Motorcraft 2150 adjustments?

[Clunker]

I've fixed all the vacuum leaks, and I'm ready to take a look at the carburetor. The truck seems to hesitate when I hit the throttle, but I made some observations today that may indicate that I'm running too lean. Tell me what you guys think.

Specs: 1970 F250 camper special, 360, C6, RWD, Pertronix (with new plugs, wires, cap, rotor, coil), rebuild with about 35k and hardened valve seats, professionally rebuilt Motorcraft 2150 carb.

The truck has had some throttle hesitation since I bought it. Here's what I know so far. The ignition timing is set at 10 BTDC. The engine runs pretty smooth but needs a little extra gas to get started. The choke functions but isn't really the right setup, so it takes a while for the choke to disengage. My observation today was that the truck did not hesitate until the engine warmed up enough for the choke to disengage. I was thinking that since the engine didn't hesitate when running with the choke engaged (when it's running rich), maybe I'm running too lean. I figured that I would check the float level first, and then take a look at the mixture screws, but I'm new to the Motorcraft carbs. Do I understand correctly that one screw is for one barrel, and the other is for the other side? Can anyone give me a really basic procedure for how to set the mixture (How many turns from all the way in before starting, etc.)? I have a vacuum gauge if that helps. Thanks all.

[Art]

I've fixed all the vacuum leaks, and I'm ready to take a look at the carburetor. The truck seems to hesitate when I hit the throttle, but I made some observations today that may indicate that I'm running too lean. Tell me what you guys think.

How does it run compared to before you fixed that vacuum leaks? Vacuum leaks allow air to enter the manifold without going through the carburetor, so they effectively lean the mixture. Now that you have fixed those vacuum leaks, the mixture should be richer than it was before.

Specs: 1970 F250 camper special, 360, C6, RWD, Pertronix (with new plugs, wires, cap, rotor, coil), rebuild with about 35k and hardened valve seats, professionally rebuilt Motorcraft 2150 carb.

Thanks for providing that information. Good thing you have hardened seats, otherwise I would recommend running on the rich side to help prevent exhaust valve seat recession.

The truck has had some throttle hesitation since I bought it. Here's what I know so far. The ignition timing is set at 10 BTDC. The engine runs pretty smooth but needs a little extra gas to get started. The choke functions but isn't really the right setup, so it takes a while for the choke to disengage. My observation today was that the truck did not hesitate until the engine warmed up enough for the choke to disengage. I was thinking that since the engine didn't hesitate when running with the choke engaged (when it's running rich), maybe I'm running too lean. I figured that I would check the float level first, and then take a look at the mixture screws, but I'm new to the Motorcraft carbs. Do I understand correctly that one screw is for one barrel, and the other is for the other side?

That is correct. One idle mixture screw per carb venturi (aka "barrel"). Each venturi feeds four cylinders, and you can see which four cylinders by looking at the intake manifold passages.

Can anyone give me a really basic procedure for how to set the mixture (How many turns from all the way in before starting, etc.)? I have a vacuum gauge if that helps. Thanks all.

Your vacuum gauge is the best tool for optimizing idle fuel mixture.

Start (with the engine off) by turning each screw in gently till it bottoms, keeping track of each screws' number of turns. Return them to their previous settings. Now with the engine running at operating temperature, verify that the choke plate is completely open. Adjust each mixture screw in small increments while watching manifold vacuum. You want both screws to be approximately the same number of turns out, and it usually ends up being around 1.5 revolutions out. Adjust for maximum manifold vacuum, because that is where the engine is happiest.. Counterclockwise richens the idle mixture, clockwise leans the idle mixture. If the engine barely responds to idle mixture screw adjustment, or runs fine with the screws nearly or all of the way in, it is getting fuel from somewhere besides the idle circuit of the carb, and the carb most likely needs attention.

For a quick check you can intentionally create a small vacuum leak (don't use the distributor vacuum hose, though), and listen to how the engine responds. A speed increase means you were running too rich. No change or a slight decrease means you were pretty close. A big decrease in speed means it was too lean.

I typically adjust the idle mixture to favor the rich side of perfect, as I believe it buys me a little cushion of safety. It also helps prevent off-idle stumble and also improves cold engine driveability. To me gas is much cheaper than engine repairs. I also prefer a manual choke as there is no doubt about the choke plate position.

