Adjusting rebuilt carburetor
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Fleet Mechanic
Joined: Aug 2005
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Adjusting rebuilt carburetor
I need to re-adjust everything on a 2150 carburetor. The one I have is aftermarket. It's pretty much pot metal. I had numerous screw strip out or just not cooperate. It's back together and fine, but not something I'm going to be keeping long term.
Anyway, I need to adjust everything. My haynes manual SUCKS. I can't believe they even sell these. It's half inch thick. No pictures, the text for the entirety of the carburetor adcjustment is 4 bullet points and 1/4 of a page. It sucks. Nothign like my old Chiltons as a kid. What a shame.
Anyway, this has some bi metal choke, vacuum assisted choke. As I said, I need to adjust that and the idle and everything. I can't find a concise source for this information. The black choke cover has NO MARKS AT ALL, so I have no idea how you index it. Does anyone have a link?
I FOUND THIS, IS THIS ALL I NEED TO ADJUST ON THIS CARB?
Anyway, I need to adjust everything. My haynes manual SUCKS. I can't believe they even sell these. It's half inch thick. No pictures, the text for the entirety of the carburetor adcjustment is 4 bullet points and 1/4 of a page. It sucks. Nothign like my old Chiltons as a kid. What a shame.
Anyway, this has some bi metal choke, vacuum assisted choke. As I said, I need to adjust that and the idle and everything. I can't find a concise source for this information. The black choke cover has NO MARKS AT ALL, so I have no idea how you index it. Does anyone have a link?
I FOUND THIS, IS THIS ALL I NEED TO ADJUST ON THIS CARB?
This is going to be a long one. But I want your problem to be fixed. Read up.
Instead of experimenting trial-and-error with the float level, only set it to the factory specification. If you do that and you still have problems, the problem is elsewhere. You can't mask another problem by compensating with the float level.
Since the carburetor is already on the engine, check the wet height of the float. Start the motor and let it run until it's at operating temp, and remove the air horn from the carburetor to expose the fuel bowl. Measure the distance from the center of the fuel level to the top machined surface of the fuel bowl, and this is the wet height. The rebuild sheet will specify what this height should be. If your measured height does not match the specified height, you must remove the float, bend the tang, and start over. Don't forget to snap the float retainer in place when you replace the float.
Be careful when you remove or bump the float, as fuel will spray out of the needle. Also be careful when doing this check, because you have an open fuel source and a running motor. Do this step correctly, and we can take the float out of the picture. Don't waste your time playing guessing games when working with carburetors. Take the time to do things right and do them once, and you won't have problems.
Here is how you take care of the choke and fast idle issues. Once again, proper procedures dominate shade-tree trial-and-error time and time again. Please read my instructions carefully.
Choke pulloff clearance. When you get in any carbureted vehicle to start it first thing in the morning, you push the gas pedal once to "load the choke." This snaps the choke plate shut all the way. Because it's just a spring, its job is to tighten itself. It can't accurately control "how much" it tightens. If we just let the choke pull the choke plate all the way shut when you first start the motor, there will be no way for air to get into the engine. Therefore there is a "choke pulloff" which serves to slightly open the choke plate against the choke spring tension, just enough for air to pass in. The vacuum created by the starter cranking the motor pulls the pulloff diaphragm and lets that first sip of air through.
To adjust the choke pulloff, the motor must be cold and shut off. Loosen the 3 choke cap retaining screws and rotate the choke 90 degrees toward the back of the truck to completely shut the choke. Then, find the choke pulloff vacuum motor on the rear passenger side of the carb. There is an arm coming out of it which actuates the choke linkage. Press the arm all the way in to simulate vacuum pulling the diaphragm, and the choke plate should open slightly. In your rebuild sheet will be a "pulloff clearance" specification and it will be something like 3/32" and such. You must take a drill bit of this size and insert it between the rear of the choke tower and the back-end of the choke plate, to measure how far it is open. It acts like a feeler gauge. There is a small set-screw in the back of the choke pulloff. If your pulloff clearance is not to specification, you must adjust that screw and start the procedure over.
Fast idle index. While the choke is engaged, there is a mechanism to raise the idle above curb idle because the enriched fuel mixture requires the engine to run at a higher RPM. There are two settings for this - fast idle speed, which controls engine RPM during this time, and fast idle index - which controls how much of the choke engagement time that the linkage actually contributes.
