Your first step is to get a digital multimeter. Check the coil input voltages, they are always bad even in newish suzukis.
To increase the output voltage, you will imo need an entire kit, with a new coil and distributor, or at least ignition module.
It won't be a good investment, msd will probably cost more than the car.
The best you can do, check the battery voltage, it should always be atleast 14 volts. If not, you might have bad contact and grounding.
Second, you need to check the voltage at the coil positive with ignition switch in on position. It should be equal to battery voltage, else you should install a relay.
Next check the state of the ignition parts themselves.
I am sure your car will need the relay