Another possible source of throttle stumble is the accelerator pump. Basically, there should be two streams of fuel squirted into the carb venturis immediately as the throttle is opened. Don't check for this while the engine is running, as a backfire in your face certainly is not pleasant Since air enters the engine immediately as soon as the throttle plates are opened but the fuel flow is slower to respond, a squirt of fuel is required to prevent the engine from stumbling or stalling during that transition period. The accelerator pump is located under the square cover on the front of your carb with a linkage rod going to the throttle arm.

[Manny]

Hey there clunker,

The 2150 is a relatively simple carb for sure. You already have the right idea with the one screw for one barrel that is correct for sure. Now before digging in lets look at the base plate to make sure that it is okay. With the engine running take some carb clean and spray around the base shaft if it smooths out or revs up then the base plate has a vacuum leak and it will never adjust out right. If this works out okay shows not to be leaking. Then hook up your vacuum gauge and read it.You could also do this with the carb spray test and watch the reading. You want to be above 15 inches at best 20 inches. What you will do is twist the screws in 1 at the time until the vacuum falls and the engine runs rough. The come back out till you get the highest reading. Repeat for the other screw. If you twist in too far and kill the engine. Back it out 1/2 turn pat the gas restart and tune again... This will set you idle mixture and increase the vacuum up to allow crisper throttle response. If this does not fix your issues then you may need to look into the accelerator pump. The plunger thingy on the front, and adjust it to provide more fuel for takeoff. So try adjusting your mixture first and we will see what you get.

[Manny]

Wow art we both plowed that field at the same time didn't we???

[Art]

Wow art we both plowed that field at the same time didn't we???

Yeah, but I type slowly and poorly, so I had to go back and correct all of the new words I just invented...

[Art]

One more thing, it is usually best to have the carburetor adjusted so that the engine runs right with minimum throttle opening.

Many times I have seen carburetors 'adjusted' with excessive throttle opening to compensate for other things being out of whack - especially fuel mixture, vacuum leaks, and ignition timing.

[Clunker]

Thanks guys. That's great information and exactly what I was looking for. I don't know if the accelerator pump is functioning at 100%, but it definitely squirts some gas into the carburetor when I move the throttle with the engine off. The manifold is giving me about 17 inches Hg at idle, so I have a decent starting point.

How does it run compared to before you fixed that vacuum leaks? Vacuum leaks allow air to enter the manifold without going through the carburetor, so they effectively lean the mixture. Now that you have fixed those vacuum leaks, the mixture should be richer than it was before.

Every time I find a vacuum leak and plug it, the truck seems to run a little bit stronger but still hesitates when you hit the throttle.

What you will do is twist the screws in 1 at the time until the vacuum falls and the engine runs rough. The come back out till you get the highest reading.

Are you suggesting that I only adjust one screw at a time? Won't unbalanced mixtures also cause the engine to run rough?

One more thing, it is usually best to have the carburetor adjusted so that the engine runs right with minimum throttle opening.

How do you check and adjust the throttle opening? Is that controlled by the idle screw?

I'll start the adjustments this weekend and let you guys know what I find. I imagine it will take a few rounds of adjustments to get all of the components operating in harmony. Hopefully, I don't need to rebuild it. I watched a YouTube video about rebuilding the 2150, and it doesn't look very difficult as long as you can keep track of the enormous number of little parts.

[Clunker]

***Update***

I'm hoping you guys can interpret this info. I tested the entire engine and vacuum lines for any vacuum leaks with carb cleaner and detected nothing. The vacuum gauge showed the same 17" Hg and the idle speed stayed the same. Then I created a small vacuum leak, and the engine started running a little rough, but the engine speed and vacuum gauge didn't change. The accelerator pump is definitely squirting two jets of fuel when I move it. Finally, I checked the mixture screws and found that one was set at about 2 turns from bottom, and the other was set at 2.5 turns. I backed out the first one to the same level as the second one (2.5), and the idle smoothed out, the RPMs increased, and the vacuum gauge went up from 17" Hg to about 17.5".

Sounds to me like the carb was running too lean and out of balance, but doesn't 2.5 turns sound like way too far? I thought the general rule was that the mixture screws should be closer to 1.5 turns. If this is the case, then I probably have another vacuum leak that I haven't found yet. What do you guys think?

