How to Find Vacuum Leaks

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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 motor. See the wiki article: Manifold/Head vacuum leak, internal.

[edit] Propane method

  1. Get a soldering propane tank and valve attachment.
  2. Unscrew the end of it so 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.

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.
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