Vacuum advance problem - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Hotrodding Basics
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 02-29-2012, 08:17 PM
Registered User
 
Join Date: Feb 2012
Posts: 1
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Vacuum advance problem

Hello everyone, i have a problem i was hoping someone could help me out with. I just purchased a 1970 chevy c10 with a 350. Only mod done to the engine is a holley 600 carb. I just purchased the truck so i dont know many of the specs on it. But here is my problem, the truck was running great however i am getting horrible gas milage, i know its not a prius but im getting around 5-7 MPG. So a friend said he just had the same problem and his was that the vacuum advance was connected to a ported vacuum rather than a manifold vacuum. Well mine is the same way so i moved my vacuum advance to a manifold vacuum port and now the truck stutters real bad like it doesnt want to run at all. It will idle but doesnt want to drive very well. If anybody has an idea please let me know. Thanks in advance.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 02-29-2012, 08:48 PM
DoubleVision's Avatar
Not Considered a Senior Member
 
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 40
Posts: 10,655
Wiki Edits: 0

Thanks: 15
Thanked 59 Times in 56 Posts
First off, you should never make changes to the timing via vacuum or mechanical if you don't have a timing light to check the spark timing. Whoever timed it before you could have the timing set where it needed to be and when you connected the vacuum advance to a manifold source now the timing is over advanced which can cause the issue your having.
When you connected the vac advance to the manifold source did the engine idle up? If not then it's likely the vac canister is ruptured internally causing a vacuum leak that is noticeable when connected to a manifold source. When it's connected to a ported source it's not so noticeable. So first things first, get a timing light, then test the vacuum advance unit, if it's ruptured get a replacement. Afterwards, you'll want to disconnect the vac advance and plug it. Set the base timing to 12 degrees before top dead center. Lock distributor. Reconnect vac advance, recheck timing, it should be 18 to 24 degrees before top dead center. My next question is you said the engine was stock besides having a holley carb on it. So I'm taking a guess the intake is stock and there's a adapter plate on it? If so that's likely causing the rest of the issue such as horrible mileage and drivability problems. If it does have a adapter plate you have two options, get a aftermarket intake such as a Edelbrock performer or the like, or get a Rochester Quadrajet to go on it which is what I would do. The Quadrajets small primaries make for excellant low end torque development, throttle response and fuel economy. Another area to why it's using alot of fuel could also be partially due to the ignition system. What shape is the ignition system in? Are you still running points or has it been converted over to HEI? If it has points I would get a points to solid state conversion kit from pertronix. Are the plug wires cheapy parts store wires? If so I would replace them with spiral core wires which last twice as long and have far lower resistance plus better sparking power than the cheap parts store solid core wires. There are other areas you can also improve to get better mileage. If you should want to know just ask.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 10-02-2012, 03:10 PM
Registered User
 
Last photo:
Join Date: Oct 2012
Posts: 5
Wiki Edits: 0

Thanks: 2
Thanked 0 Times in 0 Posts
a little more info here please!

"When you connected the vac advance to the manifold source did the engine idle up? If not then it's likely the vac canister is ruptured internally causing a vacuum leak that is noticeable when connected to a manifold source. When it's connected to a ported source it's not so noticeable. So first things first, get a timing light, then test the vacuum advance unit, if it's ruptured get a replacement."



While reading here about the ruptured diaphram it dawned on me that my vac can really has no function. I have set and reset the timing on my bare bones 350 and ported and manifold vac does the same thing. Dosent really change my timing. That being said, i removed the vac can and applied or tried to apply vaccume presure using a mighty vac tool and i can not get any presure to hold in the can. Translating to no movement of the adjusting rod. Is this a good method for checking these cans?

Question 2 is, I have read that these cans can be adjusted with an allen wrench. Is this true for stock factory made cans? The one i just removed does not appear to be adjustable in any way.
This is all new to me and i have been head scrathing since i started tinkering with this car! So needless to say any and all help will be greatly appreciated.

Mike
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 10-03-2012, 04:24 AM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
holleys typically come jetted rich. Check the size of the front jets and get some jets 2 and 3 sizes smaller for testing.

I would also recommend that you buy an adjustable vacuum advance canister. summit racing sales them for 25.00.

Set the the idle timing to 20 degrees, this should give you about 38 to 40 total revving at 4000 rpm. Verify this!

Then use the adjustable vacuum advance on the manifold source with 10 more degrees of timing. When you plug it in, it should be at 30 degree at idle and around 50 when you rev it in park.

Then, adjust the idle speed to 800 rpms, and then adjust the idle air mixture screws for highest rpm.

You should be getting 10-11 mpg in town and 15-17 on the highway (depending on speed).
Reply With Quote Quick reply to this message
The Following User Says Thank You to 454C10 For This Useful Post:
My 39 Buick (10-04-2012)
  #5 (permalink)  
Old 10-03-2012, 09:28 AM
AZDoug's Avatar
Registered User
 
Last photo:
Join Date: Apr 2010
Location: Camp Verde, AZ
Posts: 62
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Read this.

Doug

http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf
Reply With Quote Quick reply to this message
The Following User Says Thank You to AZDoug For This Useful Post:
My 39 Buick (10-04-2012)
  #6 (permalink)  
Old 10-03-2012, 12:17 PM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by My 39 Buick View Post
While reading here about the ruptured diaphram it dawned on me that my vac can really has no function. I have set and reset the timing on my bare bones 350 and ported and manifold vac does the same thing. Dosent really change my timing. That being said, i removed the vac can and applied or tried to apply vaccume presure using a mighty vac tool and i can not get any presure to hold in the can. Translating to no movement of the adjusting rod. Is this a good method for checking these cans?
That's a good way to test it and it is telling you the can's no good if it won't hold vacuum.

Crane has an adjustable vacuum advance can kit- p/n 99600-1 that has the limiter plate, springs and an adjustable vacuum advance can including tool.

Quote:
Question 2 is, I have read that these cans can be adjusted with an allen wrench. Is this true for stock factory made cans? The one i just removed does not appear to be adjustable in any way.
This is all new to me and i have been head scrathing since i started tinkering with this car! So needless to say any and all help will be greatly appreciated.

Mike
Most adjustable vacuum cans will have a hex-shaped end where the vacuum port is located. Non adjustable cans are round.



More on timing can be seen here.

Until you get a timing light on it, put the line back the way it was. The link above has info on making a timing tape if you don't have a dial back timing light along w/other links at the bottom of the page.

Good luck.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 10-04-2012, 12:26 PM
Registered User
 
Last photo:
Join Date: Oct 2012
Posts: 5
Wiki Edits: 0

Thanks: 2
Thanked 0 Times in 0 Posts
Outstanding, I now know i am on the right track! My new Crane can arrived and has been installed. All of the help is greatly appreciated. I now have to tackle the carb and see if i can get it in line with this motor! Thanks again for all the help!
Reply With Quote Quick reply to this message

Recent Hotrodding Basics posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Opinions on ported of full vacuum for vacuum advance ? y2k600f4 Engine 15 10-07-2011 09:38 PM
Timing... vacuum or no vacuum advance? 454ChevelleMalibu Engine 18 04-25-2010 09:37 PM
ok to use same vacuum line for vacuum advance and tranny vacuum modulator? brian400ex Engine 4 02-19-2003 02:25 PM
vacuum advance problem tonylsg Engine 10 12-13-2002 08:32 AM
computer advance or vacuum advance?? 1984camaroZ28 Engine 1 10-12-2002 02:57 PM


All times are GMT -6. The time now is 10:51 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.