Finding vacuum leaks
(added quick vacuum leak check and method for detecting internal vacuum leak) |
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==Initial Diagnosis== | ==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 | + | 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]]. | 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]]. | ||
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===Note=== | ===Note=== | ||
You may also use engine startup fluid instead, as it is not caustic like carb cleaner, and does not leave residue. | You may also use engine startup fluid instead, as it is not caustic like carb cleaner, and does not leave residue. | ||
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| + | ==Vacuum gauge method (internal)== | ||
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| + | 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 PVC, 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]] | [[Category:Engine]] | ||
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