Idle not low enough and rough

Tiny
CJA31186
  • MEMBER
  • 1983 JEEP CJ7
  • 4.2L
  • 6 CYL
  • 4WD
  • MANUAL
  • 111,000 MILES
It has a brand new rebuilt stock BBD carburetor, electric fan, aluminum radiator, aluminum valve cover, and power brake booster. I am unable to get the idle speed set correctly. If I adjust the two mixture screws on the carburetor to get the vehicle to idle lower, it will stall out when stopping or will not start. If I adjust them the other way it will not reach top speed. Right now the best it will run is when I have the idle set at 1100, which keeps it running on cold start and stopping, and allows it to reach top speed. What do I have to do to get the idle to where it should be in the 600 rpm range? Also, I cannot unscrew the curb idle screw out anymore as I have it out as far as I can get it. I also see that the there are some uncovered vacuum ports like the one on top of my air filter duct, and what looks like two ports near the manifold that are small and black and not capped or connected to anything. Looking forward to hearing any advice you can offer. I am also not worried about any emissions requirement because this vehicle does not need to get inspected in New Jersey.
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Friday, May 5th, 2017 AT 5:29 AM

114 Replies

Tiny
HMAC300
  • EXPERT
First check for a vacuum leak and whether there is a solenoid that hits the carburetor that is for adjusting idle. To adjust carburetor lightly seat air screws then using a vacuum gauge back out for highest vacuum with gauge connected to a intake port or direct port on carburetor that is done after idle is down.I think what you are talking about going to air cleaner is the valve for hot/cold warm up. Also check to see if choke linkage on opposite side of carburetor is applied as that will not allow a regular idle as well see pictures. Also, check that the solenoid is actually working as it may not be and holding throttle open. Then see pictures I think the second picture with arrow may be where your problem is so that lever should be loose if not loosen screw so it does or spray choke cleaner so it will work well.
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Friday, May 5th, 2017 AT 6:38 AM
Tiny
CJA31186
  • MEMBER
So another thing I should mention is that the carburetor is brand new from guaranteedcarburetors. Com. I bought it from them and they deliver it tuned and ready to bolt and go. The choke works perfectly, as it starts really high then warms up and goes down, but not to the 600 rpm range. Solenoid is old, as it did not come with the carburetor, but it does not appear to be holding the carburetor open. I will re-check that, but I am almost positive that is not the problem. Most likely a vacuum leak, or something with the vacuum system?
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Friday, May 5th, 2017 AT 7:57 AM
Tiny
HMAC300
  • EXPERT
Well a vacuum leak can do that as well what was previously mentioned. I am sending a picture of solenoid where arrow points if solenoid works this should be fro idle adjustment and other screw on carburetor should be for around 550 rpm. So when key is turned off solenoid stops and lets engine kind of choke itself out. See picture. If yours is not working then that is still the adjustment as it should allow throttle to come done unless the solenoid is frozen in place. If that is the case take it off and throw it away and use regular idle screw.
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Friday, May 5th, 2017 AT 9:28 AM
Tiny
CJA31186
  • MEMBER
Ok, so it seems that the solenoid, wasn't doing much, so I took it off and capped the vacuum port. I have adjusted the air mixture screws so that now the vehicle idles smoothly. I started unscrewing the curb idle screw to bring the idle rpm down, but when I unscrew the curb idle screw, it just creates a space between the end of the screw and the piece of metal the curb idle screw is supposed to hit. So essentially, I can back out the curb idle screw more but it doesn't change anything because lever doesn't move forward at all. There is nothing blocking it from moving. I tried to push it forward, but it wont go. Is that supposed to be like that? Do I need to go back and adjust the mixture screws again to bring the idle down even though it's idleing smoothly?
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Saturday, May 6th, 2017 AT 11:44 AM
Tiny
CJA31186
  • MEMBER
I don't know if the lever has the capability to move forward because it doesn't go even when pushing it. Moves fine the other way to accelerate the engine, just doesn't go any further closed than where it is.
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Saturday, May 6th, 2017 AT 11:46 AM
Tiny
CJ MEDEVAC
  • EXPERT
OK I finally made it here.

