common causes of rough idle?

just had my wagon (72 type 3 1600 twin carb) fully serviced about a month ago, has been running like a dream since, but a couple of weeks ago i noticed a bit of a rough idle. she has been pulling beautifully and operating perectly whenever moving, but i have noticed that when at idle every few cycles she labours a bit on 1-2 cylinders, so the revvs drop slightly, the car vibrates slightly more on the stroke that the revvs slow, then it picks up again, this cycle can happen upto 2 times per second. initially i assumed maybe one of the sparkplugs had fouled (as i didnt get them replaced - they had only been done at christmas) so i put in some nice new plugs but that doesnt seem to have helped. i also know that the pervious owner told me the carbs were due for a rebuild when i bought the car (8 months ago) and i noticed when looking at the choke, that when the choke is on the upper butterfly in one carb doesnt moove the same as the other. as i said at full song there isnt a problem, she is as sweet as ever, just at idle that i get concerned.
what are the common causes of a uneven idle? should i be concerned?

one carb may be running a little richer ,or your leads may be braking down,

The twin carbs on type 3s are different...
I thought I read where even the jets can be different...
but they should be tuned the same.... at idle...

Check the engine at night....
I had a type 3 many years ago and i checked the engine at night and the spark plug leads were shorting out everywhere.... its a wonder it went at all...

You could check the mixture on both carbs,,,
You can do that by ear...
although a Tacho is handy...

also wipe out the distributor cap and rotor with petrol or wd40 etc...

best of Luck

Lee

http://community.webshots.com/user/vw68autobug

One of my cars was doing that last week.... lopey idle and a sometimes misfire at cruise. It was plugs (new ones fixed it - no other changes) but old/dodgy leads will do it too

Good tip from 68Auto about checking it at night... turn the garage lights off and see the fireworks!

I think you will find its a vacuum leak on the balance lines that run between the carbies, the later carbies have plastic Tee pieces and they crack easy

get a bit of clear plastic tube and stick one end in yr ear and use the other end around the carby and vacuum lines to listen for the leak

I had the same thing happen to me. Low uneven idle but fine when driving...it was the balance tube as vw54 suggests. One side had slipped off.

thanks 54, forgotten about the balance tube, i remember it was a nightmare when oen came off completely (sounded like 1 was running on 3 cylinders) but i know one side likes to slip around a bit, maybe its just sitting on again. that would explain today, got in the car and she purred all the way home with no problems at all. any good tricks for keeping those little bits of rubber in place? tiny hose clips?
cheers guys

youll find the hose will expand a little with age ,if its rubber you could just cut about an inch off and it should be harder to put on and tighter

Vacum hose is a goody but a nother easy one to over look is valve clearance this also effects idle

:beer