I did a quick check for leaks (not as thorough as I’d like since I was short on time last week),
A "quick check for leaks" needs some fleshing out to become a useful description.
What is the production year of your Brick?, How long have you owned it? How much have you ridden it? What is the mileage on the odometer? How well was the engine running before you undertook this test? Was the exhaust pipe for cylinder #4 cooler than those of the other cylinders after idle? Do you know when the last time the valve clearances were adjusted?
If there is spark at all plugs, before I did anything else I'd warm up the engine, shut it off, then do a compression test of each cylinder with the throttle wide open.
If compression were okay, I would connect the Carbtune, start the engine, let it idle, go to the air balance screw of the throttle body #4, note the position of the air balance screw of throttle body #4, open and close—not completely—the air balance screw during idle to see if that had an effect then return the screw to its original position. If no effect, I would start the engine, let it idle, take a propane or Mapp torch and train a narrow stream of unlit gas around each rubber bushing and manifold connected to the air box to each throttle body, and listen for a change in the idle. A change would indicate a leak.
