Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - vacuum advance for fuel mileage?
View Single Post
  #9 (permalink)  
Old 09-02-2012, 03:42 PM
LEROYDOZOIS LEROYDOZOIS is offline
Registered User
 
Last photo:
Join Date: Oct 2011
Location: LAKE HAVASU CITY
Age: 22
Posts: 167
Wiki Edits: 0

Thanks: 27
Thanked 1 Time in 1 Post
Quote:
Originally Posted by DoubleVision View Post
So now this goes back to your other thread where I asked where your timing was set. Was vacuum advance in use? Was it connected to a manifold source? You never did tell me what the timing was set at, other than you saying somebody else said it was okay. The base timing should be 12 degrees before top dead center with vacuum advance disconnected and plugged. After it's set lock the distributor. Connect the vacuum advance to a manifold or full time vacuum source (one that pulls vacuum full time including idle)
Now recheck the timing, it should be 18 to 24 degrees before top dead center. When you connect the vac advance right away it's going to idle up.
This enables you to further lower the idle speed, placing the butterflies back on the idle slots on the carb.
As the other guys have said vacuum advance is very important from a mileage stand point. It's also very important in relation to other things such as idle quality, idle speed, and yes without it in use the engine will run hotter and in some cases run hot. Many have asked what use vacuum advance at idle? There are several reasons, one of those is idle and off idle mixtures, such as at cruise speeds the mixture is lean. Lean mixtures burn slower than do richer ones. Due to lean mixtures burning slower more timing advance is needed. Another reason is try and set the base timing at 24 degrees without the aide of vacuum advance, kick back, starter dragging with broke starters will result as there is no vacuum when trying to start the engine so the engine only "sees" 12 degrees before top dead center until it starts.
with the base timing at 12 degrees or lower without vacuum advance another side symptom is poor throttle response. You can have a nice small block with excellant components to make lots of low end torque and without the correct spark advance it will be a powerless slug that drinks gas. I've been down this road several times and that's how I got to where I am now. I was told and I learned. It taught me my brother is right, there is no substitute for experience.
thankyou for the detailed response =] when i get the suburban back ill make sure i go through the steps you wrote above. and i might just hook the vac adv to the port on the manifold so theres no issues as to what its hooked up to on the carb. hopefully ill get the quadrajet working so i can use it instead of the eddy. but ill do the tuning with the eddy being i know it works flawlessly atm.
Reply With Quote