My 4160 idles out of the box at 1600 rpm on the highest step of the fast idle cam. A tap of the pedal right after startup and it drops down to 1000 rpm cold but will rise to about 1300 if I leave it on that step and let it warm up.

 

It has an electric choke. I can check the power source to see if it's 12 or 7 volts, but do you know how I can verify whether the carb requires 12 or 7?

 

See when I cold start mine... I'll pump the peddle two or three times and it fires up and runs at about 1100 RPMs. The choke cover will be closed and slowly open as it warms up, but it does fully open after 5-10 mins just depending on how cold it is. Now it's been running like this I turned in my high idle screw a turn. Before I turned the screw in I would pump the peddle a couple times and when it started it would only run for a few seconds and die.

Now as its idling at 1,100 RPMs it doesn't idle down unless I put it in drive or reverse. It will stay at 1,100 even if I rev it up and even after the choke is fully open.

 

No clunking noise when it goes into gear.

 

The stock Motorcraft 4180 carburetor only used 7V and would have been hooked to the back of the alternator. If you have an aftermarket Holley 4160 carburetor, the choke requires 12V. If the electric choke is hooked to the back of the alternator, it is in the WRONG place, as that location only provides 7V.

First:
Make sure your distributor vacuum advance is connected to PORTED vacuum. Ported vacuum will be plugged into the carburetor and will have *no vacuum* at idle. The correct port will be located on the metering block on the passenger's side of the carburetor on a Holley if I remember correctly. If you have your distributor hooked to full manifold vacuum, that could be why your idle won't come down until you put it in gear. You will also feel your transmission SLAM into gear from Park to Reverse. If the distributor vacuum advance is connected to manifold vacuum, connect it to ported vacuum instead and then re-adjust your curb idle speed (see below).

Second:
Are you adjusting BOTH screws?

The choke fast idle screw is located behind the black choke cap. This screw *only* sets the fast idle when the engine is cold and the choke is ON. Mine is set to 1750 RPM. Turn the screw out for a higher RPM. After the engine has been running for about 20 seconds or so, hit the throttle once to automatically bring down the fast idle cam to a lower engine speed. I think the second step on the fast idle cam will bring the idle down to around 1000 RPM.

The curb idle screw is located on the other side of the carburetor right behind the throttle arm. This screw *only* sets the curb idle speed when the vehicle is fully warmed up and the choke is OFF. Mine is set to 750 RPM in Park. Turn the screw in for a lower RPM. When I put it in gear, idle speed will drop down to 600 RPM.

It sounds like your curb idle screw may be set too high, and that is why it is stuck idling at 1100 RPM when the choke is off. When the engine is fully warmed up and the choke is completely open, turn the curb idle screw *IN* to bring down your idle RPM.

 

Hey condor im no pro or anything but I just went through hassling with my brand new holley on my '86 351, and I have a couple of suggestions for you.
When your truck is running look down the secondarys and see if they are dripping fuel. If they are you need to adjust them. There is a tiny set screw on the bottom side of the carb, you have to take it off, underneath the vacuum diaphram arm. Adjust them to where the fuel veins look like tiny squares.
Is your choke hooked to a constant 12v source or an ignition activated source?

 

That secondary adjustment "usually" doesn't have to be adjusted on a brand new carb. One that is older and has been rebuilt and "fiddled with" may indeed need this adjustment. I have never figured out why they put the adjustment on there so you have to take the carb off to adjust it. And you also have to set it on the edge of a table and crouch down to do it, or hold the carb up high enough to set it, unless you want turn the carb over and dump fuel everywhere.

But most people do not realize, the secondaries do contribute a little bit of air and fuel at all times. They designed it this way in case "grandma" is driving the car or truck, and would never open the secondaries up. If this happened over time, the fuel in the rear bowel would go stale and gum up everything. Setting it up to use a tiny bit all the time keeps the fuel fresh in the rear bowel.

 

I never knew that. Thanks Franklin! When I drive my truck with the Autolite 4100 4V, I make sure to get on it every so often to keep the secondaries from gumming up. I guess now I don't have to do that. I learned something new today!

 

I actually almost took that carb back to o'reillys because I thought it was bad. I didnt even know that adjustment was on there till a couple days ago and now it works perfect.

 

I feel it's good practice to open the secondaries up every once in a while too, like getting on the highway, or that smart-*** in the next lane that "thinks" he can take you off the line. Plus with an open element air cleaner, it just sounds cool!!

 

I believe also you can test the choke unit after maybe a min or 2, it does get quite warm-if yours isn't, it could be bad.

I have an '86 F250, 351W,c6 also and I really noticed that all vacuum lines must be in good shape, disconnect especially the lower big middle one and it dies right out.

Also, is it possible he has a bad accelerator pump diaphram in the carb? And have you checked the front and back float height? Open the small brass screw carefully, don't lose it, or it's little gasket, and then loosen the big nut on top and 'loosen' it until gas just dribbles out at idle (warm I suppose), or 'tighten' it to reduce if it's dribbling out too much.

Also make sure all linkages are clean and working freely. My 2 cents.

 

Did you know a open type air cleaner affects when the secondaries open? They will open later with a open element cleaner, since there is less restriction, so there is less signal to the secondary diaphragm. Nothing that can't be tuned out, but thought you may be interested to know. I do not like open element air cleaners on trucks driven in the winter.

 

My air cleaner isn't hooked up so all the ports are wide open...never did work. Not sure how that'd affect it...other than horrible mpg, my truck runs fine.

 

Its not hooked into the back of the alternator. It has its own plug out of a wiring harness that runs next to the alternator.

From the diagram that I have it is hooked up to the correct vacuum port. In my diagram it shows the vacuum port thats directly above the idle mixture screw on the passenger side of the truck as the, "timed spark vacuum source."

Although...When it does shift into gear it does seem to slam into gear. Its a very hard engagement, but the transmission that I just put in this truck had been sitting for at least a year if not 18 months so I was contributing the slamming as a side effect of the transmission sitting inactive for so long. I have some trans-tune in it and was hoping that it may help its engagement over time...

I had time to play with the carb more tonight and found that the high idle screw had been turned out so far it was almost ready to fall out. I turned it in a good ways and when it fired up she was running around 2,000 RPM's off the bat. As it ran for about 2 mins it idled up to 2,200 then once I tapped the peddle it dropped down to 1,200. I let it run for 10 mins so the choke could open up and once it did i turned the curb idle screw down so it was idling at 1,000. Once I put it in gear is dropped down to around 500-600. I'll have to play with the high idle screw some more, but it seems to be cooperating a little more than it has.

 

I have checked the float height on the front and back and they are both good.