Vacuum Advance not holding pressure - broken?

[sjmtlewy]

I'm trying to test my vacuum advance, because its old and a bit rusty, and am not entirely sure its working... I attach a bit of vacuum hose to the advance (round thing on the distributor - right?) and suck on the other end. Theres quite a bit of resistance when you suck, but it doesnt keep it at all. Does this mean its broken? Can I replace it without moving the dizzy, as I dont have a timing lamp etc?

Also, what effect is this likely having? Its got very little top end power and doesnt really go over 60mph, but I just thought that was normal.

[sarran1955]

Hello,

If you suck on your little hose, (no comments), you should see the plate holding the points move a good half centimeter to the left, and then return when the suction is released. If it moves back under suction it is probably a leaky hose. If you can get a timing light, paint a white mark on the timing notch on the pulley with tippex and connect the light as per the instructions. I use a Gunsons inductive strobe.

Make sure all the wires are free of all whirly bits and get you faithful henchperson to start the engine and let it tick over. In the flashing light you will see the painted notch hovering at about 11.30 o'clock. If you then rev the engine the notch will move to the left to say 10 o'clock and then return to its original position.

No technical stuff.

If you have conventional ,(not electronic )ignition you may want to clean and reset the points, and change the condenser.

To get the best setting, It's best to use a dwell meter, but that gets a little bit more technical

Basically, it's a VW, if it starts and runs ok then there's not much wrong.

Cordialement

[sjmtlewy]

The rotor arm doesnt move when sucking, is that what you meant?

But with the engine started, if I pull the vacuum hose out of the advance the idle speed drops noticeably

[sjmtlewy]

Actually, just had another look. If I suck really hard, the metal disc under the arm moves a tiny bit and then back again. But theres no way I can make it hold its position and it wont hold the pressure so that I can gradually move it.

Definitely not the hose, its a brand new unused length I'm using that holds pressure fine when you put your finger over the end.

[sarran1955]

Well if it moves then there isn't too much wrong,

However, if the distributor is circa 1982 AD, then it could well do with a clean out. scratch a line on the body of the distributor just above the locking clamp, and continue it to the crankcase. This will mark how you have your timing set.

With the ignition off, take the distributor cap off,put the van in 4th gear and push forward until the brass bit of the rotor arm lines up with the plug lead for Nr1 cylinder. OK Now disconnect the low tension lead (often green),undo the locking nut (13mm) and lift out the distributor body. I use the locking plate to hold the distributor in a vise. A good blow through with compressed air will do no harm. Under the rotor arm is a felt pad. 2 drops of 3 in 1 oil is good. This is a good time to change points and condenser. Put everything back in place. If there is no real improvement then not much was wrong. Remember, a very small change in the points gap will change your dwell angle.

If you are still not happy, check for air leaks generally on the inlet side of the engine.

If you can find a friendly 'home tune' man or equivalent, then it might be worth getting a diagnostic done, you might be able to improve the fuel economy ( ) enough to cover the tune costs.

Give me details of your ignition system, (as per previous reply), and an idea of your mechanical facilities.

Cordialement,

[sjmtlewy]

Its an electronic ignition - hall sender and all that. Not too bad mechanically, will try most things but dont want to risk breaking anything when its more or less alright

[sarran1955]

Hello,

As the American said ' If it aint broke dont fix it '

Having said that, I had so much difficulty with my Hall sender unit and amp,(frankly I wouldn't really call it electronic ignition ) on my latest 1981 1600 CT engined T25, that I ended up fitting a mechanical T2 camper distributor, and doing away with with those fragile contacts and so on. The only techy bit is to change the vacuum advance diaphragm. Remove the one with 2 pipes off your current distributor,and fit it to a standard beetle/bosch one. You will need a fine pair of circlip pliers. Dismantling is described in Haynes.

I am getting slightly better MPG, but definitely much smoother acceleration, and it is so much easier to set up . It's also very useful when I go into Eastern Europe, (F1 grand prix fan), where I can retune for lower octane petrol. (2nd set of marks on the distributor base).

I have no difference in idle speed or tickover, (which is what the Hall effect was used for in the first place)

Cordialement

[dugwiththevwbug]

have you a 009 dizzy on a 2ltr Aircooled by any chance as 009's are no good for cu engines?

[sjmtlewy]

I dont think my vacuum unit has two connections - just the one on the top.

[dugwiththevwbug]

what engine do you have?

[sarran1955]

Hello!

'I dont think my vacuum unit has two connections - just the one on the top.'

Okay, where does the other end of the flexible go... into the inlet manifold (little brazed pipe) or a plastic spigot on the air cleaner intake.

If its the latter, make sure it's not cracked. If you put a drop of oil round it does your tickover speed increase.

Do you have servo brakes,with a furry vacuum pipe on the left hand inlet manifold (viewed from rear of vehicle) Is it a good tight fit and the hose in good condition

This wont stop you considering a mechanical set up , if anything it's easier.

Cordialement,

[sjmtlewy]

'82 1.9 DG

It has this advance: http://www.brickwerks.co.uk/components/ ... engvac.jpg


It goes into a metal pipe on the back of the carb (side towards the front of van, the righthand of two pipes as you look from the rear)

[sjmtlewy]

And yeah - I've replaced the servo hose from the inlet with a nice new one. The old one was very iffy and had a take-off to a seriously suspicious old after-market cruise control, which I've since ditched.

I'm not really adventurous enough to start playing with replacing things with alternatives. I'm happy just to have the original setup working correctly.

[dugwiththevwbug]

60 mph on a dg is very slow should be able to hit 80mph+ at a push.
when your sucking on the vacumn and the plate is moving are you plugging the end of the vacumn with say your tongue and its still returning? if so probably the rubber diapraghm is perished and you would need to replace with the part in your picture.
If it is holding then that should be fine.and maybe gently lubricate the small felt pad in the centre of the spline once the rotor arm is removed and run a drip down the outside of the spline aswell this should save you dismantling the circlip and vane etc allthough its allways best to remove everything back down to the advance weight pivot and contact. as long as you dont move the body of the dizzy then timing remains the same.
Timing may be out as may many other settings carB etc.

[sarran1955]

I take it you have the original air cleaner, recent filter

Otherwise, relax and enjoy, the French saying is You can never make a race horse from a pack mule

Cordialement