vacuum advance - how much movement to expect?

[8ball]

Hello again,

Following on from my last thread about Pierburg 2e3 problems, I received my carb back from Bromyard in brilliant nick and reinstalled. Initial results were promising, after setting the choke with a press/release of the accelerator, started first turn of the key, at a high idle, then revs dropped with a blip of the pedal, as should happen. After some tinkering, hot idle was achieved, and the van is now idling at cold, and hot, and the issue with stalling at junctions seems to have gone. It's still not right though, the easy start on first installation has disappeared, and the pedal needs to be depressed and held in order to start. The idle is still somewhat erratic, and the van feels really gutless in 4th and 5th, struggling to make 60 on the flat and having to drop to 4th on mild inclines. I've checked through past threads, and there are a few mentioning problems with the vacuum advance unit. Earlier today I removed the distributor cap, disconnected the vacuum pipe from the carb to the distributor and sucked as hard as I could, but couldn't see any movement of the connecting arm from the vac advance unit, so I removed it and a freed it up a little. Sucking directly on the nozzle on the unit produces inward movement of only a few mm. When I put it back onto the distributor and sucked again, this translated into movement of maybe only 2-3º, does that sound right? How much advance should be provided by the centrifugal action and how much from the vacuum unit? When I put the distributor back in and took the van for a spin, it seemed to have a little more guts, or maybe that was just wishful thinking?

[ghost123uk]

Is this any help

Max Vacuum advance is quoted as 12~16 degrees for both DG and DJ

As for the centrifugal advance, there is a graph in the link below and it looks like 30 @ 4,000 rpm
I didn't realise it was that much Esp when you add 16 for the vac = 46 degrees btdc

From our wiki on the subject and there is lots more in the article HERE.

Vac units available from Brickwerks but a bit pricey

[jamesandtheopenroad]

I have exactly the same symptoms on a Solex carb. Its been cleaned, reset, all gaskets changed, ignition parts changed etc etc.

Have ordered a new vac advance so will take the dizzy out, clean that up, make sure the cent advance is free and see how we go. Will let you know.

[HarryMann]

Has it got both vac adv and retard? Not sure if the DGs had that. The late aircooleds did
NB. Do not swing the dizzy if you haven't scribed a good clear mark between the two faces.

[8ball]

Has it got both vac adv and retard? Not sure if the DGs had that. The late aircooleds did
NB. Do not swing the dizzy if you haven't scribed a good clear mark between the two faces.

Just the one inlet, so presume that's vacuum advance only?

e exactly the same symptoms on a Solex carb. Its been cleaned, reset, all gaskets changed, ignition parts changed etc etc.

Have ordered a new vac advance so will take the dizzy out, clean that up, make sure the cent advance is free and see how we go. Will let you know.

Thanks James, how will you go about checking the centrifugal advance?

Cheers

Chris

[kevtherev]

The mechanism is driven by weights
Ensure thes are free to move and they operate the advance by moving them

[jamesandtheopenroad]

NB. Do not swing the dizzy if you haven't scribed a good clear mark between the two faces.

Sorry, not sure what you mean by "swing". Literally swing? If so, what does that do?

[ghost123uk]

Rotating it axially, like you do to adjust the timing

[jamesandtheopenroad]

Right.

So a mark on the body of the dizzy and a mark on the engine before removing so I know where to put it back?

[ghost123uk]

Right.

So a mark on the body of the dizzy and a mark on the engine before removing so I know where to put it back?

[HarryMann]

...and make sure they are accurate, and push it right down when it goes back in

[HarryMann]

Don't forget that 1 degree at the dizzy is 2 at the flywheel
So 20 degrees advance is only a movement of 10 deg at the dizz

[8ball]

Thanks for all the replies and advice so far. With all my waffle in the OP, I think my original question got a little bit lost. namely, how much movement of the control arm should you expect to see when sucking really hard on the inlet on a fully working vac advance unit? With mine the movement is probably no more than 3 or 4mm. Does this sound right or should there be more? I'm sure my my attempts at sucking are nowhere near as powerful as the vacuum achieved from the manifold, but it did seem to be quite an effort to get the control arm to move. I'll happily buy a replacement from Brickwerks if I can determine that it's at fault, but I don't want to go spending £40 unnecessarily.

[HarryMann]

Of course you don't, money's hard enough to earn!

When your foot is hard down, the vac isn't doing anything, so if the prob manifests under those conditions, then it's unlikely to be that.
It is basically an economiser, that advances as the load comes off the engine for cruise and light load, and as the mixture weakens down.

Has there been any popping or backfiring on light load ot overrun?

[8ball]

So when your foot is hard down is the dizzy just relying on the centrifugal force? I'm a bit confused! No popping or backfiring or overrun.

Don't forget that 1 degree at the dizzy is 2 at the flywheel
So 20 degrees advance is only a movement of 10 deg at the dizz

Okay, well to my mind that seems to lessen the likelihood that it's the vac advance that's necessarily at fault as there is definite movement. I'm going to buy a timing light to check everything's as it should be - this should also give me confirmation one way or the other that the vac/centrifugal advance is working, no?

SO... if it turns out not to be the vac advance, what could the culprit be? Coil? It looks like it's very much the original unit, do they degrade much with time? Bearing in mind this is a 30 year old engine but with only 25k miles (although has been stood resting for a number of years). What would be the best procedure for checking its integrity? I've can borrow a multimeter but I'm not exactly sure where to go from there, so if someone could explain I would be mega grateful!

Cheers

Chris