L293D Problem- can't run both motors together
Apart from checking that your 9V battery is "man" enough for the job you are advised to consider how really poor the L293D is in your application: -

L293D H bridges don't realistically do what people expect them to do. That's not a problem of the chip - read the spec and you can see that at about 1A load the output voltage to be expected is a serious amount less than the power supply voltage. Here's a picture from another answer about the L293 and L293D on a 6 volt supply: -



If the supply voltage is 9V, with a 1 amp load expect the PNP (top) transistor to "lose" up to 1.8V and the NPN (bottom) transistor to lose up to 1.8V. This means, at 1A, the motor will only have 5.4V across its terminals and the L293D will be dissipating a power loss of 3.6 watts and shutting down.

Time after time questions come up about the L293D, the SN754410 (identical in all but name) and the L298 (it has a heatsink but is still inferior in every other respect).

Don't use them. Instead use a DRV8800. It uses FETs with an on-resistance of about 0.5 ohms meaning the top transistor will "lose" 0.5V at 1A and 0.4V the bottom transistor. That's less than a volt lost compared to the L293D which loses over 2.6V (typically).

Alternatively, use the DRV8837: -



Worst case on-resistance for BOTH top and bottom FETs is 0.33 ohm - in other words, from a 9V supply, with a 1A load, the motor will receive 8.7 volts and the chip will dissipate 300mW. Much more effective.