I've suspected a vacuum leak on my Ranchero but could never find it using the spraying carb cleaner method. I'm looking forward to trying this smoke method. It sounds ingenious!Lift the lid off the carburetor and slip a baggie in there and then screw the lid back on. Find yourself a good hose to the intake, like PCV or emissions or power brakes. Light a cigar (recommend a Black & Mild wooden tip) and blow the smoke into that hose. Smoke will fill the manifold, see where the smoke comes out, there's your leak.