I reckon there's no need to paste in the message/ questions you sent me. Sorry I took so long, doing Honey-D0s most of the morning and early afternoon.

This thing still got the 'lectric choke?

Is the choke's butterfly standing fully vertical?

I was gonna tell you that messing with the idle screws is fruitless when the idle is like 800 RPM and above. You are then running on the mains and not the idle circuit so the screws sorta do nothing for the idle. Like mentioned up above there, many times it's a vacuum leak that throws the whole tuning deal out of whack. And continues to if you ain't capped or fixed all of 'em!

Which carb you got? The BBD with or without the stepper motor on the back?

How 'bout any other modifications?

Any bells and whistles that are not stock?

I already know your vacuum lines have been changed/ removed.

If you are not subject to emissions testing due to the age of your rig or just live in an area like me, it only takes two vacuum lines (PCV and Distributor vacuum advance) are need to run the engine, another one, if you have power brakes.

You are welcome to send pics of your engine from different angles (breather removed) and even some of the whole Jeep!

I've got more tuning for you, let's get the carb operating good 1st.

Try to answer the questions above.

The Medic
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Saturday, May 6th, 2017 AT 12:40 PM
Tiny
CJA31186
  • MEMBER
I have the bbd carb with the stepper motor on the back. I bought it newly rebuilt from guaranteed carburetors. Com. No modifications to the engine that are present. Looks like some of vacuum tubes are not there, but I have capped off all the open ports. 2 caps on 2 ports that are black and stickig out of the manifold area, capped the port to my air filter intake hose, removed the solenoid from the carb as it appears rusted and broken. Also capped a vacuum port on the driver side bottom area of the carb closest to the wheel well and firewall. There were some other ports that were capped that sit on top of the valve cover. Will send pictures shortly. Also have power brakes.
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Saturday, May 6th, 2017 AT 1:05 PM
Tiny
CJA31186
  • MEMBER
See these images. Yes the choke butterfly stands completely vertical when fully warmed. Also have power brakes, aluminum valve cover and electric fan with aluminum radiator. Valve cover does not leak.
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Saturday, May 6th, 2017 AT 1:32 PM
Tiny
CJA31186
  • MEMBER
More pictures
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Saturday, May 6th, 2017 AT 1:33 PM
Tiny
CJA31186
  • MEMBER
More just in case
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Saturday, May 6th, 2017 AT 1:39 PM
Tiny
CJA31186
  • MEMBER
This has an Automatic choke. To set it I step on the gas which closes the choke plate. Not sure if it's electric, just automatic. Once warmed I step on the gas again to get it to a slower idle.
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Saturday, May 6th, 2017 AT 1:42 PM
Tiny
CJ MEDEVAC
  • EXPERT
Idle should be 600 RPMs at 13 BTDC

actually seen as 13 BTDC at 600 RPM

This would be your final close the hood settings.

Did you get the idle screw to touch?

Are your steps still engaged (not floppy loose in front of their adjustment screw) allowing the actual idle screw to touch?

Do you know how to set your mixture screws correctly?

Have you checked your timing?

Do you have a dwell meter/ timing light/ vacuum gauge?

Old pic below of my neighbors neglected '83 carb (and Jeep)

The Medic
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Saturday, May 6th, 2017 AT 3:57 PM
Tiny
HMAC300
  • EXPERT
The idle screw is made to only go so far and idle was controlled by the solenoid like I originally said. It is /was for emissions so either get another solenoid or put the old one back on andsee if you can adjust eh screw in back from the original pics I sent you. Showing which to adjust.
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Saturday, May 6th, 2017 AT 3:58 PM
Tiny
CJ MEDEVAC
  • EXPERT
But the carb must idle back down!

So if you snatched out all of the adjustment screws

(and the non-existent now, solenoid, was still there)

The shaft would still have to rotate the throttle plates to the idle position.

Unless the steps were in the way of it's adjustment.

CJA31186 can you send us a closer-up of your steps?

How low can you get the RPMs at present?

