Vacuum advance test

[TheLowRanger]

I have been wondering whether my vacuum advance is working properly as my fuel economy (if I can use those words when describing a V8) is more than what I think it should be. I did a search through old threads and found one that said if I suck through the vacuum hose that it should hold pressure if it's working properly. When I suck, I just continually suck air (even though it's hard work cos the hose is so small) it doesn't seem to be holding any pressure. Does this mean that my vacuum advance is stuffed? Any help would be appreciated, thanks.

[Tank]

Suck the end of the hose and put the tip of your tounge over the end of the pipe to seal it, your tounge should stick to the pipe (vacuum) when you open your mouth. Alternatively, remove the Dissy cap and suck (very hard) on the pipe (hose) and watch the dissy guts to see if it rotates a small amount, if you can get hold of a vacuum pump to test with, it will save you having a puckered up look for a week or two, Regards Frank.

[TheLowRanger]

Thanks Frank, looks like it's not holding vacuum. Anyone got any advice on where I can get a new one for a good price? Doesn't really matter where as I will have to get it sent to me. Funny thing that, but there doesn't seem to be any Land Rover parts/service gurus up here in the Kimberley's.

[Bulldog]

Ok guys, lets go thru this again for the slower ones ;)

After reading the first 2 posts, i went out to Bulldog and sucked on the hose. Nothing :o.

So let me just check that this is the hose that goes from the dizzy to the manifold between the carbies (suck on the manifold end), right? I am getting nothing at all (no movement in the dizzy and no suction at all. I can't even manually turn the inside of the dizzy...

Mine has an electronic ignition conversion (opto wheel in the dizzy, no points). The advance is still meant to operate isn't it?

Could this explain some of my overheating problems? :(

$176 for a new replacement :eek: Does anyone know of a better price than that?

[Lucus]

Thanks Frank, looks like it's not holding vacuum. Anyone got any advice on where I can get a new one for a good price? Doesn't really matter where as I will have to get it sent to me. Funny thing that, but there doesn't seem to be any Land Rover parts/service gurus up here in the Kimberley's.

Hi mate, I got one from rovacraft for $80, Might pay to give Discovery Autos in wanagara a ring too as they are very competitive with there pricing. Takes about 10mins to change but the unit is held in with torx bits if i recall correctly. I "think" they may be slotted so you can use a small flat blade screw driver. A small allen key also works. I would recommend a small drop of loctite medium strenght on the screws to stop them working out.

cheers
Luke

[cockie55]

try this thread

http://www.aulro.com/afvb/technical-chatter/31334-vacuum-advance.html

[PLR]

Ok guys, lets go thru this again for the slower ones ;)

After reading the first 2 posts, i went out to Bulldog and sucked on the hose. Nothing :o.

So let me just check that this is the hose that goes from the dizzy to the manifold between the carbies (suck on the manifold end), right? I am getting nothing at all (no movement in the dizzy and no suction at all. I can't even manually turn the inside of the dizzy...

Mine has an electronic ignition conversion (opto wheel in the dizzy, no points). The advance is still meant to operate isn't it?

Could this explain some of my overheating problems? :(

$176 for a new replacement :eek: Does anyone know of a better price than that?

G`day , Pete

Yep that`s the right pipe .

Pull the cap off and turn/swist the rotor this movement is the mechanical advance , the plate movement is the vacuum advance .

Don`t know your specific ignition being aftermarket , does the amplifier/CDI ? box have a name on it ?
It could be that your type has an electronic advance and so doesn`t use the mech or vac .

Performance ignitions in Nunawadding i think they are called do a change over vacuum unit for around $60 +- and being not too far from you if you drove it in they could advise you about which advances it should use .

Cheers

[Bulldog]

Pull the cap off and turn/swist the rotor this movement is the mechanical advance , the plate movement is the vacuum advance .

Don`t know your specific ignition being aftermarket , does the amplifier/CDI ? box have a name on it ?
It could be that your type has an electronic advance and so doesn`t use the mech or vac .



Thanks PLR,

Whats the mechanical advance? I was under the impression that the advance is set with a timing light and then the vacuum adv adjusts it for RPM differences... Is it a system of weights etc?

The elec ignition box is fairly simple and only connects to the dizzy. It is called "Optospark". However if it was clever, it could get the RPMs from the opto wheel in the dizzy and do the advance that way.

Any ideas? Thanks again and apologies for the thread hijack ;)

[cockie55]

Bulldog you say "Whats the mechanical advance?"

If not electronic advance as all but more recent LR's there is actually 3 X types of advance settings and parameters...initial, mechanical and vacuum that generate the total timing at any one time.

Here is good explanation:

Ignition Timing (http://www.centuryperformance.com/timing.asp)

[PhilipA]

You check the mechanical advance by turning the rotor slightly clockwise . It should move say 2-3mm
When let go it should spring back to its original position.

If it does not do either of these things, take off the rotor carefully and drop some oil down the centre. It may help to undo the small screw inside.
Wait for several hours then gently try again.And so on.

As explained the centrifugal advance compensates for the different advance of the spark timing as revs rise.

The Vacuum advance is an additionbal amount of advance that is only active under light load, when the engine can take much more advance without pinging. Its ther efor maximum economy while cruising.

Both will affect economy, but no centrifugal advance may cause the engine to run hotter under load as the engine is retarded.

It needs quite a suck on the vacuum diaphragm, and the test is to suck hard and stick the end of the tube onto your tongue. it should stay there indefinitely,but you may talk funny.
Regards Philip A

[PLR]

Thanks PLR,

Whats the mechanical advance? I was under the impression that the advance is set with a timing light and then the vacuum adv adjusts it for RPM differences... Is it a system of weights etc?

The elec ignition box is fairly simple and only connects to the dizzy. It is called "Optospark". However if it was clever, it could get the RPMs from the opto wheel in the dizzy and do the advance that way.

Any ideas? Thanks again and apologies for the thread hijack ;)

G`day Pete ,

yep weights , sort of like making a fist and then extending your pointer , that`s sort of how the weights work , 2 of weights 2 of springs . Weights are a sort of half moon shape and pinned at one end they are held closed by springs and as the revs increase the weight spin and open , like your pointer . These control the mechanicl or centrifugal advance .

This is the movement of the rotor that should be there with the cap off .

If your Optospark is a 400 or 500 i`m pretty sure they still require the use of the mech and vac advances . Probably got USA and made under lic in AUS ?

I have a similar Pommy made 1 and it requires both advances it`s made by Newtronics but Piranha here .

If you`ve ever had trouble getting the rotor arm off , it`s common to dislodge the mech adv if too much upward force , which dislodges the weights and springs , the only way to get them back is to dismantle the other thing they do is seize up , either from a build up of crud and rust type stuff or the pins wear/springs etc wear .

Follow your manual if you intend to dimantle the dissy and mark anything to do with the Optospark and be very careful with the opto wheel they can be very fragile , the pommy made one is actually more robust than the Yank one .

Cheers

[LoveMyV8County]

If you've had a point dizzy converted to breakerless ignition you may want to check that the arm that does the vacuum advance is connected to the base plate.

If I recall correctly, on my County there was a locating pin on the points that also made the connection between the base plate and the vacuum advance diaphragm.

A simple test to see whether it's operating is to connect up your timing light and as you rev the engine the timing mark on the pulley should move steadily away from the pointer.

Chris