Salam.... firstly congratulations with your purchase...
secondly... the jamming that you have mentioned is directly effecting your rides average....
Do the following now or on your next tune.
Ask the mechanic to take out the front wheel and then apply grease or oil to the speedometer pulleys inside the hubs and also to the axle that is fitted in the center to make sure that it does not jam the wheels in its rotation. Also ask him to apply sand papers on both the drums and the brake shoes.
Also ask him to further decrease the front brake by rotating the adjustment screws till the wheels are free enough.
Now some people have habbit of riding the bic while their foot is pressing the rear brake pedal which actually on occasions also turns on the brake lights. This is fine if you are riding CD70 BUT if you are riding other brands like that of YAMAHA and SUZUKI then it applies the brakes to the wheels without you knowing about it. Check that this is not your case.
You can check it by touching the drums after a short or long run to see if they are unusually more hotter as compared to one another. Since front brakes are less used so the front drum should be less hot than the back drum.
I hope this helps. Best Regards and ALLAH hafiz for now.