Vacuum Advance

[Squirrelly]

I have a Cardone 30-2612 distributor on a 200 cid with a vacuum advance canister that can be adjusted. I happened to start the engine cold and it was at high idle and I measured vacuum and was only getting a reading of about 8 and when it stopped high idle it went to zero. My vacuum advance connection is to the Holley 1940 carburetor not the manifold. Is this the correct set up to affect vacuum advance which might improve my gas mileage which is about 10 to 11 mpg?

 

[Xargon321]

Yes at idle you will not show any vacuum at all when connected to the carb its when the throttle plate is open that it generates vacuum

 

[First Fox]

Wow, if you are truly getting that kind of mileage something is definitely wrong. Unless your 200 is in a dumptruck on which the emergency brake is stuck, you should be getting better than twice that much. I get a consistent 25 MPG with a worn out 200 in my Fairmont with an automatic.

A basic tuneup might yield wonders for you. A carb rebuild and properly curving the distributor and setting the timing should be considered also. These things are pretty cheap to do.

 

[ludwig]

First make sure you are at TDC with the distributor.

Once that is good, move on to the engine vacuum. Your idle vacuum should be at least 18*. You need a vacuum gauge to check this. Disconnect the one of the vacuum hoses below the carb, preferably at the manifold below the carb base. The one to the power brakes or something should work. I have multiple nipples off of a brass block that are plugged. I use one of them.

At idle, disconnect the vacuum advance hose at the distributor and plug it so you don't have a vacuum leak. Now turn the distributor until the vacuum rises to 18" or more. Usually it will be counter-clockwise. Do it to the point where you have a minimum 18" of vacuum or as close to that as you can get. Then reconnect the vacuum advance and set the idle in Drive to about 750 rpm when warm.

Once you have done that, make sure the choke is pulling all the way off. If it does not, you need to adjust the choke pulloff.

 

[Squirrelly]

I have had it tuned, retuned and tripled tuned. I changed out the old distributor for a rebuilt one and no change. I had a Pony Carburetor on it and got the same mileage. The car runs great. My son has won 3 trophies at local raceway and it runs about 21 second quarter. It just gets crappy mileage because its all city and I am thinking that the vacuum advance might be the culprit.

 

[FalconSedanDelivery]

It should get a min of 15 -17 with no vac adv , you have other problems

 

[Squirrelly]

I talked to a guy and he is going to rebuild my Holley.

 

[Frankenstang]

Your idle vacuum should be at least 18*.

Just to add to ludwig's estimate...that would be the approximate amt expected when measured at the vacuum fitting on the side of the log.

If you are measuring vacuum at the carb (as you mentioned), and it is a load-o/scv carb the reading will be much smaller, and peak at a relatively low amt (6-7*) max vacuum signal from the vacuum port on a load-o/scv carb IIRC....
EDIT: Apparently closer to 8* max vac signal from an scv carb vacuum port...
(these are distributor rpm based measures, so you have to double them to get total advance)
http://falconfaq.dyndns.org/display1.ph ... Page=9-030

I did not think the load-o vac canister was adjustable, so if you are running a load-o carb/scv carb with a non-load-o dizzy, that will be problematic.

Could be she's just over jetted, jet worn, or too high float setting. Plugs reading lots of carbon (black), would answer that one.
Good luck

 

[Flade99]

1st, make sure you have a carb and dizzy that match. The distributor you have is for a 67 or earlier engine using the Spark Control Valve ported vacuum to control vacuum advance. This is a poor performing system because it does not properly compensate for rpm changes. I.e. it has no mechanical advance. It relies solely on a very weak change in vacuum in the carb to try and measure engine load. There are several versions of the Holley and Autolite 1100 carbs. Pre-68 models have the Spark Control Valve (SCV) required to use your distributor. 68 and later carbs do not have the SCV and must be used with a 68 or later dizzy that has a mechanical advance system in addition to the vacuum advance. This later system performs much better and can be much more accurately tuned for performance and mileage.

2nd, get a Pertronix and replace the points and Condensor. This will give you a much stronger spark and more accurate system. Consider upgrading to their high output coil as well. This will allow you to run a wider spark plug gap increasing performance and fuel economy.

3rd, set the base timing with the vacuum advance disconnected to 10 deg BTDC. With a vacuum gage, connected to a manifold vacuum port adjust the timing to get maximum vacuum. Reconnect the vacuum advance and test drive. Floor the car hard and listen to see if the car knocks. If it does back off the timing 2 degrees at a time until the knocking stops.

4th, retune the carb. Adjust the idle mixture to get maximum vacuum. Turn it in until the vaccuum drops, then turn it back out until the vaccuum no longer increase. The reset the idle speed with the idle stop screw.

Note: all of this assumes you have already ensured you have no vaccum leaks, the cap, rotor, wires, fuel filter, plugs etc are all in good condition.

 

[Squirrelly]

I was talking to my carburetor guy and he said that maybe the intake manifold and spacer might be wrong. I was just reading a post where a guy was getting 10mpg and somebody had rebuilt the engine, like mine was, and put a 250cid intake on it. I need to look at all the numbers. It was rebuilt in 1975 so this could make sense.

 

[Squirrelly]

I don't know if this solves the issue. I have an engine block C6DE-6015-B which is for my 1967 200 but the D5DE-6090-BA intake is for a 1975 200 or 250 cid.

http://forums.vintage-mustang.com/vinta ... mount.html

The post at 03-02-2011, 11:29 PM by 66Sprint200M says that the diameter was larger on the older intakes. I looked it up and I have a D5DE-6090-BA which in 1975 they used on both the 200 and 250 cid engines.

As he notes the spacer might be causing the issue.

Can that be the case?

 

[bubba22349]

Do you have a way of posting pictures of the parts you using? As far as the head code would make it a 1975 head and there is no differance between a 1975 - 200 or 250 head. Oposite the Early heads had a smaller carb mounting hole on the intake, the later model heads had the bigger mounting. Dose your carb mounting match the hole size of the intake? Are you using the correct gaskets for the carb adapter to head and the carb base? Lastly dose your carb have the SCV that you need for the LOD distribitor you are using? Again some pictures of the parts you are using together would really help.

 

[Squirrelly]

I talked to Mike at Classic Inline and he thinks that because they used a larger intake with a bigger chamber when they replaced the head, they needed to mill the head to create the correct compression ratio. If they didn't then he thinks that's my problem. I am going to do a cranking compression test to verify where I am in the range of 155 - 195 to validate his theory.