I'm having an issue where my engine (350) doesn't want to idle after about 30-40 mins of driving. When I come to a stop after about 30 mins of driving the car will idle normally at around 900 rpm for close to a minute but then the idle drops and the engine begins to stumble. If I crank up the idle screw it solves the issue but the car will idle way too high. Car runs and idles flawlessly for the first 30 minutes or so. I'm thinking this has to be a carburetor issue (Holley 650 recently rebuilt). Any ideas or recommendations?