What and Where is a Vaccum Advance?
08-04-2009, 01:04 AM
#1
Thread Starter
Join Date: Jul 2009
Location: Mississippi
Posts: 32
What and Where is a Vaccum Advance?
I hear and read people talking about a "vacuum advance" when referring to bogging problems at WOT. I was hoping someone could tell me where the vacuum advance is on the distributor and how to disconnect it? I'm having a problem of enging not making power at WOT and after WOT, it idles really high. If I cut the car off and back on it's fine for the most part.
EDIT: Also, what is meant by full manifold vacuum.
EDIT: Also, what is meant by full manifold vacuum.
Last edited by Mesomorphman; 08-04-2009 at 01:08 AM.
08-04-2009, 01:11 AM
#2
6th Gear Member
Join Date: Apr 2007
Location: California
Posts: 10,468
I doubt that's vacuum advance related. But the VA uses intake vacuum to increase timing at part throttle, and usuallyt here's a rubber line going from somewhere on the carb(typically a ported vacuum so the advance only works off of idle) to the dizzy. But your problem sounds like the mechanical advance might be sticking, or possibly a throttle linkage/binding issue.
08-04-2009, 01:25 AM
#3
3rd Gear Member
Join Date: Jul 2009
Location: Smyrna, TN
Posts: 678
Hi, if you have the stock dist. the vacuum advance is that silver canister on the front of the dist. with a vacuum hose going to it, other end of the hose goes to your caburator (timed/ported) nipple. You can see it here at the front of my dist. just left of the coil:
Full manifold vacuum is what your brakes and auto trans use and it's usually 17-18 psi on a gauge. Timed/ported vacuum changes with RPM. As your car increases RPM's your timing advances with a proper working system giving more power and mpg. If you have two nipples the timed/ported is usually the higher one on the carb. but if you post your carb make/model we could look it up to make sure you're hooked to the right one. Pretty sure most all Fords used the timed/ported vs. full vac.
Be sure to test your vacuum advance to make sure the diaphragm in it hasn't dried out/cracked after 40+ yrs. (mine was, so my timing wasn't advancing). Remove your dist cap and look for the flat rod that extends from the vacuum adv. and hooks onto a plate in your dist. Now disconnect the vacuum line from your carb and suck on it, you should see that flat rod pull into the advance and moving the plate in the dist. If it doesn't your vac. adv. is bad and causing a vac. leak. You can get replacement from parts stores.
When you set your initial timing you disconnect the vacuum line and plug it.
Jon
Full manifold vacuum is what your brakes and auto trans use and it's usually 17-18 psi on a gauge. Timed/ported vacuum changes with RPM. As your car increases RPM's your timing advances with a proper working system giving more power and mpg. If you have two nipples the timed/ported is usually the higher one on the carb. but if you post your carb make/model we could look it up to make sure you're hooked to the right one. Pretty sure most all Fords used the timed/ported vs. full vac.
Be sure to test your vacuum advance to make sure the diaphragm in it hasn't dried out/cracked after 40+ yrs. (mine was, so my timing wasn't advancing). Remove your dist cap and look for the flat rod that extends from the vacuum adv. and hooks onto a plate in your dist. Now disconnect the vacuum line from your carb and suck on it, you should see that flat rod pull into the advance and moving the plate in the dist. If it doesn't your vac. adv. is bad and causing a vac. leak. You can get replacement from parts stores.
When you set your initial timing you disconnect the vacuum line and plug it.
Jon
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