I've reached the point where I'm beating my head against my 65 F100, so i come to you hat in hand asking for assistance.

Spec: 1965 F100 Stock 300 Inline, 1V Autolite 1100, stock Ford points distributor. Nothing after market or upgraded.

The truck has always run rich and over the past few months of daily driving it started throwing black smoke. After doing some research here on the forum I decided to start with the carburetor which hadn't been rebuilt since I've owned the truck.

After a full carb cleaning, rebuild, and adjustment per the 65 Truck Shop Manual the truck will only idle with the choke on at between 1300 and 1800 RPM. It will run with the choke off if I give it additional throttle which when checked is also holding it between 1300 to 1800 RPM. Between 1300 RPM and the engine stalling it sounds like what i think of a Big Block with a heavy cam sounds like or even a diesel (I can upload a video if needed).

I verified the points adjustment and the spark plug wires/distributor cap/rotor were new as of 6 months ago and show no wear or damage.

What else would make the engine to not want to run well below 1300 RPM?

 

How are you setting the idle mixture screw? By how many turns out the manual says, or by what the engine actually wants? Are you adjusting it after it's fully warmed up? Carbs usually don't just go rich by themselves unless the float is leaking and sinking, it could be that the spark is weak enough that not all of the fuel is burned so it seems rich but it's actually an ignition issue.

If it won't run without the choke closed then its probably running too lean; open up the idle mixture screw to add more fuel and see if that helps.

The "lean best idle" mixture screw adjustment shown here is the best way to set the idle mixture screw.

CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT

 

Vacuum leak somewhere. Double check your work.

 

X2
Time to use carb cleaner or brake clean and start spraying it around the carb and intake manifold to find that vacuum leak.
Dave ----

 

Also check that the timing pointer on the timing cover lines up with the “0” on the harmonic balancer when the #1 piston is @ tdc. Harmonic balancers can and do slip which causes wrong timing settings.

 

First thank you to everyone for the input, work got crazy and i am just now getting back to the truck.

Per the shop manual i started with the idle mixture screw at 1 1/2 turns out and then adjusting the idle adjustment screw to obtain the desired RPM. However I can never get the engine to the desired RPM range cause it wont run without the choke on, even after running for 30+ min. Adjusting the idle mixture screw with the choke on make little to no difference.

Started with the idle mixture screw at 1 1/2 turns out per for he shop manual adjustment instruction. The first step in the manual is to adjust the idle adjustment screw to obtain the desired RPM, this

I used an entire can of carb cleaner spraying down every gasket, hose, etc and found no area that in anyway effected the RPM or tone of the engine running.

I will check this today.

 

You need to get a vacuum gauge to help diagnose why it will not idle. Also do a compression test. It may be possible that there is a camshaft issue.

 

You sound like you're having a similar problem to what I struggled with for a long time. I have a 1965 w/240 engine, almost all original - with orginal Autolite 1V carb. I originally had a lot of trouble getting the engine below 900 RPM. I tried rebuilding the carb but that didn't make any big improvements so I sent it off to have it rebuilt. Rebuilt carb was better but I still couldn't get the idle below 750-800 RPM. I also changed to a REMFLEX gasket which also helped but it was still stumbling at low RPM. I ended up getting a Holley 1940, 1V carb (which was a service replacement for the Autolites) to try. It gave me similar results so I started concentrating more on vacuum leaks. I got a new base gasket, changed the metal vacuum line to the distributor to vacuum tubing w/barbed fittings, replaced the SCV, and replaced the throttle spring. All of these things added up to me finally getting my idle down to the service manual range of 550-600 RPM. Based on my experiences, I agree w/Dan - possible 1 (or in my case more than 1) vacuum leak. I would check base gasket, vacuum fittings, SCV, main throttle shaft, throttle spring, and intake manifold for vacuum leaks in addition to the usual suspects. Good luck!

 

I'm gonna chime in with a few ideas:
First is the idle circuit. Throttle plates must only be covering the idle circuit slot by about 1/3 for a base line.