When things are functioning properly on a Motorcraft 2V carburetor, there are 3 stages to startup - start, fast idle and curb idle. A small cam on the passenger side of the carburetor has 3 steps and controls this. When you first start the truck and you load the choke in the morning, the engine starts at its highest possible RPM and the throttle linkage is on the first step of the cam. When you bump the gas pedal again, the fast idle linkage is released and allowed to drop, at which point the throttle linkage is on the second step of the cam. The throttle linkage remains on this step of the cam for the entire length of time the choke is opening. Once the choke is completely open, the cam drops out of the linkage completely and the carburetor returns to curb idle. This is where the engine remains for the rest of the driving until the engine cools down again the next morning, and the process starts over.
To properly idle during warmup, it is imperative that you sync your choke with the fast idle cam. Again, there is a factory procedure for this. If you're with me so far, your choke cap is still rotated 90 degrees from when you were setting the choke pulloff clearance. Here is where to go from there:
1. If the choke isn't rotated toward the back of the truck already, do so now.
2. Open the throttle, and hold it there with one hand.
3. With your other hand, push the choke pulloff rod in all the way, the same way you did in the pulloff clearance procedure. The choke should now be open in the pulloff position.
4. Your other hand is still holding on to the throttle. Let go of the throttle, so that it rests again.
5. Now the important part. Look down at the fast idle linkage, underneath the choke cap on the passenger side of the carb. There is a small cam above the throttle shaft. You will see a small V notched onto the second step of the cam, and you will see a long screw with its tip touching the surface of the cam. The tip of this screw must be aligned perfectly with this V. This is the measurement Ford uses to tell you that you've set the fast idle index properly. If it is not aligned with the V, there is a small hex screw on the plastic fast idle arm in the linkage. You turn this to adjust the index. Each time you adjust this screw, you must start this procedure over and check for alignment.
6. Note that anytime you adjust pulloff clearance, you must adjust fast idle index. This is why I had you check the clearance first, before doing this procedure. Make sure one thing is right before you move on to the next.
This configuration gives the following results: when you first start the engine, the idle is high. Once you get out of your driveway and start driving while the engine is still warming up, the idle is still high, but not as high as when you first started it. Once the truck is warmed up completely, the choke is open and the idle returns to normal.
Fast idle speed. Once your fast idle cam is properly aligned, you must adjust the speed at which the engine idles when the fast idle is engaged. You will notice that under fast idle, the throttle plates are open further. I usually adjust this to allow the engine to run at a 200-300 RPM higher than curb idle. Contrary to most of my statements in this post, this adjustment can be trial-and-error provided the linkage is working in the first place.
Choke cap index. If you're still with me, the choke cap is rotated toward the back of the truck. Now you must align it properly. On the rim of the black choke cap is a small notch. On the metal choke housing to which it attaches are seven notches. The goal here is to align the notch on the cap to one of the seven notches on the housing. Going from the back of the truck toward the front, the notches are represented as 3 Rich, 2 Rich, 1 Rich, Index, 1 Lean, 2 Lean, 3 Lean. On the emissions label attached to your hood or valve cover, it will say which notch to align the choke to. If your label is long gone, 1 Rich is usually a safe ball-park figure. This adjustment is often changed during winter and summer season changes. While you're doing this, this is a good time to make sure the choke spring is properly engaging the choke linkage tang inside the housing, as this is often overlooked during a carb rebuild. Once you have the choke cap aligned, tighten the three retaining screws back down.
If you follow the procedures above, your choke and fast idle will be set properly. Like I said before, proper carburetor performance comes from closely following proper procedures, not making guestimates. Ford engineers marked these carbs with all sorts of notches and numbers for a reason - so that they may be tuned properly.
Instead of experimenting trial-and-error with the float level, only set it to the factory specification. If you do that and you still have problems, the problem is elsewhere. You can't mask another problem by compensating with the float level.
Since the carburetor is already on the engine, check the wet height of the float. Start the motor and let it run until it's at operating temp, and remove the air horn from the carburetor to expose the fuel bowl. Measure the distance from the center of the fuel level to the top machined surface of the fuel bowl, and this is the wet height. The rebuild sheet will specify what this height should be. If your measured height does not match the specified height, you must remove the float, bend the tang, and start over. Don't forget to snap the float retainer in place when you replace the float.
Be careful when you remove or bump the float, as fuel will spray out of the needle. Also be careful when doing this check, because you have an open fuel source and a running motor. Do this step correctly, and we can take the float out of the picture. Don't waste your time playing guessing games when working with carburetors. Take the time to do things right and do them once, and you won't have problems.
Here is how you take care of the choke and fast idle issues. Once again, proper procedures dominate shade-tree trial-and-error time and time again. Please read my instructions carefully.