The Medic
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Saturday, May 6th, 2017 AT 4:14 PM
Tiny
CJA31186
  • MEMBER
I have not checked my timing. I have a multimeter that measures dwell. I don't have a timing light or vacuum gauge, but can get them if I need them. I am pretty sure I know how to set the mixture screws correctly, but maybe I am wrong. You can see below what I did to set the mixture screws.

I look at the steps and they are not in the way of the adjustment. When the jeep is warmed up, the screw that was touching the ridged portion of the steps, now touches the top smooth area. I use my multimeter to measure the RPM's, and the best I can get it to run is with the rpms around 780-820 (the multimeter fluctuates a little bit, doesn't stay at exactly one rpm). That's with the low idle adjustment screw all the way out. You still see threads showing on the low idle screw, but if I take it out anymore the throttle will not go any further down, and just create a space in front of the low idle screw. Nothing is holding it back I just think the carburetor cannot go any lower in terms of the idle adjustment. If I turn the mixture screws any more clockwise to get the idle lower around 670-730 range, the engine will run rougher, and will stall out when I stop quickly when driving. So I have the mixture screws backed out about maybe a 1/4 to 1/2 a turn away from the spot where the engine will idle rougher and stall out when stopping. (The solenoid does nothing for the idle with or without it theres no difference.) At this point the only adjustment I can do for the curb idle screw is turn it clockwise to make the idle go higher, but can't go anymore counter clockwise because the piece that the accelerator cable is connected to seems to be at the lowest it can possibly go.

I will also upload a picture of the carburetor screws so you can see what I am talking about.
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Saturday, May 6th, 2017 AT 5:21 PM
Tiny
CJA31186
  • MEMBER
Here is a picture. Also, if there is a way I can get rid of the vacuum lines and emission crap to make the engine run better, I would not mind doing that either.
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Saturday, May 6th, 2017 AT 5:38 PM
Tiny
CJA31186
  • MEMBER
Also, forgot to add, how can I check to see if the timing is at 13 BTDC?
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Saturday, May 6th, 2017 AT 5:48 PM
Tiny
CJ MEDEVAC
  • EXPERT
We'll get to the timing soon!

Let's see if this makes a difference, if indeed, the throttle linkage is holding the carb open.

From the idle speed screw, look at the throttle arm. There's a rod with a ball socket on each end. It connects the arm to the throttle bell crank.

Pop the rod off of the arm, Now the linkage has no bearing on the carb.

Can you get the idle down now?

Forcing it is not the answer (other stuff can be damaged)

Without seeing this situation, sometimes it's hard to explain.

In a correct situation, if there is a gap between the idle screw and it's stop/ anvil (whatever!) This would mean the throttle plates are COMPLETELY shut, it should not run at all.

It's hard to tell if they are completely shut on a mounted carb (things bent or internally binding might affect proper closing).

Turning the screw till it touches would sorta be zero, additional turning would begin to crack open the plates (which is, where it will begin to run)(or turning it a bit too far and backing it down to proper idle speed.

Gimme these answers so I can see if we are starting to get somewhere. Maybe we can get the demons out so you can continue!

I'll then send you a link that should help you get things checked out and get this tuned right.

Oh Yeah! Nice Lookin' Jeep!

The Medic
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Saturday, May 6th, 2017 AT 8:35 PM
Tiny
HMAC300
  • EXPERT
The pic and shows single arrow is for fast idle try adjusting the screw with double arrow outward and see if idle goes down
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Sunday, May 7th, 2017 AT 7:37 AM
Tiny
CJA31186
  • MEMBER
Ok, yes the screw with the double arrow is the screw I am talking about. So, today I tried disconnecting the throttle arm to see if the idle would go further down. It did not go any further down than where it currently is. If you see the picture in the last post with the double arrows, if I turn that screw any more out, the throttle linkage doesn't go any further. I think I have it set as low as it can go. When I take it further out the screw also gets a little wobbly. Should I try adjusting the air mixture screws again to bring the idle down to where it will almost stall then screw in the curb idle screw to bring it up a little? I mean I don't know if that will work either because the jeep seems to run a little rougher when using the air mixture screws to bring the idle down.
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Sunday, May 7th, 2017 AT 11:28 AM

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