Carb vacuum port ID
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===Holley carbs=== | ===Holley carbs=== | ||
Many Holley 4150/4160 carbs will have a ported vacuum port on the side of the metering block. The other vacuum ports will usually be manifold vacuum. | Many Holley 4150/4160 carbs will have a ported vacuum port on the side of the metering block. The other vacuum ports will usually be manifold vacuum. | ||
| + | |||
| + | ==Chart of diagnostic vacuum readings== | ||
| + | <table> | ||
| + | <tr bgcolor="white"> | ||
| + | <td colspan="3"> </td> | ||
| + | </tr> | ||
| + | <tr bgcolor="lightgrey"> | ||
| + | <th width="26%">Engine Speed</th> | ||
| + | <th width="28%">Reading</th> | ||
| + | <th width="46%">Indication of Engine Condition</th> | ||
| + | </tr> | ||
| + | <tr bgcolor="white"> | ||
| + | <td width="26%">Smooth and steady idle<br> (800 to 1200 RPM)</td> | ||
| + | <td width="28%">Between 17 to 21 inches</td> | ||
| + | <td width="46%">Engine is in Good Condition, but perform next test to be sure.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Open and close throttle quickly</td> | ||
| + | <td width="28%">Jumps from 2 to about 25 inches</td> | ||
| + | <td width="46%">Engine is in Good Condition.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Smooth and steady idle</td> | ||
| + | <td width="28%">Steady, but lower than normal reading</td> | ||
| + | <td width="46%">Worn rings, but perform next test to be sure.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Open and close throttle quickly</td> | ||
| + | <td width="28%">Jumps from 0 to 22 inches</td> | ||
| + | <td width="46%">Confirms worn rings.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Intermittent dropping back 3 or 5 divisions and returns to normal</td> | ||
| + | <td width="46%">Sticky Valves. If injection of penetrating oil into intake manifold temporarily stops pointer from dropping back, it's certain the valves are sticking.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Steady 3000 RPM</td> | ||
| + | <td width="28%">Pointer fluctuates rapidly, faster engine speed causes more pointer swing</td> | ||
| + | <td width="46%">Weak valve springs.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Fast fluctuation between 14 to 19 points</td> | ||
| + | <td width="46%">Worn intake valve stem guides. Excessive pointer vibration at all speeds indicates a leaky head gasket.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Constant drop</td> | ||
| + | <td width="46%">Burnt valve or insufficient tappet clearance holding valve partly open or a spark plug occasionally miss firing.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Steady 8 to 14 inches</td> | ||
| + | <td width="46%">Incorrect valve timing. It must also be remembered that vacuum leaks and/or poor compression can result in a low vacuum reading.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Steady 14 to 16 inches</td> | ||
| + | <td width="46%">Incorrect ignition timing.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Drifting from 14 to 16 inches</td> | ||
| + | <td width="46%">Plug gaps too close or points not synchronized..</td> | ||
| + | </table> | ||
| + | <br><br><br> | ||
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