Thanks BubbaF250. I shifted the canister from the 88 distributor to the dist. I am using now and have found improvement. I have also adjusted my initial timing up some( to 14 BTDC )so far, as suggested in your website. With the 14D, full clockwise vacuum adjustment, and the mech. advance springs changed to get full advance early, I still have no pinging. The power is better but I still get a bit of unburned gas early in acceleration. The fire is good; spark is bright and jumps 1.5" to ground. Would any other canister you know of give me more advance movement?

 

I am running my vacuum advance from the ported vacuum and the manifold vacuum with a "T" to link them. It seems to work fine so far. I have no other vacuum draws than the brake booster.

 

Upon closer inspection after pulling off the carb, I found what appears to be 2 vacuum ports on the intake. One is directly under the EGR (and it was plugged) and the other was over to the right(drivers side) and it is open. What are these? and where do they hook up?

I am looking at the diagrams from autozone but they list part names they don't have pictures of what they are and since I am clueless about what I am looking at I can't figure them out.

Thanks alot guys.

 

315 power,

Disconnect the manifold vacuum source from the T fitting and plug it. Manifold vacuum is distorting the signal from the carb's spark port, which should provide the signal for the vac advance. You may need to retune some more to correct for the change.

When the throttle plates are less than about half wide open, manifold vacuum is much stronger than the ported vacuum, so it causes the manifold to suck fuel/air mixture out through the spark port. That will artificially enrich the cylinders fed by the runner(s) that provide the manifold vacuum, and lean out the mixture in the other cylinders fed by the right side of the carb.

At idle and low throttle openings, manifold vacuum will give too much vacuum to the vac advance. Vac advance will be maxed out at idle.

JoeBlow,

What are the names or abbreviations of the components you need to find?

 

Now I'm confused after reading these posts. I thought that the ported vacuum on the carb's right side under the choke was for the EGR (through a TVS mounted in the manifold) and that the vacuum advance source was the nipple coming from the driver's side front of the carb. I've never been able to find what I consider a "correct" vacuum diagram for my truck ('79 F100 302 auto/AC). Should the EGR and vacuum advance get the same signal? I thought the ported EGR source went off at WOT but that you still wanted a strong vacuum signal to have maximum advance at WOT. Am I wrong?

 

The nipple on the left (driver's side) is called the "E" port, and it is used to trigger the purge control valve for the evaporative emissions system. The Purge CV allows manifold vacuum to purge fuel vapors trapped by the carbon canister (from the fuel bowl vent and fuel tanks) when the engine was turned off.

Some earlier configurations used the "spark" port on the right side of the carb to operate the EGR valve, but that port was designed to provide the signal for the ignition vacuum advance (long before EGR was invented).

Most later EGR configurations (late '70s-up) used a switching valve or vacuum amplifier that passes manifold vacuum to the EGR valve diaphragm, based on a vacuum trigger signal. Some systems still used the spark port for the trigger signal, and some used a dedicated EGR signal port (on left rear of the carb, above the mounting flange). The dedicated EGR signal port originates in the left main venturi, well above the throttle plate.

Ford phased out the earlier systems that used just spark port vacuum for the EGR valve because they didn't allow a strong enough spring in the EGR valve (maximum vacuum from the spark port is only about 10-12 in/Hg).

Later, Ford went to the dedicated EGR signal port because its signal is always directly proportional to airflow through the main venturi, and it is not affected by throttle position.

The spark port signal is (somewhat) proportional to throttle position when the throttle is at or near closed, and it is directly proportional airflow through the throttle bore when the throttle is at or near wide open.

Maximum ignition advance does not occur until the engine runs fast enough to get all of the mechanical (centrifugal) advance, as well as whatever vacuum advance is contributed. That is not directly related to throttle position (i.e., WOT).

 

Bubba, what if I put a check valve between the ported vacuum and the "T" to keep the manifold vacuum from robbing the right side venturi? It seems to need more vacuum to make the vacuum advance canister move enough. I still have not found the right one; the part I think I need is VC 230 from Standard.

 

There are two types of check valves, one-way and two-way. The one-way valve allows air to flow in one direction, but not the other. A two-way check valve allows air to pass in both directions, but restricts the flow rate.

A one-way check valve with a stronger vacuum pulling it closed all the time will have the same effect as disconnecting and capping off the stronger signal.

The function of a two-way check valve is to buffer the effect of rapid changes in the strength of a vacuum signal. Think of it as smoothing out the spikes.

A two-way check valve will slow down the movement of air through the hose from the spark port to the manifold, but it will not keep the stronger vacuum from overpowering the weaker, and the resulting vacuum will always be the stronger of the two sources.

Even with a one-way check valve between the "T" and the spark port (to keep manifold vacuum from sucking air out the spark port), the improvement on vacuum advance would be marginal, if any. Spark port vacuum is usually weaker than manifold vacuum until near WOT. And then, if air can be pulled from the manifold easier than it can be pulled from the vacuum advance, the alternate path created by connecting the manifold vac source will weaken the spark port's signal to the vacuum advance.

Try adjusting the vacuum advance unit's sensitivity so it takes less vacuum to move the advance. If you adjust it to maximum sensitivity, you should get maximum advance with about 6 in/Hg vacuum. If that still doesn't give you enough advance, you need to find a different unit that gives more advance, or one with less spring tension on the diaphragm so you can get maximum advance with less vacuum.

Depending on the performance you're trying to achieve, you might need to adjust the mechanical advance by changing the springs on the weights.

 

I have tried all those ideas you mention except I am still searching for the right vacuum advance canister. I

 

Sorry, I lost my connection. I think once I find the proper canister I should be able to find the right timing. Does the manifold vacuum ever go to 0 ?

 

It is near 0 at WOT.

 

my 85 f150 351 has 89,000 on it..it I have changed wires,plug,dist,battery.alt. and a new carbb basicly everything...I am haveing a hard time starting it and keeping it going cold.Once it warms up it runs ok..
MY question is I have 2 carbon canisters, 1 is not hooked up to anything , the other is.....CAN THIS BE THE CAUSE TO MY HARD COLD STARTING ? I'm not sure where the hoses would go to and from ....BUT i think this is my problem

WHEN I FIRST TRY TO START IT, i have to pump it 20 times, crank it, pump it 10-15 more times crank it, then maybe she'll start, then i have to keep my foot on the gas till she's warm

 

Sounds like a choke problem.

Please start a new thread to discuss this issue.

Don't forget to give some more info like what carb you have and any mods to the engine.

 

if its ported vacum you will only have vacum off idle , good luck,bob