Choke pulloff clearance. When you get in any carbureted vehicle to start it first thing in the morning, you push the gas pedal once to "load the choke." This snaps the choke plate shut all the way. Because it's just a spring, its job is to tighten itself. It can't accurately control "how much" it tightens. If we just let the choke pull the choke plate all the way shut when you first start the motor, there will be no way for air to get into the engine. Therefore there is a "choke pulloff" which serves to slightly open the choke plate against the choke spring tension, just enough for air to pass in. The vacuum created by the starter cranking the motor pulls the pulloff diaphragm and lets that first sip of air through.
To adjust the choke pulloff, the motor must be cold and shut off. Loosen the 3 choke cap retaining screws and rotate the choke 90 degrees toward the back of the truck to completely shut the choke. Then, find the choke pulloff vacuum motor on the rear passenger side of the carb. There is an arm coming out of it which actuates the choke linkage. Press the arm all the way in to simulate vacuum pulling the diaphragm, and the choke plate should open slightly. In your rebuild sheet will be a "pulloff clearance" specification and it will be something like 3/32" and such. You must take a drill bit of this size and insert it between the rear of the choke tower and the back-end of the choke plate, to measure how far it is open. It acts like a feeler gauge. There is a small set-screw in the back of the choke pulloff. If your pulloff clearance is not to specification, you must adjust that screw and start the procedure over.
Fast idle index. While the choke is engaged, there is a mechanism to raise the idle above curb idle because the enriched fuel mixture requires the engine to run at a higher RPM. There are two settings for this - fast idle speed, which controls engine RPM during this time, and fast idle index - which controls how much of the choke engagement time that the linkage actually contributes.
When things are functioning properly on a Motorcraft 2V carburetor, there are 3 stages to startup - start, fast idle and curb idle. A small cam on the passenger side of the carburetor has 3 steps and controls this. When you first start the truck and you load the choke in the morning, the engine starts at its highest possible RPM and the throttle linkage is on the first step of the cam. When you bump the gas pedal again, the fast idle linkage is released and allowed to drop, at which point the throttle linkage is on the second step of the cam. The throttle linkage remains on this step of the cam for the entire length of time the choke is opening. Once the choke is completely open, the cam drops out of the linkage completely and the carburetor returns to curb idle. This is where the engine remains for the rest of the driving until the engine cools down again the next morning, and the process starts over.
To properly idle during warmup, it is imperative that you sync your choke with the fast idle cam. Again, there is a factory procedure for this. If you're with me so far, your choke cap is still rotated 90 degrees from when you were setting the choke pulloff clearance. Here is where to go from there:
1. If the choke isn't rotated toward the back of the truck already, do so now.
2. Open the throttle, and hold it there with one hand.
3. With your other hand, push the choke pulloff rod in all the way, the same way you did in the pulloff clearance procedure. The choke should now be open in the pulloff position.
4. Your other hand is still holding on to the throttle. Let go of the throttle, so that it rests again.
5. Now the important part. Look down at the fast idle linkage, underneath the choke cap on the passenger side of the carb. There is a small cam above the throttle shaft. You will see a small V notched onto the second step of the cam, and you will see a long screw with its tip touching the surface of the cam. The tip of this screw must be aligned perfectly with this V. This is the measurement Ford uses to tell you that you've set the fast idle index properly. If it is not aligned with the V, there is a small hex screw on the plastic fast idle arm in the linkage. You turn this to adjust the index. Each time you adjust this screw, you must start this procedure over and check for alignment.
6. Note that anytime you adjust pulloff clearance, you must adjust fast idle index. This is why I had you check the clearance first, before doing this procedure. Make sure one thing is right before you move on to the next.
This configuration gives the following results: when you first start the engine, the idle is high. Once you get out of your driveway and start driving while the engine is still warming up, the idle is still high, but not as high as when you first started it. Once the truck is warmed up completely, the choke is open and the idle returns to normal.
Fast idle speed. Once your fast idle cam is properly aligned, you must adjust the speed at which the engine idles when the fast idle is engaged. You will notice that under fast idle, the throttle plates are open further. I usually adjust this to allow the engine to run at a 200-300 RPM higher than curb idle. Contrary to most of my statements in this post, this adjustment can be trial-and-error provided the linkage is working in the first place.
Choke cap index. If you're still with me, the choke cap is rotated toward the back of the truck. Now you must align it properly. On the rim of the black choke cap is a small notch. On the metal choke housing to which it attaches are seven notches. The goal here is to align the notch on the cap to one of the seven notches on the housing. Going from the back of the truck toward the front, the notches are represented as 3 Rich, 2 Rich, 1 Rich, Index, 1 Lean, 2 Lean, 3 Lean. On the emissions label attached to your hood or valve cover, it will say which notch to align the choke to. If your label is long gone, 1 Rich is usually a safe ball-park figure. This adjustment is often changed during winter and summer season changes. While you're doing this, this is a good time to make sure the choke spring is properly engaging the choke linkage tang inside the housing, as this is often overlooked during a carb rebuild. Once you have the choke cap aligned, tighten the three retaining screws back down.
