Keihin KS2 explained


First of all, this guide is not in any way perfect. Information is gathered from internet and by exploring Audi 80 motor codes PM and NE (they are more or less very same engine).

Also used in VW Jetta 2, HV motor, 1.85 liter, 90 hp CAT 020 5-speed manual
This carburetor more often placed on Audi 80 / 100.


Figure 1. Vacuum system.

Units inside Blue dotted circled are related to carburetor and rigidly fixed on it. They go around of the engine compartment. Looking direction of the vehicle is shown in blue symbol. Notice: This is from VW Jetta II which has transverse engine. Audi 80 has engine mounted longitudinal direction, which affects also carburetor direction 90 degrees (counter-clockwise in picture). Main vacuum intake is behind carburetor, not at drivers side.

  1. Carburetor. Approximate location of vacuum nozzles inside the carburetor: e, f, g – a first chamber in the end flap in its closed position; These outputs are below the flap when it opens, h – the second chamber below the valve (direct manifold vacuum), the n – just above throttle flap, for ported vacuum, can be used also for ignition distributor. No vacuum at idle.
  2. EGR Valve – The EGR valve opens at high rpm when the engine is warm and recirculates exhaust gases into the intake manifold. This improves mixture formation and reduces exhaust emissions. Audi 80 did not have this. How it reacts to the temperature I could not understand. On SAAB900, which earlier I had, did have electric sensor. Nothing similar is not found.
  3. The 3-way vacuum valve (Audi 80 part number is 026 906 283 H) is controlled by an electrical signal. It’s pipe k normally sticks down. Voltage is applied to it at low revs – then tubes j and k are interconnected, and i is stopped. When at higher rpm speed (mine is happening at 1950 rev / min), the control voltage is lost and the valve opens up communication between i and k, thus muffling tube j. See figure 11.
  4. The vacuum valve for brake servo: a – to the intake manifold, d – to the brake servo, b and c – point vacuum intake (the valve itself should not affect those). We need the valve because fall of vacuum affects directly air-boosted brakes. When valve is working correctly, there is some time to working brake boosting, even when the engine is stopped.
  5. Vacuum drive of the distributor of ignition. Shifts the ignition timing 0-20 degrees according to the vacuum in the intake pipe, ie, adjusts the ignition under the speed / engine load. Should be electronically controlled or connected to ported vacuum (f) (just above throttle flap), to keep idle timing advance correct.
  6. Vacuum actuator of gas throttle. Triggered when applying a vacuum to the vacuum pipe q. When the vacuum falls, valve immediately returns to its original position. Vacuum unit with the valve 7 is there to prevent sudden discharge of the gas throttle which could stall engine. If a vacuum is applied to the point r, a vacuum actuator is dispensed very slowly.
  7. One-way vacuum valve opens when the vacuum is fed to the right (on the picture) his side (white in real life). Serves vacuum actuator of gas throttle №13.
  8. air intake system.
  9. air flow switch (from the engine compartment – from the exhaust), operated by an actuator. Switch is for increasing the intake air temperature in cold weather. 
  10. A thermostatic valve controls the vacuum supply for number 9. (Audi 80 part number was 049 129 630 A). On the cold, connecs air intake atmosphere and m. On hot, connects both their pipes with air intake atmosphere. Vacuum system sucks air through a very delicate hole. Easy to check working with heat blower (cold motor running same time). See Figure 10.
  11. Delay nozzle – a narrow tube with an internal diameter of 0,4mm – a kind of air jet slowing dramatically the vacuum increase in the system. If you apply a vacuum at point p, vacuum actuator №6 work and the vacuum dropped from this point of the vacuum actuator №6 will be released very slowly. (Audi 80 part number 049129638)
  12. The vacuum tank.
  13. Vacuum unit fortifier for choke. When applying a vacuum to the outlet o (eg, through the mouth 🙂 slightly lifts the valve if choke fortifier is pulled (located in the cabin). If the vacuum drops at this point valve closes immediately. This system is needed in order to slightly lift the flap fortifier immediately after a cold start. 
  14. Stage II vacuum actuator for the second chamber of the carburettor. This opens second throttle flap when engine is heavily stressed and has high rpm. Needs definitely vacuum port n to work.
  15. Electric valve overrun. It has no relation to the vacuum system, and is shown here ”to the heap.”
  16. co% adjustment (see figure 5)
  17. idle adjustment  (see figure 5)

e: vacuum port ~5mm below primary gas flap. Gives vacuum always except at WOT

f: vacuum port ~2mm on top of primary gas flap. Gives vacuum at partial throttle position.

g: vacuum port ~1mm  on top of primary gas flap. Gives vacuum at partial throttle position, earlier than f. So-called ”ported vacuum” for ignition distributor vacuum advance.

n: vacuum port ~3cm on top of primary gas flap. Gives vacuum only in high RPM.

h: vacuum port ~5mm below secondary gas flap. Gives vacuum always except at WOT


An arrangement of vacuum system

The node numbers on these figures correspond to the signature Fig.1.
Right-left means that we stand against the vehicle speed and the engine is located across the (VW). vehicle travel direction is shown by a blue symbol

Figure 2. Top view of the right of the carburettor.

EGR valve №2 showing, cleverly hiding from the camera because of the hoses.


Figure 3 Top view of the right of the carburettor but closer to the cabin


Figure 4. View of the carburetor top left.


Figure 5. View of the carburetor shot from the right side. (Frontside in Audi 80)

Figure 6. View of the carburetor shot from the left side. From the point o the vacuum hose is disconnected. Screw t allegedly used to adjust the idle speed.

Figure 7. View of the carburetor removed from the front. (Driver side on Audi 80), pulldown actuator (14) removed.


Figure 8. View of the carburetor shot back
. Notice that Audi 80 model does not have f, g nor e (on right on picture) vacuum ports. Black tube that goes from the top, leaving a loop, is not a hose, but sable supplying power to the electric valve overrun №15.


Figure 9. Carburetor in VW Golf and Audi 80:


Figure 10: Intake air preheating vacuum switch


Figure 11: 3-way vacuum switch