vacuum advance unit

[mrcosmos]

Hi everyone.Just a quick one.On the advance unit I have the usual vacuum pipe to the plenum which is fine.But its the other side.Only have about half inch of metal tube sticking out.Should this have a cover on it to stop air getting into the advance unit.Could you kind gents have a look at your dizzys and let me know[Griff 500 serpentine].Cheers,Dave.

Edited by mrcosmos on Sunday 18th March 15:23

[seasider]

On my Dizzy the rear ones covered, the one to the front is open with no pipe to the plenum, obviously the plenum hole needs to be sealed

Edited for clarity/Dave

Edited by seasider on Sunday 18th March 12:15

[spend]

I think he is talking about the vac advance on the dizzy. Not sure but I think mine just has a plastic cap/cover. If thats def what you are talking about I will have a look if neccessary.

Dave

ETA: Some chaps dont use the vac advance, & just remove the pipe + block up at the plenum end. Which is what the Sandman is referring to I think

Edited by spend on Sunday 18th March 13:33

[That Daddy]

Yes it should be capped,the rear one that is(nearest the cap)

[mrcosmos]

Hi,yes sorry.The plenum is fine.I meant at the dizzy[pipe to plenum is on the right of the advance unit and short metal tube on the left].Looks as though it should have a small cover on it to seal the hole.Cheers,Dave.

[GreenV8S]

Doesn't much matter either way, the cap just makes it look a bit neater and stops you worrying whether a pipe has fallen off every time you spot it.

[mrcosmos]

Cheers for that.Just thought it might affect the advance if air got in.Thanks,Dave.

[fastandcurious]

I've just spent the last 20 minutes hunting around for something to cap mine. Looks like I needn't have bothered! For a minute I thought that may be the cause of my fast tickover.

[that daddy]

No fastandfurious,the port to allow vacuum to the advance retard unit is only open when the butterfly is opened,so wont be the cause of your fast idle,but a vacuum/air leak maybe.

[GreenV8S]

I quick way to test for an air leak is to squash the air bypass hose flat. That should bring the revs down to the base idle speed of about 500 rpm (and it won't be at all happy idling that slowly). If you squash the hose flat and it still idles way above this then you need to track down where the air is coming from. If it's basically running OK them hopefully it is a metered air leak so you're looking at the base idle adjuster, throttle stop etc. Otherwise you're looking for a vacuum leak on one of the hoses to the plenum.

[seasider]

spend said:

ETA: Some chaps dont use the vac advance, & just remove the pipe + block up at the plenum end. Which is what the Sandman is referring to I think

Exactly But as everyone is saying the rear one is capped

Beach boy

[fastandcurious]

GreenV8S said:

I quick way to test for an air leak is to squash the air bypass hose flat. That should bring the revs down to the base idle speed of about 500 rpm (and it won't be at all happy idling that slowly). If you squash the hose flat and it still idles way above this then you need to track down where the air is coming from. If it's basically running OK them hopefully it is a metered air leak so you're looking at the base idle adjuster, throttle stop etc. Otherwise you're looking for a vacuum leak on one of the hoses to the plenum.

I did all this a few days ago, as mentioned on a little visited current thread marked "fast idle" Stepper motor new and clean. Base idle 2.5 turns out. 1100rpm idle.(rev counter a bit iffy) Squashed bypass hose and adjusted base idle to bring down to 500rpm. Still 1100rpm idle. The only way I can reduce this, is by winding the base idle screw in to the stop.

[GreenV8S]

fastandcurious said:

I did all this a few days ago, as mentioned on a little visited current thread marked "fast idle" Stepper motor new and clean. Base idle 2.5 turns out. 1100rpm idle.(rev counter a bit iffy) Squashed bypass hose and adjusted base idle to bring down to 500rpm. Still 1100rpm idle. The only way I can reduce this, is by winding the base idle screw in to the stop.

So base idle set correctly consistently gives you an idle that is a hundred rpm or so too high? Assuming the rev counter is reading accurately, that implies that the idle speed control is faulty. Is it working at all?

[Griffter]

Cap it with a short section of vacuuum tube blocked with silicon sealant.

[mrcosmos]

Cheers gents.Job done,hole capped.Thanks,Dave.