Thread: Surging & coughing at very light throttle

The short answer is that your vacuum advance is moving the tip of the rotor button past the contact inside the distributor cap. If you inspect the rotor button tip you'll find that there is a burn mark at the corner of the brass strip instead of the whole working edge. I suspect the main reason is the alignment of the star rotor on the distributor shaft is out, not sure if there's much you can do about that. A simple cure is to use a rotor button with a wider tip. I've faced your problem often enough and so I've replaced the OEM style one with an XF Falcon one, Bosch part number GB864. It's a bit tighter on the shaft so make sure that you burnish the shaft end with some wet n dry before fitting the XF rotor button. It looks completely different but works quite well.

Another possibility is to use the arm off your old vacuum advance and use it to extend the arm on the new advance. A dob of weld to make it 5mm longer could fix all your problems.

Thankyou Bee Utey.
I ended up tying a knot in the vac advance hose and the damn car runs better than it ever has lol!!!!
I will inspect the rotor tomorrow and do as you suggest.

How weird. I had a few beers at a mates house and chatted about the problem.
Got him to drive the car vac advance off and on so he could see the problem.
Decide to go home and at that point i think... Hmmm it seems to get way to much advance so i will try retard it by restricting the hose.
Not sure why but its running like a beast now lol.

Replaced the rotor button with the Bosch GB864
No difference to my problem at all.
Actually almost feels a little worse now when i take off the advance.
Problem or surging and coughing still happening.

Check your distributor cap for carbon tracking, it may be damaged from going too far with the problem before you changed the rotor button.

I have only had the car about 9 months.
When i first got it the vac advance did work and work fine.
Some point recently it failed.
Because i had another issue i did change the coil and ignition module to the above.

I wonder if its infact the problem?
Is that ignition module supposed to give a longer duration of spark?
If so thats sort of what the problem here is right?
Excuse my ignorance as electrical is not my strong area.
Im considering actually changing back to the original ignition module to test if thats the problem.


Sure i could change the cap and leads plus buy a new dizzy but my wallet is starting to dislike the disco.

Im not even convinced its an ignition issue to be honest with you.
I have a MAF issue i cant seem to work out and i also ponder if that is the problem.
Damn cars!!

Ok had a couple of days off thinking about this problem.
Been doing my head in a little bit to be honest. Wasting money after money.
Anyway.........

I checked the star rotor in the dizzy. Turns out there IS some play there.
Additionally and im a touch embarrassed to say this but the pickup to the star rotor was loose!!!
Now in my defense i have never touched the pickup. Not that that is much of a defense.

Can the star rotor be glued or lock tightened to stop the play?
Would changing to the old ignition module hide the problem?
Going to tune it again today now i found the pickup issue and see if that was the underlying cause.

Is the vacuum advance actually engaged with its pin on the advance plate? Hint: apply vacuum, ie your mouth, to the vac hose and observe the advance plate, does it move a small bit? With the plastic cover off it should be easy to see if the vac advance capsule's arm is engaging its pin.

Is the star rotor actually loose on the shaft or is it just the movement of the advance mechanism? Hint: hold the shaft still while you wriggle the star rotor.

If the star rotor is truly loose on the shaft then remove the circlip, washer and O ring and put a drop or two of super glue in the gap. Hold the star fully clockwise against its slop as you do so.

Is the pickup actually loose or is it just clearance in the vacuum advance plate. Hint: check all visible screws for tightness.

Have you looked for carbon tracking in the cap yet? Hint: a strong light and perhaps some reading glasses or a magnifying glass will help you look for fine trails between the contacts.

Pics of a dissy fix are here.

Careful observation beats a panic attack every time. Fix the problems you see before inventing new ones.

Originally Posted by bee utey

Is the vacuum advance actually engaged with its pin on the advance plate? Hint: apply vacuum, ie your mouth, to the vac hose and observe the advance plate, does it move a small bit? With the plastic cover off it should be easy to see if the vac advance capsule's arm is engaging its pin.

Yes vacuum is connected properly. Tested with sucking and timing light.
Visually inspected also and can see plate moving as expected.

Originally Posted by bee utey

Is the star rotor actually loose on the shaft or is it just the movement of the advance mechanism? Hint: hold the shaft still while you wriggle the star rotor.

Yes the star rotor is loose. I can move that independently to the shaft.
Not a great deal of movement. A very small amount but it is visible.

Originally Posted by bee utey

If the star rotor is truly loose on the shaft then remove the circlip, washer and O ring and put a drop or two of super glue in the gap. Hold the star fully clockwise against its slop as you do so.

Ok i will give that a go as it seems a simple fix.

Originally Posted by bee utey

Is the pickup actually loose or is it just clearance in the vacuum advance plate. Hint: check all visible screws for tightness.

One of the nuts that hold it down was finger tight when i looked at it so yes it was loose.

Originally Posted by bee utey

Have you looked for carbon tracking in the cap yet? Hint: a strong light and perhaps some reading glasses or a magnifying glass will help you look for fine trails between the contacts.

I have yes. I cant see any but it is possible i just dont see it.
I have it outside and cant see any.
I am noticing a little burning on the outer edges of the contacts that i had not noticed previously.

Originally Posted by bee utey

Pics of a dissy fix are here.

Thankyou bookmarked for reference.

Originally Posted by bee utey

Careful observation beats a panic attack every time. Fix the problems you see before inventing new ones.

I decided to stop looking at the car for a few days.
Not sure that constitutes a panic attack.
As for fixing the ones i see. Well thats what im trying to do mate.
As for inventing new ones??????
Its a disco!!!!! If im not mistaken the car makes em on its own.

Thankyou for replying Bee Utey.