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Rochester Quadrajet Idling Issue

Since the day I got my Constantia (with Holden 308 and T350 box) it had this idling problem.

When it was cold it would not idle and when you engage any gear it died. When it was hot it idled but when you engage gear it jerked and it felt as if the torque converter did not disengage properly.

There are many web sites with advice on this idling issue of the 308 Holden engine, which are all relevant but none of those solved my problem. Common problems are:

  1. The air correction screws that is not adjusted properly. It might be part of the problem but air correction cannot make such a huge difference.
  2. Timing, timing does play a role yes.
  3. Kick back cable or solenoid - yes, it also played a minor role in my case. The kick back cable is too short, thus made a kink. So once it engaged once it did not release properly.
  4. Vacuum leak on manifold especially on pipe running to modulator. Yes this can cause a problem but more likely will cause a problem with gearing up.
  5. Metal vacuum tube from engine to modulator was replaced with a rubber tube. They say that because of heat the vacuum can suck the pipe so it collapses. This can be true if you use a thin rubber tube.
  6. Vacuum advance tube can be connected to wrong distribution point on inlet maifold - I connected mine directly from carb to distributor.

After many adjustments to timing, air correction, idling , etc I eventually investigated the idling cycle on the Rochester AGAIN.

I found that the port running from the opening marked below to the main jet was blocked. Thus fuel could not run from the float chamber to the idling port.

I opened it with carb cleaner and a very thin wire. The carb cleaner comes with a little pipe you put on the spray bottle. Put the other end over the port and hold it tight. The spray some carb cleaner into the port.

First try to open it by forcing carb cleaner in the channel. Keep your face away from the carb when doing this as it has the tendency to spit you in the face and you might end up with carb cleaner in your eyes.

If carb cleaner alone does not help use a very thin wire with car just to loosen the dirt.

Rochester idling issue

When you spray carb cleaner in the upper channel (as in above pic) , carb cleaner should come out the main jet on the same side. (see pic below)

If you spray carb cleaner into the bottom channel (as in above pic) it should come out in the throat of the carb just above the butterfly. That is the idle discharge channel.

This fixed all my problems from idling to getting it to engage gears without a bang.

The Rochester is not an easy carb to open and close. Take care, if you are not experienced let somebody with experience assist you.

308 Holden idle