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how much vacume off the manifold should I have . stock 302 2 barrell .

benelibutton

Full Member
Joined
Nov 27, 2012
Messages
326
I have about 18.5 at idol right now. Seems to be running good. And tips on using the vacume gage for tuning the stock carb would be awsome.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Thats about right.18-20 in. is in the range you should be in. As for tuning just looking for the highest steady vacuum reading.
 
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benelibutton

Full Member
Joined
Nov 27, 2012
Messages
326
So ten inches would be ok? I could use a little less idel . And the automatic choke on the side? If its a little hard starting can I adjust it with that
 

ugly74

Bronco abuser
Joined
Apr 17, 2006
Messages
2,847
You want it adjusted for the highest steady vacuum, and after that, you can drop the idle speed back down, using the speed adjustment screw thats at the throttle linkage.

You do not want to find the right idle speed by messing with the mixture (air/fuel ratio) screws.

As for the electric choke on the side...i usually start by adjusting it so that the choke is not quite half closed when the engine is stone cold (a little more than that in winter)

Pump the pedal one time, and try to start it. If all else is good, she should fire up.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,353
So ten inches would be ok?

He said "minimum" so that would not be a good goal to shoot for. At idle you want it right where you have it, or higher if you can get it there without causing other mischief.


I could use a little less idle.

As ugly74 said, you adjust the other stuff, then reset the idle with the idle speed screw. Then you set the idle mixture screws and reset the idle with the idle speed screw. Then you set the timing (again) if needed and reset the idle with the speed screw.
Basically you don't set the idle with the other parameters. You make the other adjustments to where they should be, then match the idle to everything else using the single screw.
Any time you advance timing, you usually gain idle speed, and vise versa.

Setting the idle-air mixture screws and then the idle speed is a little dance that you have to do. One thing changes the other, then you go back and reset the other. Do that in little steps until they all sit where you want them.


And the automatic choke on the side? If its a little hard starting can I adjust it with that

Not the idle speed, but yes, you can sometimes help a hard-starting engine with proper choke adjustments. But there are certain ranges of "correct" here too, and hard starting is not always the choke. It can't hurt to test that theory, but don't overlook ignition timing, point and condenser condition (unless electronic ignition is used?) and spark plug condition. Every one of those will have an effect on starting. Cold and hot.

Good luck.
Oh, and what year is your Bronco?

Paul
 

savage

Contributor
Bronco Nut
Joined
Apr 18, 2007
Messages
2,482
Loc.
Renton
Hey Paul, does the different type of cams affect the vacuum in different ways? Don't radicle cams make it harder to adjust?
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
If its a stock engine then seeing 10in at idle would be bad. Some built engines may only pull 10in at idle but thats usually with a fairly large cam which would not normally be in a bronco to begin with.

Camshafts do affect idle vaccum as some will only allow you to pull only so much no matter what your timing or idle speed is set at. Most cams we use in broncos will pull14-20in. Radical cams will give different vaccum readings so your highest steady reading may no be achieveable but will become highest and steadiest reading you can attain
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,353
Hey Paul, does the different type of cams affect the vacuum in different ways? Don't radicle cams make it harder to adjust?

Yep on both counts.
I suppose it's not really making it "harder to adjust" as much as it is harder to tell when you've got it adjusted. A lopey idle and even some roughness and spitting fuel out the top of the carb and poorer functioning of vacuum accessories like brake boosters from a more radical cam just isn't going to be tuned out in the normal ways.

Paul
 
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benelibutton

Full Member
Joined
Nov 27, 2012
Messages
326
I think I have it pretty steady right now at 18.5 but im still going to turn down the idel a little.
 
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