How much vacuum should I get from the port that goes to the vacuum advance when the car is idling at 850rpm.

My carb is getting about 15 inches and it is pulling a lot of vacuum advance into the timing equation. is this normal.

1983 camaro LG4 with quadrajet. No electronic controls except choke.

When setting the timing at idle around 700 rpm with the vacuum line to the distributor plugged car idles ok then I plug in the vacuum line the car acelerates to around 1200 rpm and the timing goes up about 14 degrees what gives. is this normal also????

 

Sounds to me as if you have the vacuum advance plugged in to manifold vacuum rather than ported vacuum. You should not have any vacuum advance at idle.

 

Thanks for the reply.
That's what I thought but I checked and I have the vacuum line plugged into the correct port. It is plugged into the front driverside port on the Qjet.

At what Rpm should there be no vacuum?
What would cause it to have vacuum at idle?

 

Two things can cause a vacuum. The first would be being plugged into the wrong port. The second would be that you are idling to fast and you have the transfer slots exposed in the carb but at 850 rpm I think this is unlikely..

Put your finger over some of the ports on the carb you will feel the vacuum on them if there is any. Usually a ported vacuum nipple is higher up on the carb.

 

I have plugged my vacuum gauge into all of the ports to see if there was some other place I could get vacuum from that was low at idle. NO deal.

The idea of having the transfer slot exposed due to too high of an idle seems to make sense and when i turned the idle down to about 600 rpm it did decrease a little. There is a round air restrictor thingy in the line that goes to the distributor vacuum advance it has two vacuum lines that come out of the side of it and go into what looks like it is probably a temperature activated switch that is screwed into the top of the thermostat housing. Is this thing supposed to reduce the vacuum pressure?

 

It's just a matter of preferrence with regards to manifold or timed vacuum advance.

:hail:IROC-Z

 

I've always prefered for street cars to run the vacuum advance on manifold vacuum.

They tend to idle smoother, get better fuel economy, and seem to have a bit snappier throttle responce in the midrange. When you stand into it, it just uses the mechanical curve, which i set for WOT power.