take the flame nozzle off your propane torch and put a good length of vacuum line on the neck.. crack the valve about a half-turn... move the vacuum line over intake gaskets, etc., even other vacuum lines... rpms will change if you find a leak...
you could do the same thing with carb cleaner or brake cleaner, but you use a lot more of it and a stray spark will ignite it (been there, done that)
