Originally Posted by
pizzaguy
A really cool way to determine if a vacum leak exists: Pull the oil filler cap off. If the engine idle speed varies, the case is sealed well and you have no leak. If the engine idle speed is not effected, you have a vacum leak!
Smart idea
another way to find them is to use a short burst of starting fluid , but you need to leave the air cleaner on and the engine idling, if the rpm goes up then you have found your leak, if it has no reaction then you do not have a vacuum leak. Be very careful because ether is highly flammable, as long as you don't use it around a spark or open flame you'll be okay.