[CrossHair]

Hi, after I messed my CJ up by putting Diesal in there I've been trying to get it all tuned back in etc.... Well someone had mentioned how you use a vacuum gauge to set fuel/air mixture on the carb. I went to autozone but the one he showed me looked almost like a whole kit. It seemed overkill, hoping you can help me out with a suggestion... and maybe even how to use it. Thanks.
Ken

[John Strenk]

If your carb is out you vacuum will drift around. you adjust it to stop wandering and get the highest reading.

Here is a cool site.
http://www.secondchancegarage.com/public/186.cfm

Mine looks like this:


I also have one in my jeep:

[Fjguercio]

I got the one at Advance Auto, complete kit also and nice quality. The kit will have the 3-4 adapters so you can tie into you vaccum system. Looks very similar to what John posted above. Was $24 approx large face and connections, directions are ok also.

Fred

[LSUtiger]

I got mine from sears. http://www.sears.com/shc/s/p_10153_12605_00971099000P?keyword=vacuum+guage

[CrossHair]

Cool I'm glad I asked cuz they wanted $49. I have an Edelbrock, I'll check that site out but am I just to hook it to one of the front ports and adjust the air to fuel mixture screw till the highest reading then back off 1 inch pound or something? And John you always have yours connected huh? Thanks,
Ken

[John Strenk]

Originally Posted by CrossHair

Cool I'm glad I asked cuz they wanted $49. I have an Edelbrock, I'll check that site out but am I just to hook it to one of the front ports and adjust the air to fuel mixture screw till the highest reading then back off 1 inch pound or something? And John you always have yours connected huh? Thanks,
Ken

That sounds more like setting your timing with a vacuum gauge. When adjusting the mixture, I always leave mine set at the highest vacuum setting.

Yeah I have mine on all the time. A lot more action out of a vacuum gauge when driving. It helps your driving style if you're trying to get the best gas milage.

[crusty75]

John, I just had a friend give me a vacuum gauge from an old Scout for my 75/5. I use one to tune, but I'm ignorant in how to use one mounted in the vehicle to attain best gas mileage. Being an old coot with a fixed income, this gas mileage thing is becoming very important. Could you let us know how to interpret an in cab gauge for best mileage?

I remember years ago I had a rich friend in high school who's dad gave him a brand new '63 Grand Prix Pontiac 389 tri power for his 16th. It had a vacuum gauge in the console with a green area marked "economy", but it has been so long, I can't remember in more detail what that range was in inches of vacuum. All I remember was that at .25 a gallon, and three two barrel carbs, it was a bad thing to be in the green "economy" zone. Sadly, things have changed.

[Mr.Crowley]

the higher the vacuum Lb.s the better the gas milage..Mainly when cruising with very little pettle..The engine is operating at or nere peek performance when the vac is high with a load..

[xxxflhrci]

Originally Posted by crusty75

I remember years ago I had a rich friend in high school who's dad gave him a brand new '63 Grand Prix Pontiac 389 tri power for his 16th. It had a vacuum gauge in the console with a green area marked "economy", but it has been so long, I can't remember in more detail what that range was in inches of vacuum. All I remember was that at .25 a gallon, and three two barrel carbs, it was a bad thing to be in the green "economy" zone. Sadly, things have changed.

Yep, I drove a 1966 Plymouth Barracuda in high school with a vacuum gauge labeled "power and economy". It was in the dash where a tach would go.

[John Strenk]

Yep, drive with the highest vacuum you can obtain. Usually I can stay around 10-15 inHg. This is a good way to see were your gas milage goes to heck. If you are driving around at 0-5 inHg and your power valve is set to open at 8 inHg and dump in extra fuel. Well, you're dumping a lot of extra fuel.

Make sure you are connected to manifold vacuum and not ported vacuum.

[crusty75]

Thanks all. Having no flat ground within miles and miles, I have a feeling once I get the thing hooked up, It will get depressing real fast. Oh well, beats living on a pool table. With today's gas prices, I guess there is a reason folks say only poor people live in the mountains. You might have some money when you move here, but not for long!

[JeepHammer]

Wider the face, the easier it is to read...

I have had the same Sears vacuum gauge for about 20 something years and it works fine. Still about $20 the last time I saw one at Sears.

DO NOT get the 'buffered' or liquid filled type!
You want to be able to see fast changes in the vacuum, and liquid filled or buffered will NOT show you small/fast vacuum changes...

Don't use the really soft type of vacuum line, or really long vacuum lines if you can keep from it.

Soft line will 'Buffer' the vacuum by absorbing some of the vacuum changes.
Long lines will have a lot of internal volume, working like a 'Vacuum Reservoir' and will 'buffer' the vacuum signal.

Shorter, stout lines will give you the best, most accurate signal.
I actually will use rubber fuel line (since it has a much stiffer construction) when I'm trying to diagnose something that will have slight or fast needle movements...
Helps keep the vacuum signal from degrading or softening on the way to the gauge.
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Even on flat ground, watching a vacuum gauge when you are driving will teach you how to drive for maximum fuel economy...

Generally, the higher the vacuum reading, the better mileage you are getting.
If you watch a vacuum gauge when driving, you will sure learn to let up on those jack rabbit starts, let off the gas pedal and coast a while before you stop, and leave the throttle at a constant position instead of constantly speeding up and slowing down!
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JOHN!
With a vacuum gauge and a note pad, you can find out EXACTLY what power valve you need!

When you are flat cruising, not moving the throttle pedal, at what ever your normal commute speed or average highway speed is, take note of the vacuum reading.

On average, your 'Power Valve' size should be about 2 In.Hg. below that.
That way, your power valve doesn't pop open when atmospheric pressure changes, slight tipping of the throttle pedal to keep up with traffic, ect.

Off roaders might want to go about 2.5 In.Hg. below the average, so the power valve doesn't open on the trail when you are trying to 'Finesse' the throttle on a tight obstacle.

Highest STEADY vacuum readings at idle (provided both idle mixture screws were moved the same amount out at all times) will be a good thumbnail way to set your idle mixture with a vacuum gauge.

You can get a ball park (not very accurate at all) set to your ignition initial advance also.
Again, once the idle fuel mixture has been set, use the vacuum gauge to find the highest manifold vacuum reading while you adjust the distributor for initial timing.
THIS DOES NOT TAKE THE PLACE OF A TIMING LIGHT!

You can get within about 5° of where you should be, but this is by no means the 'Correct' way to set initial timing!
This is simply a 'Field Expedient' way of setting timing so you can get back to someplace that has a timing light to do it correctly.
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Remember, when you are airing down, an accurate low pressure gauge (0 to 15 PSI) is pretty expensive, and redundant if you have a vacuum/Pressure gauge...
with nothing but a short hose with air chuck you can use your pressure vacuum/pressure gauge for checking those low pressure tires!
Making use of one tool for several different things will save you money, space and time.

Most of the 'Kits' come with enough parts you can also use the vacuum/pressure gauge to diagnose fuel system problems!
Most of the vacuum/Pressure gauges are fuel safe, so you really luck out there!
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Anyone that doesn't know all the things a vacuum gauge can diagnose might want to read here,
http://www.junkyardgenius.com/tools/vacgauge.html