I made on with a 1 gallon jug, a fish pump and a cigar. Cost $.50 to make, those little cigars stink!! Air in the bottom, goes thru the cigar, makes smoke and the rubber tube from the top delivers it to the intake. Ram a rag in the intake after the air cleaner and the same into the exhaust. Smoke will come out at the leaks. We only used 1 cigar from a box of 3.
Works a treat!!! Found our vac leak. Lots of youtube vids on the subject.