Look at the carb, there is a screw on the top of it that can limit the return of the butterfly. Make sure it isn't keeping the 'throttle slightly open whan the pedal is 'off'. This is probably what your friend "meant".
It's called an air-idle adjustment screw.
Most 2 cycle backfires (in reality are spit backs) caused by the combination of low engine RPM and the fact that the spark is set for operating RPM,(fixed). Add in a lean stumble through when opening the throttle (no accelerator pump) the engine pre fires and forces a pre detonation back through the crankcase and out the carb.Lean caused by (altered or faulty air box) (miss adjusted idle screw)(partly clogged idle jets, airways)(low fuel level in carb). On going spit backs are hard on the reed valves.
Make some adjustments on the screw - the throttle is being left open. Check both cables for proper adjustment and that they allow the carb to close all the way.
I have seen a million times - the idle screw on the carb turned all the way in, so that the throttle can't close all the way. People do this thinking it will increase the speed of the cart.
Clean the carb well, and inspect for any worn/damaged parts.