• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

24in of vacuum at idle too high for the 2.8L?


SgtDan94

Member
Joined
Mar 7, 2020
Messages
54
Reaction score
2
Points
8
Location
NorCal
Vehicle Year
1984
Make / Model
Ford Bronco II
Transmission
Manual
I did some research on how to adjust the 2150 carburetor on my 1984 Bronco II using a vacuum gauge. Every where I read, they said 18-20in of vacuum is normal for a healthy V6...

I was able to pull 24-25in stable on the gauge while idling at a normal RPM.... is this ok??

I would like to add that the curb idle screw is ALL THE WAY backed out and it’s idling just fine.. normal.

I know that In general you should aim for the highest possible vacuum pressure but 24-25 seems over and above what anyone else is getting. I installed a T in one of the vacuum lines coming off the manifold tree for my vacuum gauge.

My bronco has 150,000mi and is in very good shape, probably driven lightly for most of its life. I’m planning on just leaving it this way.. unless this high of vacuum pressure is a bad thing.
 


Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,704
Reaction score
13,160
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
It could be that your vacuum gauge is off... not calibrated. If you don't have idling issues... or drivability symptoms... I wouldn't worry about it. Maybe check another vehicle with your gauge and see what it shows.

I know these to have an idle speed screw and a fast idle speed screw. The terminology may differ depending on who you're talking to. Idle speed screw would contact the throttle lever and the fast idle speed screw will contact the fast idle cam... which is part of the choke system. If you can back the idle speed screw all the way off and it is not contacting the throttle lever... and the engine still runs... you may have bent throttle shaft or the shaft bushings are worn. Does the throttle shaft have movement in the shaft bore? Did you remove the throttle plates from the shaft?
 

SgtDan94

Member
Joined
Mar 7, 2020
Messages
54
Reaction score
2
Points
8
Location
NorCal
Vehicle Year
1984
Make / Model
Ford Bronco II
Transmission
Manual
It could be that your vacuum gauge is off... not calibrated. If you don't have idling issues... or drivability symptoms... I wouldn't worry about it. Maybe check another vehicle with your gauge and see what it shows.

I know these to have an idle speed screw and a fast idle speed screw. The terminology may differ depending on who you're talking to. Idle speed screw would contact the throttle lever and the fast idle speed screw will contact the fast idle cam... which is part of the choke system. If you can back the idle speed screw all the way off and it is not contacting the throttle lever... and the engine still runs... you may have bent throttle shaft or the shaft bushings are worn. Does the throttle shaft have movement in the shaft bore? Did you remove the throttle plates from the shaft?
I did not remove the plates and the shaft does not have play. It’s possible that someone else did?? Should the throttle make contact with the tab that the idle screw threads into.. with the screw all the way out? Because it doesn’t..

It idles and drives ok. I don’t have a tachometer installed, though I plan to install one (posted a different thread about it). It idles pretty low and seems to run smooth.

Here’s the thing.... I got this bronco a few days ago and it wasn’t running, the previous owner said “it needs a new carb.” Instead, I took the existing carb off, a motorcraft that was remanufactured by Holley probably back in the 90s, since this Bronco was last registered in 1997. The carb looked clean inside... like it didn’t need a rebuild and instead just needed to be calibrated. So I reset the mixture pins to 1 1/2 turns out, and I had to turn IN the WARM idle screw in order for the engine to idle with pins at 1 1/2 turns....

From there, I adjusted the pins until the vacuum reached 24in... it wouldn’t pass 24in, but had a steady/ stable needle. I then proceeded to turn the idle down... I ended up unscrewing the idle screw (on the drive side) all the way and it just so happen to sound correct (by ear) once it was all the way out.

to be clear, the tab that the “warm idle” screw threads into... the throttle doesn’t come into contact with this tab when the screws all the way out... I don’t know if it’s supposed to, but there’s about a quarter inch of space in between
 
Last edited:

Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,704
Reaction score
13,160
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
I'm confused with the term warm idle pin... what is that?
 

SgtDan94

Member
Joined
Mar 7, 2020
Messages
54
Reaction score
2
Points
8
Location
NorCal
Vehicle Year
1984
Make / Model
Ford Bronco II
Transmission
Manual
I'm confused with the term warm idle pin... what is that?
I corrected “pin” for screw.. I’m referring to the idle adjusting screw on the driver side. The screw you would adjust once the engine is at operating temperature. Not the fast idle screw. I understand the fast idle screw is only relevant while the choke is engaged.
 

Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,704
Reaction score
13,160
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
It's probably normal for there to be a gap if the idle speed screw is backed out all the way. Again... I wouldn't worry to much about that... unless the idle speed is way to fast. Or if you can physically close the throttle more... in that case I would put a return spring on the throttle.

It sounds like you're on the right track...

I would try putting some miles on it... adjust as necessary. You may have to tinker with it a bit to get it right.
 

SgtDan94

Member
Joined
Mar 7, 2020
Messages
54
Reaction score
2
Points
8
Location
NorCal
Vehicle Year
1984
Make / Model
Ford Bronco II
Transmission
Manual
It's probably normal for there to be a gap if the idle speed screw is backed out all the way. Again... I wouldn't worry to much about that... unless the idle speed is way to fast. Or if you can physically close the throttle more... in that case I would put a return spring on the throttle.

