How do I get the stop screw loose/out that is used to adjust the choke valve (choke valve pulldown distance is supposed to be 13/64") so that I can hopefully get my choke to stop sticking. Now that it's cold it takes forever to get the engine warm enough to pull the choke off so consequently it runs too rich and rough for the first 5 minutes. I rebuilt the carb and it runs great otherwise but since that darn stop screw prevented me from making that adjustment the jobs not quite done. I tried PB Blaster on it with it sitting upside down but only succeeded it breaking one of the two sides of the slot (for the screwdriver). Anybody been there done that? Or other suggestions? Can I switch an air horn from another 2100 if I succeed in killing this one?