Ok, so I was reading the article Camaro69 posted.
http://www.hotrodders.com/forum/dist...1-a-59033.html

And it got me wondering how I am supposed to use a vacuum advance. I have a very large cam in my c10.
A Voodoo 60103. AFR Heads, Victor Jr intake, ect, ect.

I set total timing to 37 Degrees.

I have the vacuum advance plugged off.
To get the truck to idle at 800 rpms in gear, with 5 lb of vacuum pressure the high idle is about 1400 rpm.

If I plug in the vacuum advance the high idle runs up to 2500 rpms. That is way to high. So high that I tried driving it and dropped the tranny. The truck is currently sitting waiting on a new 700r4.

I don't know anyone with that large of a cam running a vacuum advance. So what is everyones thoughts?

 

Did you try adjusting the high idle setting to bring it down to a decent speed?

 

How did you go about setting total timing to 37? What is your base timing set at? Based on your description, I presume you connected the vac advance to manifold vacuum? What type of vac advance can does your distributor have? Most stock cans need at least 15" of vacuum to operate, so you must have a non-stock one for 5" to move it?

 

How can you adjust high idle and low idle separately on a Holley?

The 5 lb is at low idle, about 850 rpms, it has 15 lb at high idle. about 1400 rpms, unless vacuum hooked up then it runs up to 2400 rpms.

The vacuum is hooked up to the correct port on the carburetor. It is labeled vacuum advanced from Holley.

I set the total timing by revving the car up intill the timming stop climing, I then set my timing light to 37 degrees and then set the distributor to 0. I have a very nice timing light. Base timing is about 12 degrees.

My distributor is a billet HEI I got from the local speed shop. Don't remember the brand but it should be close to stock.

 

You should be hooked to the port that's on the metering block. There's another on the base plate for vacuum advance, but it's full manifold vacuum, not metered vacuum. You can see mine connected to the front carb in this picture:

 

Dude, it is hooked up correctly. Really, I read the manual. The port on the metering block is labeled Vacuum Advanced in the manual.

I can find you five other cars that belong to fellow racers that all have the same problem. It is a very, very common issue with large cams.

All of the guys I race with just plug off the vacuum advance.

 

No it isn't. Go back and read that article again...everything, concentrating on the parts about why the distributor wants to be hooked up to full manifold vacuum, not ported like you have it.

 

So Are you saying you want me to hook it up to the pvc port?
That is a new one.

1971BB427 why does Camaro 69 think we have the vacuum advanced hooked up wrong?
Same place it is hooked up on my Camaro, only it has a lot smaller cam.

What good would that do? I already have to much timing. Getting the vacuum advance to add timing will only make it worse.

I need the vacuum advance to stop adding in timing at idle. I don't want the truck idling at 2400 rpms. Adding more vacuum is only going to increase the timing. The truck runs fine at 1400 rpms with about 12 degrees advance. Why do I want it to idle at 24 - 30 degrees advance.

isnt it? Am I missing something here?

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg.

I dont have low vacuum at idle. I have 5 hg at low idle, but in park i have 15 hg, which is opening the advance and adding in additional timing, which is then increasing my idle even more. Adding more vacuum will only make it worse. I need less vacuum at high idle or more vacuum at low idle.

 

By what you just asked, I can tell you didn't read the whole article, or didn't get it. You can't hook up to manifold vacuum using the vac can you currently have, that's described in part 2. The can needs to be rated at 2" below your vacuum at idle. And since you're coming off idle while in gear (driving), I would focus less on your free-idle vacuum reading. Things aren't working right for you the way it's hooked up now, so you need to fiddle with it. And of course the manufacturers show hooking advance to ported vacuum, parts they sell have to conform to emissions. The distributor didn't used to be hooked up that way until emissions regulations required the engines to run on ported vacuum so they would conform. Again, that's all described in the article too.

 

Ok, so start over. I am apparently missing something in that article.

So, that port on the carburetor is refereed to as ported vacuum?
Then, manifold vacuum refers to the lower port on some older Holley's or making a hole in the manifold, or using an adapter plate with a vacuum port?

Where do you want me to start checking vacuum levels?
Im guessing I need to make some sort of adapter to try testing the pvc port?

That carb is clearly not emissions legal and was not designed to conform to emissions. Therefore, I didn't feel they would porly design a racing carb. It say all over it not for street use, not street legal, racing applications only.

There are not any holes or places for a vacuum line on a victor jr intake. Again it is only for racing applications. I do not want to drill a hole in it, just to test a theory.

"vac can", what? I don't have a vacuum can. There isn't a single stock piece on this truck. I removed tune port fuel injection. Just for info I had the same idle problem with tune port injection, due to the size of the cam. Idle isn't even controlled by vacuum and I had issues with it idling to high.

So, im lost. I have read that article 15 times. I am clearly not understanding something. I am not trying to argue. I really do respect your input. But please start from the beginning.

I just tested the ports on the camaro. Upper port that Holly says to use has 12 lb of vacuum at High Idle while the lower port has 10lb of vacuum.