Finding vacuum leaks

From Crankshaft Coalition Wiki

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.

[edit] Propane method

1. Get a soldering propane tank and valve attachment.
2. Unscrew the end of it so that you have a threaded pipe without the nozzle.
3. Attach a 2-foot piece of hose to the end.
4. Start the engine and let it warm up a bit.
5. Turn on the propane and run the hose all around the vacuum lines and the bottom of the carb.
6. 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!

[edit] Carburetor cleaner method

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

[edit] Note

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