I like to spray around the carb base with starting fluid to check for leaks. Start the engine and let it warm up until it idles, and then just do short shots of starting fluid at direct spots near the base. Don't go crazy with larger spray shots, or a leak may suck it in where your overspray goes. If you have a vacuum leak the engine rpm's will jump up when it sucks the starting fluid in. Then you can see where the leak might be, and fix it. But don't stop with the first place you hear rpm's go up as need to be sure there aren't multiple leaks. And be careful not to spray too high where the filters might pull it in and give a false reading.