HEI Vacuum Advance question.

[airman]

When I set the timing to 12* btdc (vac advance line off and plugged at 800 rpm) it idles very nice. Lock down the dizzy and attach the vac advance line and I go from 12*btdc to 38*btdc and increase 300 rpm.

What am I doing wrong here? I cant find an adjustment on this proform dizzy to change the advance. Any comments would be welcomed.

TIA, Jeff

 

[NYLES]

Id say either on wrong vacum port or need to ajust diafram its inside the spout where vacum line connects all the way in is locked out and If I remember one turn counterclockwise equals 2 degrees of timing. Adjust with a allen wrench. Also could need different springs.

Its been awhile but thats what I remember...

Also idle carb back down to 750-800 with vac connected you cant adjust only oneat a time, best is to hook up vacum gauge and get the carb and timing in sink, showing most vacum.

 

[NYLES]

And you want it to be at full advance at about 3000 rpm, I aint real fresh on this cuz fact is I aint touched a carb or a dizzy in about 6 months...my warm 302 idles with 16 degrees advance at 650 rpm but it aint stock...if your in a ford tuning book with a aftermarket cam....aint goona work..comp cam says run mine with 22-36 degrees total timing

best bet get a vacum gauge

 

[airman]

I have a gauge. I read around 19" before it sounds funny. I'm looking for the greatest vacuum where it still sounds good right? Vac line is to the manifold port on the Holley carb.

I tried the allen wrench but didn't find one that fit. Is it a really tiny allen?

Thanks again.

 

[ransil]

I have a gauge. I read around 19" before it sounds funny. I'm looking for the greatest vacuum where it still sounds good right? Vac line is to the manifold port on the Holley carb.

I tried the allen wrench but didn't find one that fit. Is it a really tiny allen?

Thanks again.

You want ported vacuum, no vacuum at idle.

 

[airman]

I may be wrong with this, but I think of the 3 ports on my Holley TA the only one that has zero vacuum at idle is the one to my PCV. The one that has been connected to my vac advance is below the plate and has manifold vacuum. Its where the manual says to put it.

That would only make sense if the vac advance only advances timing with less vacuum because the tightest manifold vacuum would be at idle. I'm trying to get this but I still don't.

I do think I figured out my first issue though. The distributor has a mechanical AND a vacuum advance. The mech advance engages after 800 rpm which sort of explains the increase in rpm and advance. I have also found out that the vacuum can is not adjustable so I will be off to find a new can today that is.

With all of that I think I was using at least a little of the primary circuit to idle and that explains alot to me about failing emissions last year and my high vacuum. I think I had to retard it so much to run at highway speed without pinging that I had to adjust the idle screw into the primary. I may really gain some power if I can reduce the total advance.

What rpm do you guys with auto trans idle at in D?

 

[DirtDonk]

You're on the right track airman, but definitely have something amiss.
The PCV is always to full manifold vacuum and should be a large 3/8" diameter port. So that can't be the one for the vacuum advance since it's just a small (1/8"?) type.
Some cars did use full manifold vacuum to the distributor, but most don't. The Broncos run best with timed/ported vacuum as was mentioned. So find the small port above the plates and see if it has vacuum at idle. That one should have none, or at the most a very minimal amount of vacuum at idle.
If it has full vacuum then your throttle blades are not being allowed to close down far enough and are exposing the port to full vacuum.

Got any pics of the layout we can look at?

Paul

 

[Broncobowsher]

You're on the right track airman, but definitely have something amiss.
The PCV is always to full manifold vacuum and should be a large 3/8" diameter port. So that can't be the one for the vacuum advance since it's just a small (1/8"?) type.
Some cars did use full manifold vacuum to the distributor, but most don't. The Broncos run best with timed/ported vacuum as was mentioned. So find the small port above the plates and see if it has vacuum at idle. That one should have none, or at the most a very minimal amount of vacuum at idle.
If it has full vacuum then your throttle blades are not being allowed to close down far enough and are exposing the port to full vacuum.

Got any pics of the layout we can look at?

Paul

What he said

Big 3/8" port is PCV
2 little 1/8" ports. 1 is full time vacuum. 1 has little to no vacuum at idle. The no vacuum at idle is the one for vacuum advance. There is vacuum there at cruising speed (vacuum at part throttle).
Impossible to get a good vacuum signal there under load (no spark advance under load)
Good vacuum there under part throttle cruise (low load, advance spark for better performance and economy)
Mechanical advance is there becasue it takes a fixed time for fuel to burn after getting the spark. That time remains constant but at faster engine speeds you need to throw the spark sooner so the big fireball actually happens at the right position of the crankshaft.

It's all a balancing act. Throw the spark sooner at faster engine speeds so the peak cylinder pressure happens at the right time with the delayed burning gasoline. Then add additional vacuum at cruising speeds due to the reduced cylinder pressure of an engine pulling vacuum at cruise. Too much here, not enough there, comes on too fast or too slow...

 

[airman]

I feel so stupid. I should have never put that keg fridge in the garage.

Wrong port. Its amazing how many guys it takes to tell me the same thing before I get it.

Thanks. Jeff

 

[needabronco]

Don't feel bad, I've done the same thing:-X

 

[Broncobowsher]

I feel so stupid. I should have never put that keg fridge in the garage.

Wrong port. Its amazing how many guys it takes to tell me the same thing before I get it.

Thanks. Jeff

I could come over and help you empty it. I wouldn't even charge that much for helping either

 

[NYLES]

Airman, that keg comment reminds me of what I had been doing about half the day before I gave you the first responce! Mines just a little fridge but sometime during the day somebody left a 12 pack in it! So I wasnt real clear on it all! Sounds like you got it though!

And I did play with my running chasis sat...runs 17hg at 22 degrees timing and sounds great....I do have one disadvantge right now as I cant put it in gear!(still a running chasis)(wife says sometime I look like that commercial with the guy in his stang revin it up in the garage) I also fixed a flooding front bowl...I run a 575 speed demon vac sec, and a comp cam 262 extreme energy....I do not however have to pass a smog check.

Yall wish me luck glass body soon to be enroute! Hope to have driveable by my Bday in July!

 

[airman]

I could come over and help you empty it. I wouldn't even charge that much for helping either

Oh, You're good, but nobody is that good! Well maybe Bob McKenzie. We had a small superbowl party yesturday and I had a 1/2 barrel, a 1/4 barrel and a 1/6 barrel in the fridge. I needed to hold the door closed with a rope until we draind the 1/6 barrel.

You should come over and give it try though. Let me know when you're near Greenfield and Queen Creek. I am getting my new Tuff Shed this weekend so pretty soon my garage and work bench will be presentable.

Thanks guys
Jeff