If you follow the procedures above, your choke and fast idle will be set properly. Like I said before, proper carburetor performance comes from closely following proper procedures, not making guestimates. Ford engineers marked these carbs with all sorts of notches and numbers for a reason - so that they may be tuned properly.
FTE Legend
Joined: Nov 2015
Posts: 30,915
Likes: 4,123
From: Angier, NC
Start with the motor cold like sitting over night. Air filter removed and vacuum ports plugged.
You will need a vacuum gauge and a tack. A timing light may be good too but at this time not needed.
Hit the throttle the choke should close. How hard did it close? As a start I would not have it close too tight.
If it is tight adjust the housing noting what way it looses (lean) and tight (rich). You can mark the face with arrows L & R so you know.
Now with the choke just lightly closed mark the edge of the cap and housing so you know where you are starting from.
The idle speed may have 1 or 2 screws.
If 2 screws 1 is for fast idle and rest on a cam or stepped cam this raises the idle speed when cold. This should be 1200 to 1500 RPM when the choke is on.
The other screw is the normal idle screw. This should be set to the sticker under hood when up to temp but guessing 600 to 700 RPM.
If only 1 screw it will do the same thing as the 2 but rides on the cam / steps when choke is on but I would set this for hot idle and let fast idle be what it is.
Start the motor and see what the fast idle is and adjust as needed with the screw.
As the choke opens you may need to move the throttle to get the fast idle off.
Up to temp and off fast idle set the normal idle speed as per sticker.
Now with the vacuum gauge hooked up you can adjust the idle mixture screws, bottom front of carb.
Turn each one no more than a 1/4 turn to start with. You need to turn out & in till you get the highest vacuum reading.
Keep each screw turned the same in or out. As you get close you may need to only turn the screws 1/8 turn.
You should also hear and see the motor run smooth or ruff when you are close to the sweet spot.
Now most books say turn the screws in for best idle but you are already there with the highest vacuum reading.
You can turn the screws is just a little from highest reading and be ok.
Readjust the idle speed if needed and you are set.
On the choke you may find it dose not stay on long enough then adjust rich, remember you marked R & L?
You may want to remark the housing leaving the first mark so you know where you started at.
Chokes are hard as you have to start when cold and see how it works when it gets hot then you got to let it cold again.
Keep at it and you will get it.
Dave ----
You will need a vacuum gauge and a tack. A timing light may be good too but at this time not needed.
Hit the throttle the choke should close. How hard did it close? As a start I would not have it close too tight.
If it is tight adjust the housing noting what way it looses (lean) and tight (rich). You can mark the face with arrows L & R so you know.
Now with the choke just lightly closed mark the edge of the cap and housing so you know where you are starting from.
The idle speed may have 1 or 2 screws.
If 2 screws 1 is for fast idle and rest on a cam or stepped cam this raises the idle speed when cold. This should be 1200 to 1500 RPM when the choke is on.
The other screw is the normal idle screw. This should be set to the sticker under hood when up to temp but guessing 600 to 700 RPM.
If only 1 screw it will do the same thing as the 2 but rides on the cam / steps when choke is on but I would set this for hot idle and let fast idle be what it is.
Start the motor and see what the fast idle is and adjust as needed with the screw.
As the choke opens you may need to move the throttle to get the fast idle off.
Up to temp and off fast idle set the normal idle speed as per sticker.
Now with the vacuum gauge hooked up you can adjust the idle mixture screws, bottom front of carb.
Turn each one no more than a 1/4 turn to start with. You need to turn out & in till you get the highest vacuum reading.
Keep each screw turned the same in or out. As you get close you may need to only turn the screws 1/8 turn.
You should also hear and see the motor run smooth or ruff when you are close to the sweet spot.
Now most books say turn the screws in for best idle but you are already there with the highest vacuum reading.
You can turn the screws is just a little from highest reading and be ok.
Readjust the idle speed if needed and you are set.
On the choke you may find it dose not stay on long enough then adjust rich, remember you marked R & L?
You may want to remark the housing leaving the first mark so you know where you started at.
Chokes are hard as you have to start when cold and see how it works when it gets hot then you got to let it cold again.
Keep at it and you will get it.
Dave ----
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