|Adventures Under the Hood|
The Sol-Vac is an idle speed positioner that is a two-part vacuum and electric solenoid. The plunger opens the throttle a little to increase idle speed under certain conditions. The vacuum-operated portion increases the idle to 1100 rpm. The electric solenoid part holds the idle at 900 rpm. The computer determines which one and when.
If the engine is running okay otherwise, there is a simple test for proper Sol-Vac operation.
Warm the engine fully. Shut it off. Restart the engine. It should idle at 1100 rpm for 15 seconds, then drop to 900 rpm for 45 seconds, and finally drop to curb idle speed of 680 rpm (These numbers are for the manual transmission).
To test the vacuum portion of the Sol-Vac, run a vacuum hose from the nipple to a source of manifold vacuum. The plunger should pop out and raise the idle to 1100 rpm. Check for vacuum at the Sol-Vac vacuum hose during the first 15 seconds of engine operation. If there is none, check the vacuum solenoid on the valve cover for proper operation
To test the electric solenoid portion of the Sol-Vac, unplug the wire coming from it. Connect the wire coming out of the Sol-Vac to a jumper wire going to the positive battery post. The solenoid isn't powerful enough to push the throttle open, so manually open the throttle a bit and the solenoid should engage. Release the throttle and the solenoid should hold it open just a little, raising the idle to 900 rpm. Remove the jumper wire and the solenoid should disengage, dropping the idle back to normal. Check for 12 volts at the Sol-Vac harness connector during the first 1 minute of engine operation. If there is no voltage, check for an electrical problem between the Sol-Vac and the computer (including the idle relay). Make sure the Sol-Vac is grounded to the engine via the carburetor body.
(Be careful with the jumper wire: accidentally touching it to a ground, such as any part of the engine or car body, could result in damage or even an engine fire.)
Setting the idle with the Carter BBD is a four-stage process. The engine must be thoroughly warmed up to operating temperature and all electrical accessories must be turned off. Engine timing must be correctly set, and the Sol-Vac must be functioning.
Remove the jumper wire.