Repairing vacuum advance?

[bran100]

They seem to be pretty pricey, so I'm wondering if I can just clean and repair my current unit. The post doesn't advance with acceleration. I haven't dug any deeper into it than that.

What symptoms does a non functioning advance cause? I'm debugging a mildly rough idle and have tested pretty much every other thing possible. Only other outstanding item is the possibility of valve timing being off, so I'm ordering adjustable cam gears this week.

'82 Fuel injected BTW

[narfire]

Only other outstanding item is the possibility of valve timing being off, so I'm ordering adjustable cam gears this week.

Hmm, want to save some money.... wait and check the valve timing/set up first. The cam wheels have a hole in them and these should line up with either the pointers on the front or a raised rib on the front of the cam towers. This in conjunction with the mark on the crank wheel on the longest point.
If not then the belt should come off and if it has not been changed, now is a good time, and install with everything lined up properly.
I've had the belt one tooth off on one cam wheel and the car ran but not well compared to setting it up properly.(all stock)
In my opinion once it is all lined up get a timing light on #4 and set the timing at idle to 10 Deg btdc....last short pointer. A little white paint on all the marks makes things easier to see with the light.
The adjustable cam wheels are great and make a huge difference in my opinion when you have after market cams and are going to degree the cams to the new cam specs.
I don't know but I suspect the car will run like crap at higher rpms without the vacume advance when it is set at 10 deg at idle. The real car gurus will set us straight on that I hope.
Chris

[BEEK]

if you can set the timing with a timing light where you can set the degree, rev the engine to 4000rpm, set the advance to 32 deg, and wherever it goes back to at idle will be fine, except for emissions purposes, you will need to re adjust the idle, unless compression is high ie high compression pistons, you nay find hard starts or some pinging, you will have to adjust mixture and such. you could find someone who can recurve your distributor. set it for 26-28 deg advance at 3500, and then set timing to about 5 btdc, max advance should be around 32-34 deg with a normal motor. these are from my personal findings

[majicwrench]

Vacuum advance very nice feature. Functioning VA will increase mileage and smooth out idle ( if it works on manifold vacuum) and cruise. Vacuum advance has no effect of full throttle running. I have repaired other (not fiat) units, but really, just buy a new one. Car will be happier.
Adj cam gears are not really going to help an idle issue.
Keith

[rebar1111]

If vacuum diaphragm is faulty, you need to plug the vacuum source to prevent a lean fuel mixture.

[So Cal Mark]

your vacuum advance only operates under high vacuum, light load conditions so it really only affects fuel mileage

[vandor]

> The post doesn't advance with acceleration.

It does not necessary have to. To test vac adv module: pull the vacuum hose off the manifold and suck on it. If you can suck air through it, then it's bad. If it's good you will be able to see the shaft move as you apply suction.

>What symptoms does a non functioning advance cause? I'm debugging a mildly rough idle

The only thing you would notice is 1-3 mpg poorer fuel economy. It does not affect idle because the port that gives vacuum to the advance unit is close by the throttle plate at idle. So it only gets vacuum once the throttle is opened. You should see it move if you open the throttle a bit. However you open the throttle suddenly and a lot, then there will be little vacuum and the vac advance may not move. As Mark said, it only operates under high vacuum conditions (steady throttle driving) and off idle.