Check this 1st.
If your buggy is freewheeling and you don't want it to diagnose the problem in this manner. With engine off and car and radio on take off air filter. give it gas and then release look in the carb if when you release the throttle. Does the slide in the carb return to closed position should be aprox 1mm from completely closed in most carbs. If it does not hit the brakes see if that pushes the slide to the closed position. If it closes after hitting brakes then you need a throttle return spring. i.e. a couple rubberbands around carb and throttle pin should do the trick. The kind you wife or GF uses in there hair will work and are fuel proof. Also work wonders for keeping pressure on fuel tank lids.

If when you hit the brakes the carb only closes to 2mm's or more it's your idle screw turn counter clockwise to close gap. Of course clockwise to open gap. Slide should be held open when adjusting.

Now that you know your basic setup is fine check your radio trim. Adjust trim and watch linkage. Trim should be adjusted so when in neutral there is no servo load from either brakes or throttle. Carb should be closing automaically with addition of rubberbands. make sure your throttle linkage arm has enough length to be in neutral and still close carb. Without applying any load to brakes. Length can be adjusted through the turnbuckle at the end of the arm at servo horn.

Now that you have your second principal taken care of. Make lsn adjustment with car warmed up.