15 miles per gallon ?

Distributor shouldnt be ran off of straight manifold vacuum. It should come out of the vacuum port on the carb and have no vacumm at idle and increase in vacuum under throttle. It pulls its vacuum from above the throttle plate plate so it only advances when you are higher than idle speed.

 

You can run manifold vacuum to the distributor. Ford did it for years before emmission controls took over. It will allow the engine to stay cooler at idle and idle at a lower speed (which is better for mileage). When accelerating or at wide open throttle there is no difference either way. The only difference is that at idle it will have more advance than with it hooked to the ported vacuum.

 

Thank you Paul, I had been thinking that over at work today. I was wondering why it would make a difference either way. My '70 f-100 was hooked up with a manifold vacuum from the factory also. Good knowledge and wisdom, thank you.

 

My stock '73 Grabber 302, C4,2.79 gear, 2bbl with headers & duals got about 20 driving normally. My Comet with a b303 cammed 302, holley 600, stock C4 and 3.00 gear gets about 17 (it could use some carb tuning, it's a bit rich). Also, the '73 still had the points dizzy, but I did put in the different advance springs in it. You should be able to squeeze 20 with a few mods and some tuning. Going to electronic ignition is ok, but for the money spent you won't see much if any improvement over the old points IF your old dizzy is in good shape and the points set properly. I would go with an earlier timing gear, better advance springs in the dizzy, dual exhaust(headers not really needed)and pump up those front tires to about 35 psi. And learn how to drive more steadily. It all adds up!

 

That makes sense. you would still be setting your initial timing with the vacumm off the dist. and max advance is the same either way. Just thinking at idel it shouldn't be advanced that much. I haven't worked on many stock cars, all the aftermarket carbs I have worked with mention the vacumm should be run off their off idle vacuum.

I wonder if the original stuff worked off manifold vacuum because it went through a thermal operated ported vacuum switch (usually mounted on thermostat housing) that would allow vacuum to the dist. until the engine reached operating temperature?

 

Long before the emission control switches were used all the car makers used manifold vacuum to the distributor. The switch was there to let the timing advance at idle when the engine started to overheat at idle - using manifold vacuum. Engines like a lot of advance when idling. You normally have to turn the idle speed down after you switch to manifold vacuum and lean out the idle adjusters a bit.
Using manifold vacuum is better for your engine than using ported vacuum. Better mileage, better idle and better fuel economy.

 

I was just thinking I should try switching the vacuum ports and see how much faster my timing advances. But then remembered I have an MSD dist. withno vacuum, Might give it a try on my truck, since its a manual and revs up quicker a faster advance curve might be better.

 

Gas Mileage

I get 24.5 on my Town Car on the road.

34 MPG on my 09 Hyundai Sonata Limited TEXAS Edition

I have never checked my 75 Mav 200-6 with auto but it is good.

Texasjack

 

Without reading 3 or 4 pages of replies, yes, that is appropriate, if not low.

I got 20 mpg on a 302 with gt40 heads and edelbrock 600cfm carb, if I kept my foot off of it. With a 3.80 rear gear.

Ride it lightly and you will get good gas mileage.

 

MyMaverick went up to 16.5 just by hooking the vacuum up to a manifold vacuum, but keep in mind that I could'nt get it to pull a vacuum from the port on the carb. base at all. I will install my new distributor and MSD coil by the weekend, and see what benifits that wiil yield. I did put a new fuel pump on it today. I noticed that it was spritzing gas on the oil filter. I have'nt seen it do that before today. I felt fortunate that I did'nt burn up in it, or at least catch the car on fire. I have seen fuel pumps start leaking oil before when then the diaphram goes out, but never gas. To be sure, it had'nt been doing that for long.

 

Hooking your vacuum advance to manifold vacuum doesn't change the timing when you are running except at an idle. As soon as you open the throttle the vacuum advance is the same whether you have it connected to ported vacuum or manifold vacuum. The ONLY difference is that at idle ported vacuum is shut off and going straight to the manifold it isn't. They are both manifold vacuum - ported vacuum is just shut off when the throttle is closed.
It will give you better mileage if you spend a lot of time off the gas but the improved mileage is only when the throttle is closed.

 

I did'nt have a vacuum at all at the the carb base, even when I revved it up with my finger over the vacuum port. So I was running the whole time with no vacuum. My car is a one owner car with everything that came on it from the factory, still under the hood. Every little vacuum hose and port, or line. So in the beginning, I assumed everything was functioning the way it should, until I investigated further.

 

O.k., I have installed my Pertronix distributor and MSD Blaster ll coil, and have been driving it off and on for about two months. My '73 Maverick has gotten as good as 17.75 mpg with just those two modifications. I did put the lightest spring kit that came with the distributor, in it. I drive it the same as I did before the change. It still has the factory single exhaust, cam, and timing chain and gears. As money permits, I will change the cam/lifters. timing chain/gears, and exhaust. I will keep you guys posted on any more progress.