thevetterisbetter

Anyone know of someone who has this item in stock? Don't want to go to Dr. Rebuild or Corvette Central.

Stewart's74

NAPA.

Cali,68,L-79

Napa. Determine what amount of advance you need from timing with VA disconnected to get 36 degrees at 2500RPM. Optimal is no greater than 54 degrees by 4000 RPM w/ VA and the VA listing are on LARS website or IM him for stock #'s. I got mine from NAPA, $12, and it works flawlessly.

:cheers:

thevetterisbetter

I just need one that works! The vacuum advance doesn't start moving until 8 in of Hg are applied. According to my service manual, it should be all in at 10-12. I don't understand what would cause a vacuum advance to need more vacuum to move it as opposed to needing less vacuum. I assume the spring would wear out and loose tension, not gain it.

redvetracr

Autozone..about $6.00

SpyderD

Seems that is typical with a stock unit to start moving at 8 Hg. Nothing abnormal to that. They are usually all in by 12-14 Hg.

If you don't have emmission testing I would very quickly rip out and throw out that page in the service manual about timing and advance away and curve for perfomance anyways. That would mean tuning the vacuum advance with a quicker timing curve. The result is better performace and better fuel economy.

thevetterisbetter

When I disconnect the vacuum advance to the carb, there is no difference at idle. I checked the amount of vacuum that I have the VA hose hooked up to on the carb and it is pulling out about 10-12 in. of Hg.
Also, the engine is no longer stock, the stock VA is a B1, the engine is now a 388 stroker.



[Modified by thevetterisbetter, 5:11 PM 5/17/2004]

thevetterisbetter

Cali
What made you go with the VC 1810? Is it a more performance based VA?

SpyderD

Hmmmm, no difference at idle - I would say you have your VA connected to the "ported" source which would be close to zero vacuum at idle (vacuum starts when you open the throttle) EXCEPT that you say you read 15 HG from the same source. I thought you said the VA was moving at 8 Hg? Are you sure you are taking the vacuum reading from the same source - ported source vacuum - above the throttle plates, has almost no vacuum at idle; manifold source vacuum - below the throttle plates, has vacuum at idle.
If so then indeed you have a defective VA, pick one up at NAPA, Autozone, etc. for $10 or so.

If you get a new VA get one of those crane adjustable VA's.



[Modified by SpyderD, 6:25 PM 5/17/2004]

Cali,68,L-79

Becuase I was getting 36 degrees@2500 and this one would not allow the total timing to go above 54 degrees even at or up to redline. LARS picked it for me.

thevetterisbetter

Spyder
I took the top of my distributor off and hooked up a vacuum pump with a gauge on it and checked the gauge when the distributor actually started to move. This was at 8 inches of Hg. It was all in (the distributor stopped moving) at about 16 inches of Hg. Now, in a separate test, I hooked up a vacuum gauge to the port of which I have the VA hose from the distributor normally hooked up to. This showed a reading of about 10-12 inches of Hg.

thevetterisbetter

So Cali, at what vacuum does your VA start work then?

SpyderD

I'm really stumped, you know your VA works because you hooked up a guage directly to it, you know you are getting vacuum from the port...could it be something as simple as the rubber line between the VA and carb port plugged with crud? A hole in the rubber line?
I do know one potential problem you could be facing - you are indeed correct you need a VA that brings it all in before your idle manifold vacuum if you use that source. I would think right now your idle speed is dancing all over the place (up and down in RPM) since timing is increasing searching for the right point. If that is the case a simple fix would be to hook it up to a ported vacuum source. This SHOULD be your problem, but then again you are just saying the vacuum is not getting to the VA at all....

Cali,68,L-79

12HG.

thevetterisbetter

Spyder
I'm not sure what carb you are using in your explanation. I have a Q-Jet for a 74 four speed. There is the side port (near the choke), that draws very little vacuum. There are the ports for the PCV system and vacuum system for the lights on the left front side (viewing it from the drivers side, on the engine). Then on the right side, there is an upper port and a lower port in the airhorn. I have the VA hose plugged into the upper port and the lower port in the airhorn plugged off. The reason I used the upper port is because it seems to draw the most vacuum than the other two plugged off ports.

Stewart's74

My set up was also recommended by Lars. He had me hook up the vac advance on the front of the driver side of the carb.

SpyderD

I am familiar with Holleys but every carb should have a ported (above the throttle) and manifold vacuum source. Which one to use is a matter of personal preference and based on weather you need that vacuum timing advance at idle or not, otherwise after idle there is absolutely no difference.

BUT - if hooked up to the manifold vacuum source at idle and you don't have enough vacuum to pull in that full VA you will never be able to tune it right at idle.

thevetterisbetter

Stewart
At what port? My Qjet doesn't have a port available on the drivers side. The passenger side there are two, as I stated before. The one up high and the other lower at the airhorn.

thevetterisbetter

Cali
You mean it's all in at 12Hg?
Lars recommended that VA for myself as well.

Stewart's74

My bad....The port is on the front of the carb towards the drivers side.