Unburnt fuel come out of muffler while saw is running

Try removeing the cover and screen from the muffler and clean them useing carb and choke cleaner to remove carbon build up. Be very sure they are dry before thet are installed because this cleaner is exremly flammable.
I would turn down carb adjustment screws till they are all the closed then open back up one full turn and fine tune frome there.Turn idle screw to where it will idle good just to the point that chain sarts to turn,then back off to where chain is stopped. Turn run screw up to where it will run at full R.P.M. Then back off in very small increments till it just starts to miss then reverse till it just starts to
run steady again it.Remove air filter and clean.If it is a foam filter it may be washed with dish soap and hot water.Rinse out and let dry off you can use low pressure air. I hope this helps you. Thank you.

There is a number of reasons why this can happen, running the saw on too rich a fuel oil mix, most modern two stroke oil is ok to run at 50-1, air filter blocked creating over fueling, clean the filter, carb mixture screws set too rich, re set the H screw on the carb, carb flooding due to needle leaking, service carb, ignition system fault, miss firing, replace plug, or ignition unit.
Always try the easy stuff first before fitting new parts.