As far as the "loping" effect you're having while idling, this is only tongue in cheeking it, while the engines running, I generally use carb cleaner with the straw installed in the spraying tip or you can use a rubber hose attached to a bottle of propane and either spray "sparingly" or "snoop" that hose around while giving some propane to any areas where there's gaskets and even around the carburetor. Any change in idle denotes a leak. Make sure you're not allowing any down through the throttle bore of the carb. Steer clear of any spark emitting cables and the distributor cap. As for the exhaust leak, use a mechanics stethoscope without the probe. Just the hose, then just move the hose and listen around for where your leaks coming from. You could also use this for any vacuum leaks. Just listen for any whistling of air being sucked into the leak area. Other than that, make sure of your fuel pressure and fuel delivery.