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--- engine:vacuumrouting [2026/05/18 19:30]
114.119.133.125 old revision restored (2025/07/23 12:04)
+++ engine:vacuumrouting [2026/05/20 09:52] (current)
47.128.38.234 old revision restored (2026/05/12 08:06)
@@ Line 5: / Line 5: @@
 The US cars had air pumps equipped for emissions compliance. Most owners removed this system due to the fact that it would frequently break. The diverter valve and the associated plumbing is usually removed. Additionally, although the vacuum diagram seems to indicate that there is a line coming off the vacuum pump, this doesn't appear to be the case for many cars.
-{{:engine:screen_shot_2021-12-22_at_8.49.00_pm.png?600|}}
+{{:engine:screen_shot_2021-12-21_at_9.38.54_pm.png?600|}}
-There are effectively two "circuits". One is the circuit that is always under vacuum (orange line). The other is the intake pressure circuit that may be at a vacuum, but can also be under pressure (acceleration with turbo pressure).
+As explained below, the two purple boxes are the vacuum solenoids for fuel pressure and ignition. When the solenoids are not energized, the yellow and green lines are connected (ignition), and the yellow and orange lines are connected (fuel). When the solenoids are energized the blue and green lines are connected (ignition) and the red and orange lines are connected (fuel).
+==== Vacuum Solenoids ====
-The ignition solenoid connects the distributor to vacuum when the car is started cold (with choke) which should advance the timing.
+There are a pair of solenoids mounted under the intake plenum for fuel pressure and ignition. Lotus refers to these as part #A910E6634F.
-The intake flap valve should be open under vacuum (when the car is running). When the engine is shut off, the vacuum should bleed out of the system through the air box and eventually close the flap valve.
+== Ignition ==
-The fuel pressure solenoid connects the fuel pressure regulator to the intake pressure circuit which will increase the fuel pressure under acceleration. The solenoid itself will force the fuel pressure regulator to drop pressure when the accelerator is not being pressed.
+Located beneath front of plenum chamber. Function is to advance ignition on operation of choke. A micro-switch operated by the dashboard end of the choke cable (which also operates the choke tell tale lamp) energises the ignition solenoid. The signal to the distributor vacuum advance capsule (normally connected to No.1 cylinder throttle
+edge drilling) is then switched to the vacuum pump, and thus full ignition advance is achieved, together with an increase in engine idle speed.
-The purple and green lines are simply "dump" lines (of a sort).
+== Fuel Pressure ==
+Located beneath rear of plenum chamber. Function is to reduce fuel pressure on 'overun' and idle. A micro-switch, mounted on the front of the front carburettor, and operated by the throttle lever in its fully closed position, energises the fuel pressure solenoid. The signal to the fuel pressure regulator (normally connected to boost pressure in the plenum chamber) is then switched to No.1 cylinder inlet manifold depression, thus reducing
+fuel pressure to the carburettors and mixture strength under closed throttle 'overun' conditions.
-==== Vacuum Solenoids ====
+== Replacement ==
-== Fuel Pressure & Ignition ==
-There are a pair of solenoids mounted under the intake plenum for fuel pressure and ignition. Lotus refers to these as part #A910E6634F.
 I took some time to test and investigate these solenoids (they are identical parts, but serve two different purposes).

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