Club 80-90 Forums

Hi need 2 questions answering if you could please.

1st, What is a Vacuum advance unit do?

2nd, How do i test this is working ok? (as when i remove the pipe to it the idle returns to normal from fast idle)

Thank you

it advances the timing according to vacuum pressure due to inlet manifold pressure, ie fater the revs, higher the vacuum, mor advance.
Vac unit must be disconnected and the pipes blocked to the inlet (or carb depending on which engine) when doing the timing and the timing and idle set up according to the engine spec, at idle there is virtually zero manifold vacuum at the throttle body on a DJ, but at the carb on a DG I think there is some, hence a slight rise in revs when you connect it
the distributor also has a mechanical advance so faster it spins the more advance there is, often the mechanical advance fails and you get an erratic idle that is noticeable on the timing gun

simple test is remove disi cap and rotor and plastic cover so you can see the internals and then apply vacuum by mouth to the vac advance unit and you should see the arm pull the internals in an anticlockwise direction

simple test is remove disi cap and rotor and plastic cover so you can see the internals and then apply vacuum by mouth to the vac advance unit and you should see the arm pull the internals in an anticlockwise direction[/quote]

Did what you said and nothing happened except i could hear a diaphram move??? Does this mean it needs replacing? thanks for your help

yes you should see stuff move inside the dizi with cap off when you suck. Replacement diaphragm unit

DG ENGINE 1.9
http://www.brickwerks.co.uk/shop?page=s ... ory_id=122" onclick="window.open(this.href);return false;

DJ ENGINE 2.1
http://www.brickwerks.co.uk/shop?page=s ... ory_id=122" onclick="window.open(this.href);return false;

Aidan wrote:it advances the timing according to vacuum pressure due to inlet manifold pressure, ie fater the revs, higher the vacuum, mor advance.

often misunderstood....please read the link.

It advances the timing according to the amount of vacuum in the inlet manifold...Maximum vacuum happens at relatively small throttle settings at speed ie: cruising on a fast road at 55mph ie: slight throttle but highish continuos speed creates a weak mixture, this needs extra ignition advance (provided by the higher vacuum pull on the distributor base plate) to burn properly.
So it is at idle or cruising speeds with little or no throttle where vacuum is produced, wack your foot down on the accelerator and the vacuum disapears. This is because the butterfly has been opened allowing normal atmospheric air pressure to enter the manifold.

SEE:
http://en.wikipedia.org/wiki/Manifold_vacuum" onclick="window.open(this.href);return false;

Martin

thanks for the correction Martin

Thanks for all your help will get a replacement ordered tomorrow and will update on the progress. Talking of progress its amazing how much more power i've managed to get from an old engine just from changing the plugs, leads, air filter and cleaning the carburettor out with a tooth brush and replacing all the servicable parts!

Oh just one more question if i could be cheeky (i have so many but trying to space them out lol) is there anyway of replacing the studs that the air ducting bolt onto the carburettor? as the thread has been stripped from age.

Thanks

use a stud extractor?

get the parts first before you remove them

kevtherev wrote:use a stud extractor?

get the parts first before you remove them

do you know which studs i mean? It's the 3 on top....



Thanks

Hi,

I have some 2nd hand studs (removed when fitting lpg mixers as they need longer studs). PM me if interested.
If you want new ones try here http://www.gowerlee.dircon.co.uk/2E3type.html or maybe gsf.

Vac advance - when you suck on pipe does it pass air (ie is the diaphragm leaking)? If so, vac unit is fubarred and needs replacing (can just replace vac unit, instead of whole dizzy). If not passing air the mechanism is stuck and could be freed off (try "helping" the vac by pushing the pull rod in the dizzy whilst sucking). If diaphragm housing has taken a bashing, could be bent which will cause this. Have straightened them successfully, but can't guarantee advance curve will be exactly right (but it's better than none!).

Cheers

Andrew

Yes those studs pictured
they are not very tight.

kevtherev wrote:Yes those studs pictured
they are not very tight.

Is it just screwed into the Carb??

So retested the sucking on the vac pipe again but this time harder and it does move things in the distributor!! So back to square one with the high revs seems to be getting worse too!!

Think the penny has dropped what is happening here. The idle is ok when the choke is on but as the choke is coming off the idle increases! So does this mean its a simple mixture issue? (simple used losely!)