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Rochester Varajet II

This was not the most popular carb choice that Holden ever made, at least not with many mechanics. It is fitted to the Camira, Holden4 star-fire engine and Holden6 Blue engine.

Common faults with these were:

  • Primary and secondary throttle shaft wear, causing idle instabilities
  • The metering rod popping out of the step-up piston (22), causing poor fuel economy & sluggish performance
  • The anti run-on solenoid (23) would fail causing the engine not to idle,
  • Blockage of the vacuum passage to the step-up piston & metering rod (22), causing high fuel consumption, and
  • incorrect idle & mixture adjustments (not really a carby fault)

According to the manufacturer, once the throttle shafts are worn, the base needs to be replaced, however these shafts can be purchased aftermarket in oversize and replaced by an experienced carb re-builder. Replacing the secondary shaft required grinding the connecting linkage from the shaft and then silver soldering the fitting onto the new shaft. If this job is not done with the utmost precision with the shafts and discs positioned correctly in the bores, the carb will be unstable at idle.

Anti run-on solenoid. (23) Its function is to ensure the engine stops when turned off at the ignition key. On late model vehicles with higher idle speeds this item is required, otherwise the engine may kick over with pre-ignition for a little bit after switch off. There are two types of anti run-on solenoids.

  1. fuel cut off - the solenoid cuts off fuel supply to the idle circuit.
  2. air by-pass cut-off - the solenoid cuts the bypass air around the primary throttle butterfly.

If a very thick compressible base gasket is used under these carbs, DO NOT over tighten the base nuts as this will result in cracking the carby base, but generally a bakerlite plate is used with thin gaskets on either side.

The primary & secondary disc position, the idle by-pass adjustment and mixture screw must all be adjusted exactly to manufacturers specs for this carby to perform at its best. Unfortunately in most cases the first thing to get incorrectly adjusted is the low speed screw which changes the throttle disc position in the bore and this has a roll on effect with the other adjustments.

There are various other linkage adjustments that need to be checked and corrected. It is best to get the specific workshop manual for your vehicle to accomplish this. If the throttle shafts have lateral movement then have them replaced.

All that said though, I can say that this carb when operating correctly will outperform a weber conversion easily, mainly because this carb is a spreadbore and has the best of both worlds, in reasonable economy and good power on the second stage. The big negative is that as far as I know there are no jets & metering rods available for performance tuning, so any mixture adjustments required on cruise and power need to be done manually and would be very time consuming. So it was just easier to throw a Weber / Holley on instead. 

2

float chamber gasket

14

idle air bypass screw & 'O' ring

22

step-up piston & metering rod

3

accelerator pump cup

15

choke shaft

23

anti run-on solenoid

4

pump discharge check ball

16

choke disc

24

accelerator pump link

5

needle

17

accelerator pump rod

25

fuel idle mixture screw

6

seat

18

needle & seat baffle

27

choke fast idle cam

7

pump inlet check ball

19

float retaining pin

29

filter

8

throttle body gasket

20

float

30

inlet fuel union

10

idle mixture screw 'O' ring

21

retainer for discharge check ball

 

 

Vacuum passage shown can block all the way to the step-up piston chamber. Be sure to check it is clear all the way. In this carb the solenoid (23) is an air by-pass shut-off. The air is drawn in from the venturi area and allows to bypass the throttle disc. The idle by-pass screw is the correct idle speed adjustment method used to adjust idle speed, not the low speed screw that contacts the primary throttle shaft. This screw controls the amount of air bypassing the throttle disc and therefore controls the idle speed. The idle mixture screw is usually sealed at factory but it can be adjusted to give a better idle quality. However be careful because it may cost you a little economy. These engines are specifically tuned lean, not for best vacuum or idle quality.

To adjust the float, press against the float retaining pin leaving the baffle off (18). At the same time press lightly against the float lever arm until the float seats the needle & seat. Measure from the top of the bowl to the top of the float. Measurement is 8.0mm. Be careful in bending the float to achieve the correct measurement. Do not put force on the float itself.