vacum check clarification
#1
Ok guys, i could use your expertise. The past weekend i was doing some tinkering in the engine bay and found a bad gasket between my carb and intake. I thought the car was running good but seemed to lack some giddy up. I fixed the gasket and had to re tune the carb and idle rpm. Now i can spin the tiresBiggrin but i still think i can get it to run better. Or i should say i want to recheck everything from the timing to tuning to make sure all is ok.
So i did some research on the net about tuning and vacum gauge kept coming up. I went to the auto store and picked one up and i also got a digital timing gun that gives me rpm's also.
So i am asking if you could give me a run down for dummies on how to use the vacum gauge for tuning along with timing and how to read the vacum gauge.
I attached a pic of my carb set up as i am not sure on which hose i need to hook the vac gauge up to.
I have one that goes to the pcv valve, one to the front of the distributor, and one to the top of the distributor.
So help a dummy out to make sure he is getting the most out of his motor.
Oh, i have an edelbrock 1406 carb.
[Image: setup.jpg]
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#2
run the mixture screws in all the way , do not crank down on them just snug and then turn out 2 full turns each Hook up your vacuum guage to the intake manifold port of the carb (sucks at idle).
Set you rpm around 500 - 550 rpms ( too high of an idle and you bypass the idle circuit ) then adjust the mixture screws to obtain the highest vacuum reading on the gauge , then readjust idle to normal .
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#3
Do a reading before you do anything and then see what the difference is after fine tuning.

Let us know how it all goes.
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#4
I hooked up the gauge before i did what Thunder suggested and it was right at 16 with my 800 idle rpm.

I turned the IMS to where Thunder suggested to start and idle was down to 410. Adjusted idle up to 520 and started playing with the IMS. Vacuming went up and idle speed did too. The Highest i could get was 18.5 and that ended up around 740 rpms. I readjusted idle rpms to 800 and let her idle for awhile watching the gauge. Never saw the needle blip. I slowly revved it up to about 2800rpms and the needle didn't go over 19.5. I am not sure if it is suppose to move or not.
So it looked like i was close by sound and feel when i first did it.

Did i miss anything?
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#5
You have pretty much done the job. The only thing I would suggest is to back out each IMS about 1/8 to 1/4, turn each. Which will make it a little easier to restart when hot, and reduce bogging when stepping on the throttle. This is from "personal experience" When you get the absolute highest idle and highest vacumn you are at the leanest point, that will allow the engine to run without trailing off/ running lean. Backing them out 1/8 to 1/4 richens the idle mixture slightly and creates better driveability. JTS 71 Mach1
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