Editing Finding vacuum leaks

{{youcanedit}}
==Initial Diagnosis==
If you suspect a vacuum leak you may be able to verify your suspicion by performing a simple check.  With the air cleaner removed (carbureted engine) and the engine at idle speed, place a wadded-up rag over the carburetor throat to choke off the air supply.  If the engine rpm speeds up, chances are you have a vacuum leak.

There are several methods for locating vacuum leaks. Occasionally, you may experience a vacuum leak into the intake ports from the crankcase of the motor due to the intake manifold/cylinder head interface not being machined parallel. No amount of propane or carburetor cleaner will find such a leak. The best way is to insure the elimination of such a problem while building the engine. See [[Manifold/Head vacuum leak, internal]].

==Propane method==
#Get a soldering propane tank and valve attachment.
#Unscrew the end of it so that you have a threaded pipe without the nozzle.
#Attach a 2-foot piece of hose to the end.
#Start the engine and let it warm up a bit.
#Turn on the propane and run the hose all around the vacuum lines and the bottom of the carb.
#If the engine smooths out or revs up a bit, you have found your leak.

Hold bottle UPRIGHT during testing as liquid propane may run out of an inverted bottle.

PLEASE do this in a well ventilated area due to propane gas and exhaust fumes!

==Carburetor cleaner method==
#With the car running, using a can of carburetor cleaner spray down the hoses and vacuum connections.
#Notice a change in the running of the engine and you might have found your leak.

===Note===
You may also use engine startup fluid instead, as it is not caustic like carb cleaner, and does not leave residue.


==Vacuum gauge method (internal)==   

If the above methods fail to locate an external leak, the following procedure may be used to determine an internal leak.
#Disconnect/remove the primary wire between the coil and distributor.
#Adjust the idle screw so the throttle plate in the carburetor is completly closed.
#Remove PCV, breathers, and all vacuum ports on carburetor/manifold and seal openings with plugs/tape.
#Connect vacuum gauge to a manifold vacuum source.
#Have assistant crank engine while you read vacuum.
If gauge reading is 0-2", chances are you have an internal leak between the manifold/head.

[[Category:Engine]]