Brought to you in part by:
CarParts.com!

*Photo 2000 Nathan Varney Motorsports Photography

  Mustangsandmore.com Forums
  '64 1/2 to '73 -- The Classic Mustang
  vacuum advance

Post New Topic  Post A Reply
profile | register | preferences | faq | search

UBBFriend: Email This Page to Someone! next newest topic | next oldest topic
Author Topic:   vacuum advance
craigber
New to M&M

Posts: 14
From:Vancouver, Canada
Registered: Sep 2000

posted 09-27-2000 11:26 AM     Click Here to See the Profile for craigber   Click Here to Email craigber     Edit/Delete Message   Reply w/Quote
Hi again,

another question about vacuum advance...my rebuilt 351c is running fine and timed to 6 btdc...if I then hook up the vacuum advance my ignition timing go thru the roof (>35 degrees)...I was told to just leave it unhooked and plug the line as it doen't do much anyway but I was also told it could affect my mileage and emissions (we have to pass a yearly test in Vancouver)...this is the second rebuilt distributor I have tried as the first one did the same thing...it is a single diaphram Autolite, single points...I did the Petronix thing once but it crapped out on me after a year and stranded me in a dangerous traffice situation...can I adjust the vacuum advance on the autolight or should I get an adjustable unit? any help is greatly appreciated as this is one of those things that has been nagging me for weeks now...ps the original distributor was traded in for the core charge....thanks in advance (pun intended)

------------------
Craigber
71 Red Rag

IP: 137.82.136.70

Scott (69Mach)
Esteemed Member

Posts: 197
From:Walnut Creek, CA USA
Registered: Jun 99

posted 09-27-2000 02:17 PM     Click Here to See the Profile for Scott (69Mach)   Click Here to Email Scott (69Mach)     Edit/Delete Message   Reply w/Quote
I'm a mechanical distributor guy so I'm not much help. However, I do know that there are different vacuum ports on the manifold. Some that are meant for vacuum advance and some that aren't. Unfortunately, I don't know which are which. Anyone out there have a clue???

IP: 157.22.247.18

craigber
New to M&M

Posts: 14
From:Vancouver, Canada
Registered: Sep 2000

posted 09-27-2000 04:39 PM     Click Here to See the Profile for craigber   Click Here to Email craigber     Edit/Delete Message   Reply w/Quote
Hi Scott,

my vacuum advance is hooked into the carb...under acceleration it is supposed to advance my timing but as mentioned it does so (in a big way) at idle...I don't seem to have any problem off the line so I am assuming my mechanical advance is soft in that it is coming in early...does this sound right??

------------------
Craigber
71 Red Rag

IP: 137.82.136.70

steve'66
Esteemed Member

Posts: 865
From:Sonoma,CA,USA
Registered: Mar 2000

posted 09-27-2000 04:53 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Craig,

If you remove the plate that the points attach to, you'll see the mechanical advance weights and springs. These are attached to a peice that includes the cam that opens and closes your points. There's a clip in the top of the cam that holds this unit onto the distributor's shaft. If you take this off the shaft remove it, and replace it 180 degrees out, you'll probably be on a shorter advance curve. (your firing order will be 180 out too, so either move the wires around on the cap or remove the distributor and replace it 180 out) There's a slot on each side of this part that control how much the mechanical advance can travel. My guess is that your mechanical advance is advancing about 30 degrees all by itself and that it is on the long slot. The shorter slot will limit the mechanical advance and allow you to add some vac. advance. Check it out Our "rebuilt" distributor advances about 34 degrees mechanically (without vac connected) We run it mechanical only and are not worried about a smog test. Good luck, and I hope I explained it good enough

SteveW

IP: 205.188.198.152

craigber
New to M&M

Posts: 14
From:Vancouver, Canada
Registered: Sep 2000

posted 09-27-2000 05:02 PM     Click Here to See the Profile for craigber   Click Here to Email craigber     Edit/Delete Message   Reply w/Quote
thanks Steve,

i will try it this weekend and let you know...can I actually see the two slots...this would allow me to determine if the slots are wrong and need to be changed...do you feel the lack of vacuum will affect a smog test???


------------------
Craigber
71 Red Rag

IP: 137.82.136.70

steve'66
Esteemed Member

Posts: 865
From:Sonoma,CA,USA
Registered: Mar 2000

posted 09-27-2000 05:09 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Craig,

I don't know how they test in your area, but they probably want it to be as it came from the factory. You might get away with plugging up the vac. hose and connecting it for looks Most of the performance guys run straight mechanical advance. Vacuum advance has it's place on a street car for sensing subtle changes in engine load (like going up a hill) while the mechanical advance only responds to engine rpm. For drag racing we don't encounter too many hills or part throttle driving for that matter. Good luck, I'll be racing this weekend but the rest of the gang will be here for you.

