Agreed.

Like I said not once but TWICE, this procedure is for a stock carburetor on a stock or relatively stock engine. And that is what Jghake appears to have.

If he doesn't end up being close to the bench setting of 1-1/2 turns out, something else is amiss. And that could be anything you just mentioned. Adjusting the carburetor too far away from the bench settings to compensate just makes the problem worse. (That is probably one reason why the later smog carburetors came with plugs over the mixture screws: to limit the adjustment.)


Nowhere did Jghake mention he had a vacuum gauge, Chief.


Control issues... re-read the post yourself and stop splitting hairs.

If you set it the way I described it earlier in this post (Ford specifications), you would *only* need to turn the screws one way - and that is "IN." I thought I made that clear in my post. The final "1/4 turn out" I was referring to is not totally necessary but gives a little richer mixture to stay on the safer side, and so he wouldn't have to do a yearly tune-up.

 

There is no such thing as stock today as we are now using fuels with a lower calorific value count than they had in the 1980's , that is automatically going to mean a richer mix to achieve the same results let alone if the cam or llifters are worn, are the rings are sealing as good as new or if the float level is spot on. Again the difference between quoting something from a book and having actual real world functional knowledge. And given all these trucks are are now 30 plus years old it is pretty much a given almost all of them do not have their original carbs and will have parts and emulsion tubes/venturi assembles swapped from who knows what in a rebuilt carb install, plus, is he running a stock motorcraft FA97R air filter or aftermarket cause that is going to affect it.
The 1.5 is the base and adjust from there rich or lean. To assume that it is automatically going to be leaner from there cause the book says so is just stupid.


Again see above.
Quoting form the book is fine providing everything is as it was when it left the factory, and today with these trucks that is more the exception than the rule let alone the change in fuels. As before the shop manual is a guideline don't always take every detail as gospel. That's the difference between quoting from the book and haveing actual functional knowledge on how these system work and what they do.

 

That's the basic idea though. The bench setting IS pig rich, ensuring the engine will at least start. It's not going to get any leaner by turning them further CCW, ever. You can see this with an exhaust analyzer. They are a precision cut or "trimmer" adjustment. Even a 1/8 or less turn moves the AFR a whole point! That's why Detroit made them non-adjustable or nearly so, towards the end of the carb era. Too many guys out there with the "Golden Screwdriver" I guess.

Turn them in (clockwise) 1/4 turn at a time, equally. Engine warmed up, ideally air cleaner on. Give a little time for the fuel to work it's way through and "blip" throttle between each adjustment. Keep both sides adjusted the same. Don't take all day at it though, it loses the crisp adjustment characteristic if engine sits and idles too long.

Keep leaning it out (clockwise) till it just starts to stumble. Juuust shy of that point will be the highest idle/highest vacuum. That's where you want to be. For emissions testing strategies the "lean drop" method was to raise the idle RPM screw slightly against a 25 RPM drop from each mixture screw.

The idea generally is to lean it out as far as practicable consistent with a smooth idle, but the correct setting also has a definite effect on the off idle acceleration, so it's important to get it right. The folks who seem to have to have them turned out 9 turns have something else completely horked. Timing? Float level? I dunno. Somethin'.

 

So I followed the procedure laid out and the idle still surges 200-300 RPM. If I set idle at 600-750 it will usually die. I sprayed carb cleaner on the vacuum lines and there were a few they were leaking so I replaced them and it got a little better but it's still not where I can drive it as it dies in traffic.

What else can cause erratic idle?

 

Float level can really play havoc with where the idle screws end up as it changes the level of the fuel on the emulsion tubes. The large re-builders tend to not always match venturi assembles to a specific carb body so things can get really wonky. More than once I have seen reman carbs with totally mis-matched carb bodies and venturi assemblies that had no hope of ever working properly.
And now with the lower calorific fuel you tend to need to richen stuff up a bit.
The refiners keep adding crap to the fuel in name of making cleaner burning and then displace the amount of high calorie hydrocarbons in it to do so. It is one of those X amount of this from a gallon of gasoline reduce the gasoline content you reduce X.
For EFI vehicles this is not a big deal as they automatically compensate for it. Our old non feedback carb'd vehicles not so much.
Now we need to take the base factory setting with a grain of salt and adjust accordingly to compensate for the fuel in you happen to have in your area. Years back fuel was pretty consistent across the US and Canada. Now the stuff varies wildly across the US. Canada is not quite as bad but there is a difference from west to east.

