R/C CAR : General Question

I am a new user of fuel-powered cars and although I have adjusted the engine as per the instructions, it still won't start.

My MINI-Z series car doesn't always go smoothly in forward or reverse. Is there any adjustment that can be made to fix this?

My MINI-Z has been functioning perfectly up until now, but suddenly it won't go forward or reverse. How can I fix this myself?

Why does my MINI-Z series car suddenly turn left or right while I am driving?