SteveW

IP: 205.188.198.152

cpmaverick
Forum Kahuna

Posts: 282
From:AUburn, AL
Registered: Jan 2000

posted 09-27-2000 08:25 PM     Click Here to See the Profile for cpmaverick   Click Here to Email cpmaverick     Edit/Delete Message   Reply w/Quote
Vacuum advance needs a vacuum port ABOVE the throttle plates, at idle it should have almost no vacuum so I am assuming that you have the wrong vacuum port used.

When the throttle plates open, the vacuum from the intake enters the carb and vacuum advance is triggered. When they close the intake is almost sealed off and vacuum advance shuts off.

You can see that if you have it backwards you'll have lots of advance at idle and it'll back off with throttle opening.

If you have a Holley hook it to the metering block vacuum source.

BTW, you can usually adjust vacuum advances by inserting an allen wrench through the vacuum port, but it should already be calibrated for your application.

------------------
-Charlie Ping
1970 Maverick Grabber
-1987 5.0L B303 roller cam/rockers
-1968 Mustang Toploader
-1977 Lincoln Versailles 9 inch w/discs
-1980 Granada Front Discs
www.MAVERICKGRABBER.com

IP: 172.175.211.49

craigber
New to M&M

Posts: 14
From:Vancouver, Canada
Registered: Sep 2000

posted 09-28-2000 12:43 PM     Click Here to See the Profile for craigber   Click Here to Email craigber     Edit/Delete Message   Reply w/Quote
thanks,
I will try to adjust the vacuum advance first with an allen wrench....I suspect the rebuilt distributor was never adjusted...any idea of how much my total vacuum advance should be???

------------------
Craigber
71 Red Rag

IP: 137.82.136.70

cpmaverick
Forum Kahuna

Posts: 282
From:AUburn, AL
Registered: Jan 2000

posted 09-28-2000 01:00 PM     Click Here to See the Profile for cpmaverick   Click Here to Email cpmaverick     Edit/Delete Message   Reply w/Quote
It idle, it should be zero, or close to it.

It doesn't sound like an adjustment problem to me, its way too far off. You should have little or no vacuum at the hose at idle.

If you're sure you have the hose hooked up right, I guess its possible that a big cam or something is causing your carb to have to have the plates open pretty wide at idle. In that case you'll probably need mechanical advance.

I have vacuum advance on my 302 with a B303 cam & Holley 600 DP with no problems.

Anyway, good luck!

[This message has been edited by cpmaverick (edited 09-28-2000).]

IP: 131.204.6.112

bossman
New to M&M

Posts: 63
From:Moreno Valley, CA, USA
Registered: Jun 2000

posted 09-28-2000 01:06 PM     Click Here to See the Profile for bossman   Click Here to Email bossman     Edit/Delete Message   Reply w/Quote
How picky are your emissions inspections? I know before California came out with the 73 and before exemption status, they did a "visual". In that, your car should have a dual advance (retard and advance) vacuum canister along with a thermostatic switch mounted on the water neck (I believe). Check first with them on how picky they are about "correctness" under the hood before you go modifying anything. If everything is cool, Steve has the right idea. I don't run any vaccum advance on my Boss 302 and it is good up to 7500 rpm, with a Pertronix installed. Sorry to hear yours crapped out. Mine has been on the Boss over 10 years when they used to be known as Perlux.

Randy aka the bossman

IP: 206.132.122.54

craigber
New to M&M

Posts: 14
From:Vancouver, Canada
Registered: Sep 2000

posted 09-28-2000 05:18 PM     Click Here to See the Profile for craigber   Click Here to Email craigber     Edit/Delete Message   Reply w/Quote
Hi,

in Vancouver we have yearly emissions tests where they put your car on a "dyno" and stick a probe up its tailpipe...I only have to meet the emissions standards which were in force in 1971 and have previously passed with flying colours...I want to put a 4V carb and intake on soon and thus want everything to work as good as I can...I have a Summit K5201 cam (not too big 218/228) and Crane rockers...for some reason I am getting a lot of vacuum at idle...any more thoughts....

ps. this is the BEST site for Fords I have come across, other sites typically say "yeah, go try it..."

IP: 137.82.136.70

All times are ET (US)

next newest topic | next oldest topic

Administrative Options: Close Topic | Archive/Move | Delete Topic
Post New Topic  Post A Reply
Hop to:

Contact Us | Mustangsandmore.com Front Page

Copyright 2000 SBL Enterprises


Ultimate Bulletin Board 5.45c

EAP 234x60

[Classified Ads] [Links] [Members' Photos] [M&M's Most Wanted] [Restoration Info][Tech Tips]

[ Technical Articles][Ford Technical Data

[ Mustangsandmore.com Bookstore] [Advertise on Mustangsandmore.com] [Mustangsandmore.com T-Shirts]