal.
You can edit the MIDI SYNC setting in the utility-midi menu :

When the MIDI SYNC parameter is set to “Internal” the QY70 is controlled by its own internal clock.
However, when set to “External” the QY70 is controlled by a MIDI clock signal received from
an external device such as [...]

Even the small DB-90 dr beat can be synced to midiclock. (see picture below)

To achieve synchronization, press the MIDI button on your db-90.
Your Dr Beat will switch to “MIDI reception enabled” mode.
The DB-90 now syncs to your midiclock and also follows the start/stop commands.
If you press the MIDI button again, the MIDI mode is cancelled, [...]