I believe if you google the Zama website there is a wealth of information there.
On most carbs, you turn the hi and low screws in all the way and gently bottom them, then turn it out 1 to 1 1/2 turns. That should get it running and you can fine tune from there. There may be "limiters" on the carb screws installed as the EPA's way of limiting your ability to adjust the carb. You can cut those off to allow you to turn the screws, or sometimes screw a drywall screw down on them to remove them. You might also need a special screwdriver to fit the screw heads - these can be found on Amazon - called pac Man, single D, Double D or splined carb adjustment tools. Otherwise, cut a slot in the screw and use a flat screwdriver.
If the hi and lo adjustment doesn't fix the problem, you may need a rebuild kit. Take the carb off, look on the side for the number and use that to look up which carb you need. Even the same model of machine can use different carbs, so just knowing the model of trimmer may not be enough. Once you know which carb it is, you can order the rebuild kit, but you should also check to see how much a new carb costs. Sometimes it isn't much more than the kit.
If you get the kit, you need to totally disassemble the carb and gently spray carb cleaner through all the holes, then reassemble it with the new parts from the kit. If you happen to have an ultrasonic cleaner, running the disassembled acrb thru that is a great way to clean it. Ereplacement parts has a good video on how to rebuild carbs. There are also some small metal covers called Welch plugs that you should seal with fingernail polish or Indian head shellac. It these leak it can make the machine run erratically.
It is a good idea to check the fuel lines/filter while you are at it, especially if you find crap in your carb. Fuel lines should be replaced with something like Tygon, which is resistant to ethanol fuel.
Good luck.