It sounds like you're on the right track...

I would try putting some miles on it... adjust as necessary. You may have to tinker with it a bit to get it right.
Im getting a SMOG pretty soon here. Im interested in seeing the results. I have little experience with carburetors so I would like to see if I at least came close to calibrating it’s correctly.

honestly, I think the idle can be increased a little bit.. I’ll know once I figure out how to get the tach installed.
 

Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,704
Reaction score
13,160
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
Idle is always the dirtiest... the lower it idles the worse it gets. Running a few extra rpms during a smog test will not hurt you one bit. Just as long as it doesn't exceed the idle speed thresholds of the test.
 

alwaysFlOoReD

Forum Staff Member
TRS Forum Moderator
TRS Banner 2012-2015
TRS 20th Anniversary
Joined
Apr 13, 2009
Messages
13,870
Reaction score
5,030
Points
113
Location
Calgary, Canada
Vehicle Year
'91, '80, '06
Make / Model
Ford, GMC,Dodge
Engine Size
4.0,4.0,5.7
Transmission
Manual
2WD / 4WD
4WD
Having a small vacuum leak can help smog too.
 

SgtDan94

Member
Joined
Mar 7, 2020
Messages
54
Reaction score
2
Points
8
Location
NorCal
Vehicle Year
1984
Make / Model
Ford Bronco II
Transmission
Manual
Having a small vacuum leak can help smog too.
Idle is always the dirtiest... the lower it idles the worse it gets. Running a few extra rpms during a smog test will not hurt you one bit. Just as long as it doesn't exceed the idle speed thresholds of the test.
Speaking of vacuum leak.. There’s a vacuum line that stubs up within the intake.. and within the circular air filter, beside the circle cutout for the carburetor. Should this have something attached to it? (See attached)
 

Attachments

Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,704
Reaction score
13,160
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
It's been to many years since I've looked at one of these... I think that might be a thermo switch for the air pre heat door in the snorkel. I don't believe there is anything connected to it from the inside. @19Walt93 worked with these and has a super memory... he might know for sure.

As for the truck being prewired for a tach... I'm not sure about that. I kinda thought a tach was standard equipment with a manual transmission. Tach hook up is pretty basic... power, ground, illumination and negative side of the ignition coil.
 

8thTon

Well-Known Member
--- Banned ---
Joined
Jan 13, 2019
Messages
1,378
Reaction score
806
Points
113
Location
Pennsylvania
Vehicle Year
2004
Make / Model
Ford
Engine Type
3.0 V6
Engine Size
3.0
Transmission
Automatic
2WD / 4WD
2WD
My credo
My world is filled with stuff that needs to be fixed
Your throttle plates should not be closing so far that they bind in the throttle bores, they are supposed to hit a mechanical stop (idle speed adjust). If your idle is too high then you likely have a vacuum leak somewhere. If it's small you may be able to tune it in terms of mixture, but it will still add air and increase idle.

Sometimes a hot idle device is added, which is a small bimetal thermostatically activated air leak intended to increase idle speed on hot engines. This could be mounted in the air filter housing. It looks like what I'm seeing in your picture, but it's hard to tell. If that has failed open then it would be your high idle problem. Plug it and see what happens, it's no big deal to run without it for a while. If you plug it disconnect the hose and plug it at the line, covering that exposed tube won't work.

A larger tube may run into the air filter which could be the fuel bowl vent. That would not have anything on it.
 

19Walt93

Well-Known Member
Ford Technician
V8 Engine Swap
Joined
Nov 13, 2018
Messages
4,475
Reaction score
4,412
Points
113
Location
Canaan,NH
Vehicle Year
1993
Make / Model
Ford Ranger
Engine Type
V8
Engine Size
351
Transmission
Automatic
2WD / 4WD
2WD
Total Drop
3"
Tire Size
235/55R16
My credo
If you don't have time to do it right will you have time to do it over?
The hot idle compensator isn't in the air cleaner, it would mount to the back of the carb. The piece in the air filter shouldn't be capped. Vacuum should feed one side of the vacuum valve and the other side would connect to the air cleaner vacuum motor that allows warm air to be drawn into the air cleaner during warm up.
 

Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,704
Reaction score
13,160
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
I kinda thought that is what it is... Thanks for the clarification Walt.
 

Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,704
Reaction score
13,160
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
@SgtDan94 ...

Something else I noticed in your picture... The air cleaner snorkel is missing the flexible coupler between the air cleaner and the cold air intake. This would allow heated air in the engine compartment to be drawn into the air cleaner opposed to drawing in fresh air from the front of the vehicle. You should look into sourcing one of those...
 

Sponsored Ad


Sponsored Ad

Staff online

Member & Vendor Upgrades

For a small yearly donation, you can support this forum and receive a 'Supporting Member' banner, or become a 'Supporting Vendor' and promote your products here. Click the banner to find out how.

Truck of The Month


Kirby N.
March Truck of The Month

Recently Featured

Want to see your truck here? Share your photos and details in the forum.

Follow TRS On Instagram

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store


Sponsored Ad


Sponsored Ad

Sponsored Ad


Amazon Deals

Top