Bad Vacuum Advance?
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Bad Vacuum Advance?
In this video the engine is pulling 18lbs vacuum with the vacuum advance disconnected, when I connect the vacuum line to the vacuum advance and rev the engine the idle increases and vacuum jumps to around 22 until I disconnect the vacuum line and then it drops back to 18 and the idle drops to normal.
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Connected to the "vacuum tree" on the back of the manifold.
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
At idle spec the "ported" or spark advance connection should have no vacuum, thus no additional engine advance and timing is only the initial or crank advance set at the distributor.
Leaving the vac advance disconnected and plugged - the hose that is - the dizzy doesn't matter - as RPM increases, the mechanical advance should come in. Stay out of the plane of the fan blades in case they let go, but if you spool up the RPM to 3000 or more you should see all of the total mechanical advance - maybe 30 or 35 BTDC.
If you repeat the same with the vacuum advance connected you'll see an additional 10 deg BTDC or so, depending how much vac advance is set up.
Crank timing + Mechanical (weights/springs) + Vacuum Advance is typically about 45 or 50 deg BTDC at highway cruise. Or it used to be, when pump gas was good stuff.
Leaving the vac advance disconnected and plugged - the hose that is - the dizzy doesn't matter - as RPM increases, the mechanical advance should come in. Stay out of the plane of the fan blades in case they let go, but if you spool up the RPM to 3000 or more you should see all of the total mechanical advance - maybe 30 or 35 BTDC.
If you repeat the same with the vacuum advance connected you'll see an additional 10 deg BTDC or so, depending how much vac advance is set up.
Crank timing + Mechanical (weights/springs) + Vacuum Advance is typically about 45 or 50 deg BTDC at highway cruise. Or it used to be, when pump gas was good stuff.
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