You really can't adjust it unless you have the transmission separate from the engine and you can get to the clutch.
The clutch in the Miata is Hydraulic so if you having problems with you clutch most likely the problem is the master cylinder, slave cylinder, or you clutch is bad.
Correction 10/26/09:
The above is partly incorrect. While it is a hydraulic clutch, there is a mechanical adjustment at the clutch pedal itself, which allows you to adjust pedal height and freeplay. Contorting yourself to look up under the dash to see near the top of the pedal, you can see the stop/switch that prevents the pedal from rising any further from the floorboard. That can be adjusted by disconnecting the wires, loosening the locknut, and turning the stop/switch to the desired pedal height. Freeplay (the amount of pedal movement before feeling clutch resistance) is adjusted by loosening the locknut on the rod connected to the clutch pedal and going into the firewall. Turning the rod one way or the other will increase or decrease freeplay. If you are adjusting both, always adjust pedal height before freeplay, as pedal height affects freeplay.
Now, clutches in Miatas rarely require adjustment, and most cases where one seeks to solve a clutch that isn't fully disengaging, will find that the slave cylinder (on the transmission bell housing) is going bad. (common at 100K miles) The good news is it's fairly easy to replace. You just have to be careful to properly torque the mounting bolts. (easy to strip the aluminum threads, as it only requires 12 to 16 ft.lbs)
Yes, all miata's have a hydraulic clutch.
Yes there is a hydraulic clutch on the miata. Just to the outside of the firewall, near the brake master cylinder is the clutch master cylinder and resevoir.
I used this guide when I changed the clutch in my 97. http://www.miata.net/garage/clutch2.html
No pressure in clutch resevior, its next to the brake resevior, if its empty, put more, if not you have a leak.
To replace the clutch on a 1991 Mazda Miata, first, disconnect the battery and lift the car securely. Remove the transmission by detaching the driveshaft, shift linkage, and bellhousing bolts. Once the transmission is out, you can access the clutch assembly; replace the clutch disc, pressure plate, and throw-out bearing. Reassemble by reversing the disassembly steps, ensuring all connections are secure before testing the new clutch.
Pictorial guide: http://www.miata.net/garage/clutch2.html
Isnt one, its hydraulic, and its next to the brake fluid resevior
Under the dash, just above the brake and clutch pedals to the left.
Should be next to the brake fluid cup. DJ FLIP Housepartykings.com
On a 1999 Mazda Miata, the clutch slave cylinder is located on the transmission, mounted to the bell housing. It is typically found on the driver's side of the vehicle, towards the rear of the engine compartment. To access it, you may need to raise the vehicle and remove any necessary components for better visibility.
To realign the shift linkage on your 1993 Mazda Miata, first, ensure the vehicle is securely lifted and supported. Locate the shift linkage under the car; you may need to remove some components for better access. You'll find a threaded adjustment on the linkage; loosen the lock nut and adjust the linkage to find the correct alignment, ensuring it smoothly engages all gears. Finally, tighten the lock nut and test the shifting to confirm the adjustment is effective.
To replace the clutch slave cylinder on a 1991 Mazda Miata, start by safely lifting the vehicle and removing the driver's side wheel for better access. Disconnect the hydraulic line from the old slave cylinder and remove the two mounting bolts securing it to the transmission. Install the new slave cylinder, ensuring it is properly aligned, then reconnect the hydraulic line and bleed the clutch system to remove any air. Finally, reassemble the wheel and lower the vehicle before testing the clutch operation.