help me understand my vaccum advance

[datfreak]

Hi all-

I just did the e80-early 80's skyline electronic dizzy conversion on my '71 240z- and I'm amazed at the difference-ie easy to start(dont need hardly any choke now) and seems revver.

The vaccum advance units is stuffed in the electric dizzy but I've ordered a new one and will have it this week.

Now my question.

The vaccum hose off my carbie(std 240z carb- takeoff on left one) has no vaccum at idle but has lots of vaccum on open throttle.

So.. the dizzy will advance at open throttle but not at idle.

Shouldnt it be the other way around???with lots of vaccum advance at idle,then retard to normal at throttle to prevent pinging?

If im right, shouldnt i take vaccum from the balance tube instead of the carbie, so there is advance at idle?

Anyone like to share some ideas?

[sideshowbob]

Nononono. The vac advance helps improve your idle gas consumption. Your car runs with less gas and therefore needs retarded timming at idle, otherwise detonation can occur. On acceleration, more fuel is dumped in and the advance can be increased for more power.

Where did you find a new vac module? I need one!

The vacuum off the carb is called 'ported vacuum' and is usually the opposite of your regular manifold vacuum. More throttle=move butterfly opening=more vacuum. Hooking up the advance to the manifold vac is a BAD idea.

[jmortensen]

Huh??? Bob, that don't make no sense.

Datfreak, you've got it right, there should be more vacuum when the plates are closed, because the air can't get in to fill the cylinders. When you open the throttle plates, the restriction to the incoming air is lessened and you get less vacuum.

You will get vacuum at part throttle, really the only time you have almost no vacuum is at WOT.

Not sure how you're measuring or why you aren't showing vacuum at idle though. Maybe a vacuum leak, like at the bushings on the throttle plate perhaps.

[datfreak]

I always thought that the more load a motor has the more chance of pinging-

so a motor needs to be less advanced(at the same rpm) under throttle vs a motor with no/little throttle.

But i may be wrong(it happens alot)

Im getting my vac unit from a place called dizzy world in Australia.. at $80au (?$50us?)

[sideshowbob]

Jmortensen - Ported vacuum, PORTED VACUUM is higher when the throttle plate opens. It it the opposite of MANIFOLD VACUUM.

[sideshowbob]

Let me reiterate: THE VACUUM ADVANCE PLUG IN TO PORTED VACUUM WHICH IS SUPPOSED TO BEHAVE THE WAY YOU DESCRIBED IT. LEAVE IT THERE.

Ok, that is all. Thank you.

[sideshowbob]

http://autorepair.about.com/library/glossary/bldef-626.htm

[=Enigma=]

Hey Tony, I believe you can get a vacuum unit for the 280ZX dizzy at VB.

[jmortensen]

You're right. Sorry.

[datfreak]

thanks bob for getting me on the right track..

I nearly changed stuff for nothing.

[sideshowbob]

It's ok, I just don't want him wrecking a perfectly good motor (had I been a bit more careful with the flooding, mine might still be salveagable. Still not entirely sure if it was the injectors leaking down or the AFM or what, really).

Err, how did you know my name?

[sideshowbob]

PS: What's VB? EDIT: Victoria British, oops and I have their catalog here somewhere too!

Edit#2: 60$ for that little peiec of crap?!?!?! This is highway rubbery. I'll get back to you when I've come up with a method to repair my old one with liquid electical tape or bubble gum.