[Art]

***Update***

I'm hoping you guys can interpret this info. I tested the entire engine and vacuum lines for any vacuum leaks with carb cleaner and detected nothing. The vacuum gauge showed the same 17" Hg and the idle speed stayed the same. Then I created a small vacuum leak, and the engine started running a little rough, but the engine speed and vacuum gauge didn't change. The accelerator pump is definitely squirting two jets of fuel when I move it. Finally, I checked the mixture screws and found that one was set at about 2 turns from bottom, and the other was set at 2.5 turns. I backed out the first one to the same level as the second one (2.5), and the idle smoothed out, the RPMs increased, and the vacuum gauge went up from 17" Hg to about 17.5".

Sounds to me like the carb was running too lean and out of balance, but doesn't 2.5 turns sound like way too far? I thought the general rule was that the mixture screws should be closer to 1.5 turns. If this is the case, then I probably have another vacuum leak that I haven't found yet. What do you guys think?

I wouldn't sweat it if the engine wants 2.5 instead of 1.5 turns - as long as you are sure there are no vacuum leaks. I like to use a stethescope with an open hose to listen for leaks. You want to maximize manifold vacuum when adjusting the idle mixture.

[Art]

How do you check and adjust the throttle opening? Is that controlled by the idle screw?

Yep.

What I was trying to explain is that it is better to have the carburetor adjusted so that the idle mixture is correct instead of maybe having the idle mixture wrong and the idle speed screw cranked in more to compensate...

[Art]

The accelerator pump is definitely squirting two jets of fuel when I move it.

You want the accelerator pump to squirt two streams of fuel the instant the throttle is opened. Any hesitation will show up as an engine stumble when running.

[Clunker]

The accelerator pump barely needs any movement at all before it squirts quite a bit of fuel, so I don't think I need to worry about it. Even though the engine seems to run a bit smoother after the adjustments, it still has considerable hesitation. Another thing I forgot to mention earlier is that when I'm at close to full throttle going up a steep hill, the engine actually has less power than when I back off the throttle a little bit. This once again suggests to me that it is starving for fuel. Another thing I didn't mention was that the PO didn't drive the truck very much and didn't really do anything to maintain it, and it's possible that after sitting for a long time, some of the internal carburetor parts are gummed up. It looks really clean from the top, but I can't even see the jets. It might be worth my time to just rebuild the thing, so there isn't any question. Of course, this begs the question, if I have to deal with a rebuild, should I consider a new 600 CFM 4 bbl instead of rebuilding the 2 bbl?

[Heirloom]

Three questions for you...

First, on the drivers side of the carb there is a circular raised casting with numbers. 1.08, 1.14 or 1.23 for example. What are those numbers?
Second, what number jets do you have in there?
Third, the accel pump rod connects to a bell crank on the throttle linkage. That bell crank should have 3 or 4 positions on it. Do you have 3 or 4 holes and from the bottom up, which position is yours in?

The 2150 is a decent carb when adjusted right. My 360 runs great with it's 2150

EDIT: And possibly a big part of your tip in stumble, the accel pump should activate the moment you touch the throttle. Very little movement in the throttle blades with out that shot instantly equals a tip in stumble.

[Heirloom]

Just saw your other thread....on ID'ing. Your accel rod looks like someone used it to jimmy a window open! I am curious where your distributor is getting vacuum since the 'spark port' on the carb is capped. Looks like there are a few things here that might get you smoothed out.

[Clunker]

Your accel rod looks like someone used it to jimmy a window open!

Yep! There are a lot of modifications that the PO made on this truck, many of them with questionable skill or judgment. Since this is my first Ford, I have no idea what is stock and what is a modification unless it's something obvious. Does the accel rod look stock to you but damaged, or is it just another jimmy-rigged part?

I am curious where your distributor is getting vacuum since the 'spark port' on the carb is capped.

For a while, I was thinking that something was wrong with the port on my carb because I wasn't getting any vacuum at idle. At that time I had it hooked up to the manifold. Fortunately, another forum member clued me in that the carb port doesn't have any vacuum until you hit the throttle, so the vacuum advance is now connected correctly to the carb port and the manifold port is capped. I tinkered around with the vacuum advance a bit and I'm beginning to suspect again that it is not functioning properly. I read somewhere that you should be able to advance the distributor plate by hand, and plug the port with your finger. When you release the plate while keeping your finger on the port, it should not return to its original position unless there is a leak. I don't know if this is an accurate test, but it failed miserably. If I had a MightyVac, I would just test it properly.

Carb casting number: 1.23
Jets: I have no idea. One of the PO's put in a remanufactured carb somewhere around 2001, but I have no documentation of what size jets were installed.
Pump Rod: The accelerator pump rod is connected to the top hole of 4 holes on the bell crank.