I have a meco saw that I purchased new in a 2003. They are very good saws and in some situations only the meco can handle rough terrain. Sometimes, depending on the model, it is not the saw that is causing you to cut crooked.
It could be the cutting method. Example: if you have the blade on the right hand side, and you make your first pass in the concrete too deep and/or push it too hard, it will pull to the right. Make your first pass 2" deep and don't use all your horsepower. Then go deeper on the second and third pass and so on, and add full power.
Also if you are turning the blade too fast, it will be out of its specified tension speed, it will NOT cut strait.
Use only the right hand side to cut unless you have to use the left. These saws are set up and are alligned to cut mainly on the right hand side.
If you need a manual, Husqvarna bought Meco a couple years ago (unfortunately). I think the web sight is
www.husqvarnacp.com .
Also, I have well over 2000 hours on my machine and have never adjusted the drive alignment.
What Model do you have? Mine is a 57HP Deutz Diesel with a 3 speed gear box. I love it. It is still the preferred saw in the shop over 3 Target (now husqvarna also) saws.