im working on my 85 ford ranger with the 2.8l v6 and 2150A carb with manual transmission.

when im driving it seems like its not getting enough gas. and it jerks like its about to run out unless I have the pedal glued to the floor. so I got the fuel mixture screw out 2 and 3/4 turns. and the idle srew out to where it idles at 900. but it just don't seem like it drives like it did when I bought it. I did notice that the butterfly valve at the top of the carb doesn't open all the way. and im not sure if this is a problem and if it is how to fix it. any ideas on it would be greatly appriceated

 

The Choke plate is at the top of the carb, is that the "butterfly" you are referring to, if so it must be open all the way after engine warms up, or engine will be running too rich.
If you checked it with engine cold then it should be partially closed.
The choke plate is adjusted by rotating the large plastic cap(usually black) clockwise or counter-clockwise.

Has the fuel filter been changed?
There should be one in the frame rail under the drivers seat.

Check the Vacuum line from distributor to carb, make sure it is not cracked or leaking.
This hose advances the spark timing to get more power when accelerating.


Carbs are pretty simple but things can go wrong which is why they need to be rebuilt.

The fuel pump push gas to the carb through the fuel filter
The carb has a needle valve and float, like on a toilet tank, as the gas flows into the "float bowl" the float rises up and closes the needle valve.
For this to work the float bowl must be vented at the top, make sure vents are clear.

A carb mixes gas with air using the velocity of the air and negative pressure(vacuum) the engine's pistons and valves create when engine is turning.
The engine is an air pump, it sucks air in by piston going down with intake valve open and then pushes air out when piston goes up with exhaust valve open.

The carb will have "jets" that stick out in each "barrel" of the carb, air flowing past these "jets" suck fuel out of the float bowl, and that fuel mixes with the air.
(The actual jets are located elsewhere but for easier explanation, the "jets" are what gets fuel into the air stream)
As you open the throttle plate more air rushes past the "jets", so more fuel is sucked out.
If the level in the float bowl is too low then not enough fuel is available to be sucked out at higher RPMs.

Carbs also have an "accelerator pump", probably not your issue, this is filled along with float bowl.
When you press down on the gas pedal the accelerator pump pushes a little extra gas into each barrel of the carb, this prevents a lag time between throttle opening and "jets" adding more fuel.
Slow throttle response would be an accelerator pump issue, accelerator pump doesn't do anything when cruising or slowing down.


This page has pictures and labels for your carb:
http://grantorinosport.org/BubbaF250/carb/carb02.html

 

first off, thank you for that information.

yes the choke plate is what I was talking about. so my question to that is if its not getting enough air to burn the fuel, would it sputter when down in low rpms?

so on the back of the carb i was able to spot a vacuum port that I would say was in use before and now has nothing connected to it. and I know for sure I didn't hook any up to the distributor this last time I put it back in which case I never noticed having to take a vacuum line off. so where at on the distributor would that go.

and as for that port, it is the lowest one on the carb and directly in the middle. so since I wasn't sure as to what it went to I capped it off. this in return made my rpms go down significantly.

 

If engine was warm and choke plate was closed then it could be running rough at any RPM because too much fuel is being sucked in.
The engine sucks in XXXX air and X fuel at 700rpm idle, if you restrict the air then it sucks in XXX air and XX fuel, ratio is actually 14:1, so 14 X to 1 X but I didn't fell like typing that many X's, lol.


On any gas engine vacuum ports between intake valves and throttle plate are "regular" vacuum ports.
Vacuum ports between throttle plate and air cleaner are "ported" vacuum ports.

Regular vacuum is high when RPMs are low(throttle plate closed), and low when RPMs are high, often used for power brakes and PCV valve
Ported vacuum is low when RPMs are low and high when RPMs are high, used for distributor vacuum advance.

Low on the carb(below throttle plate) would be a regular vacuum port, so would suck alot of air in at idle, which would cause a high idle, so capping it was a good idea, unless if was for a PCV Valve, in that case you need to hook PCV valve back up.

On a carb a ported vacuum leak wouldn't be as big a deal since air volume is unmetered, any air coming in above the throttle plate would also pull in more fuel.
On fuel injected engine ported vacuum leak will cause issues.

My mistake, 1985 2.8l would probably have the TFI ignition system, so it would use an electronic module to control spark advance, not a vacuum advance.

Autozone has a nice repair section for just about everything Ranger(and other makes)
Google: autozone ford ranger distributor TFI test

I doubt that's your problem, but just as a "heads up", the TFI ignition system has a 100% failure rate, they are just old now, but they were not a reliable system even when new.

 

so I think I have narrowed it down based on what you've explained and what ive researched is that the choke valve isn't opening up enough. so once I adjust that it should get me closer to my goal.

so again, I appreciate all the helpful knowledge you've provided.