 

 

 

Did you check your hose going to the distributor? Do you have vacuum on it at idle?

 

Watched your video and listened, and agree with the previous posters. Go back through and re-read them and checkoff the routines they suggest. It sounds a little like the ignition timing is off, and idle too high. It's tough to tell sometimes, because an idling engine has no load on it so will happily idle just about anywhere timing wise.

One classic problem, that I don't know that has been mentioned, the vibration absorber or crank damper, the rubber sandwich holding the steel inertia weight ring degrades and rots from heat and ozone, oil and grease, ring slips and now the timing marks are WAY off.

So someone tries to set timing with a light, and it won't even be close. Need to check for this. Sometimes too people will install the distributor off clock or index as well, and instead of R&R the distributor, they move the wires around. This also makes checking the TDC a mite bewildering at first. One thing that you will get very proficient at if you spend a while working with these old cars and trucks is simply def-uckulating whatever the previous owners screwed up.

So the easiest thing to, what saves time in the long run, is to check everything. Don't "assume" that anything is right. Start from scratch. For this you will need the manuals and specs. These are available for download if you dig around, When I say check everything, that means check everything. Like say, the correct order of the spark plug wires. An engine will idle reasonably well with 2 wires switched, depending. Some people might not even notice.

The thing to keep in mind about carburetors is the old saying "90 per cent of carb problems are ignition related." There's a lot of truth to that. You'll observe that the better the engine is setup the more noticeably crisp and precise the carburetor responds to tuning. For just one example, the amount of ignition timing +/- changes the overall level of manifold vacuum. This is key.

If the ignition timing was/is way off for some reason (not uncommon) a swing of 10° is going to change ALL of the operating points of the carb. It may run terrible, poor economy, overheating etc. Anyway at idle there is actually very little air moving through a carburetor, so a separate, special circuit is required that utilizes engine manifold vacuum.

This is what allows an engine to be throttled way down, slow... and still idle smoothly. That's the mark of a well tuned engine with good hot ignition in good mechanical condition - it will throttle down slooooww and smoooooth. The fuel is being precisely metered and atomized (sprayed) into the manifold. You can hear this when carburetor mixture screws first get dialed in close, it starts to hiss at you.

 

 

 

Thing is you have to check, can't tell by looking really, as far as I know. Bring #1 piston to exact TDC on compression stroke. This should coincide with the timing pointer at "0" on the damper.

Your video: Try setting the idle a little lower. Remember the carburetor "timed" spark port will start to pull vacuum in above a certain point. Make sure the vacuum can diaphragm isn't shot as well, it will introduce a huge vacuum leak. This is common as well.

Now the better question might be what does your vacuum gauge show when connected to a source of manifold vacuum. It should be steady, 18" to 20" at normal factory RPM of 500 to 600 say. Higher elevations less.

 

 

 

We know now that your throttle blades are open too far. When you are setting the timing, you are disconnecting plugging this line to the dist correct? If you are not, you need to do that and then reset the timing.
Speaking of the timing, I am leaning more and more to the other poster's opinion, that maybe your balancer has slipped. My next move if I were you would be to loosen the dist bolt just enough to where you can force the dist to move, but it stays put when you take your hand off it.

Start the engine with the dist bolt just snug, and then turn the dist till the engine speeds up(leave the dist vacuum line disconnected and plugged off. When the engine speeds up, turn the idle stop screw back on the carb to slow it back down. Then check the plugged vacuum line going to the carb. Does it still suck on your finger? If so, turn the dist a little more till the engine speeds up just a little more, turn the carb idle screw back till it slows down again, and then check the vacuum line again.

Hopefully you can get it to where there is no vacuum on the dist vacuum line. If you get to that point, you can get your timing light out and see where you are at. And if you get to this point, your mixture screws are going to be working, so you can fiddle with them and get it idling good. You can then hook the dist vacuum line back up and take it for a test ride.

During your test ride, listen carefully for any spark knock or rattling from the engine.

If this whole procedure sends you do the wrong road, you can easily use your timing light and put it back were it was.