Second: if your idle mixture screw doesn't kill the engine when screwed all the way in, _ _ _ you have too much air, or, you idle circuit is not delivering fuel.

Third: check your vacuum and see if you are running 18-21 inches.

Berryman's carb cleaner in spray can is good for spraying around fittings and intake manifold to chase vacuum leaks.
If a leak, the engine should speed up.

You have changed carbs with little difference, so you must be chasing a vacuum leak.

 

If you used a full can of cleaner spraying everything and did not find anything I think I would pull the carb off and pull it apart rechecking my work.
Maybe a gasket was installed wrong or got cut and the leak is with in the carb.
I had a Holley v4 carb that would also only run good with the choke on and could not find a vacuum leak anywhere.

Even rebuilding the carb did not fix it but I matched all the new gaskets to the old so if a PO used the wrong gaskets so did I.
I ended up replacing the carb and that fixed the vacuum leak. The old carb must have been leaking internally.

The other thing to do is look up checking for vacuum leaks using smoke on YouTube.
If you can put smoke into the intake manifold flooding it it has to come out somewhere and if it is coming out anywhere but the carb you got a leak.
Remember to plug the PCV hose or you it to put smoke in the intake.

That reminds me I got to get the wife to order parts from Amazon to make a smoke machine as I got a buddy that has a issue like yours on a 85 Olds that just started 1 day and a different carb did not fix. I think it is a bad intake to head gasket pulling from the valley and why spraying did not find it.
Dave ----

edit: Just a thought on the later 300 motors (80 - 86) there is a vacuum tree on the lower back side of the intake.
Most of the ports have caps on them. There is 1 way in the back to the motor side that is hard to see. this cap dries out and cracks and causes a vacuum leak. See if you have something like this. Again it is hard to see all the ports.

 

Update: With help from all of you i was able to track down and resolve a number of issues.
*Replaced leaking PCV grommet
*Replace carb jet, a 87F was installed but the Ford Shop manual called for a 55-67. Replaced with a 61.
*Set static timing show that timing was way off.
*Adjusted timing to 6 BTDC
*Checked point and found the plastic surface that engages the distributor shaft had worn down and the point were barely opening. Adjusted to .025.

The engine now idles at 600RPM instead of 1800RPM, and i will keep working on it and adjusting now that things like the air/fuel mixture screw actually do something.

Thank you everyone for your help on this post and the entire forum.

 

Great news! Nice display of patience and problem solving!

 

I might have been premature with my celebration.

After doing all the work above and a few test drives i noticed the engine running hotter then usual. I checked the coolant levels, left radiator open to see everything move to make sure therm wasn't stuck closed. So i let it idle to see if it was getting hot all the time or just under load, sure enough about 30 minutes of idling at 600 RPM on a 62 degree day the engine was at 220 and climbing. I went to check the temp with my infrared laser but just my luck it doesn't want to work so i ordered a new one.

I double checked the points and they are still gap'd correctly, checked the timing and it's still 6 BTDC, then i checked the spark plugs and they had gone from black with the 87 jet to white showing it was running lean. I tried adjusting the fuel/air mixture per the shop manual but when unscrewing it would never get rich enough to cause the RPMs to drop. So i changed the meter jet from a 61 to a 65 and tried adjusting the air/fuel again but got the same result no drop in RPMs. So i again replaced the jet this time with a 68 (shop manual says 57-69 depending on carb model # and my carb doesn't have any numbers on it) and still unscrewing the air/fuel mixture screw it doesn't cause the RPMs to drop and the spark plugs are still showing white like it is running lean.

Any idea what am I 'missing?

 

Sounds like it could be a timing issue
At idle, without advance, the engine will get hot
I think you have a load a matic, which I don't know about. But double check your vac hoses are connected to the distributor correctly, and that your timing is correct.
Static at 6 is fine, but you should see something much higher at idle when the advance system is connected and working properly