Air Bleed Lesson by John Kyle
- Thread starter Newbomb Turk
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Yup. He describes how it works just as you do. Imagine that?
That don't take much.
True Dat!
I watched that earlier today and noted that he did say that timing was affected by the high speed air bleed. He didn't go into detail about timing and I didn't hear him say specificly that a larger bleed delays the start of the main circuit. Although that might be what he would say if asked that specifically I don't know. Perhaps change in timing could refer to the rpm point at which the mixture begins to lean or go rich at the top of the rpm range when the high speed air bleed is changed.
It would be cool if someone would repeat the testing that I did to see if they have the same results. More sources with data that either confirms or has other conclusions would be good for everyone.
Anyone with a dyno out there? Or if you don't have a dyno, the no load part of the test can be done by anyone with a carb that has changeable high speed airbleeds. Simply look down the carb as you slowly raise the rpm and watch the boosters for the point when fuel begins to flow from them. Record the rpm . Change the high speed air bleed and repeat.
Why take someone else's word for it when you can test it yourself?
It would be cool if someone would repeat the testing that I did to see if they have the same results. More sources with data that either confirms or has other conclusions would be good for everyone.
Anyone with a dyno out there? Or if you don't have a dyno, the no load part of the test can be done by anyone with a carb that has changeable high speed airbleeds. Simply look down the carb as you slowly raise the rpm and watch the boosters for the point when fuel begins to flow from them. Record the rpm . Change the high speed air bleed and repeat.
Why take someone else's word for it when you can test it yourself?
Plain as day, wasn't it? That is interesting.
Interesting. He said "if you had a .022" in it and you mash the pedal it would start feeding faster than if you had a .032" bleed in it".
If we take "faster" to mean sooner are we talking micro seconds if there is a difference at all.
Try this at home. Look down a your carburetor and when you say go have someone mash the gas pedal. As soon as you see the throttle move click start on a stop watch. When you see booster start up hit the stop button on your stop watch. Now change the high speed air bleed and repeat the test. If you really did this you would find that the booster start up flow is nearly instantaneous. Don't take my word for it try it for yourself.
If you take "faster" to mean that the fuel is flowing faster through the booster as in more fuel with a smaller bleed then that's a different discussion and up for debate around here.
If there is a change in booster startup by the change in main air bleed size when you "mash the pedal" it would be seem to be micro seconds. I don't think it would be a dominant change. The change in air fuel ratio throughout the fuel curve after booster startup would be the dominant change the engine sees from an air bleed size change.
Another way to think of it is this. If you are foot braking on the line or on a trans brake is the carburetor already at booster startup before you even "mash the pedal"?
I think airflow is the dominant controller of booster start up not high speed air bleed.
Is anyone else willing to test this?
If we take "faster" to mean sooner are we talking micro seconds if there is a difference at all.
Try this at home. Look down a your carburetor and when you say go have someone mash the gas pedal. As soon as you see the throttle move click start on a stop watch. When you see booster start up hit the stop button on your stop watch. Now change the high speed air bleed and repeat the test. If you really did this you would find that the booster start up flow is nearly instantaneous. Don't take my word for it try it for yourself.
If you take "faster" to mean that the fuel is flowing faster through the booster as in more fuel with a smaller bleed then that's a different discussion and up for debate around here.
If there is a change in booster startup by the change in main air bleed size when you "mash the pedal" it would be seem to be micro seconds. I don't think it would be a dominant change. The change in air fuel ratio throughout the fuel curve after booster startup would be the dominant change the engine sees from an air bleed size change.
Another way to think of it is this. If you are foot braking on the line or on a trans brake is the carburetor already at booster startup before you even "mash the pedal"?
I think airflow is the dominant controller of booster start up not high speed air bleed.
Is anyone else willing to test this?
I should add. Of course I would like to be right about this. The ego loves it. But if there is evidence to the contrary that explains why the test I did led me to the wrong conclusion then I would rather be wrong and have a better understanding in the end.
I did the test as a result of listening to other people debate the subject. I was not expecting the results that I got. When this man in the video, who I respect and think is very knowledgeable about carburetors says that a smaller high speed air bleed will start the booster sooner than a larger bleed it seems to make sense and if I would not have done my own test I would have just went with it. But after testing now I'm rethinking and looking at that a little skeptical. In the end I might be wrong or maybe somehow both things are true. It would really help out if someone else would try to repeat the test I did.
I did the test as a result of listening to other people debate the subject. I was not expecting the results that I got. When this man in the video, who I respect and think is very knowledgeable about carburetors says that a smaller high speed air bleed will start the booster sooner than a larger bleed it seems to make sense and if I would not have done my own test I would have just went with it. But after testing now I'm rethinking and looking at that a little skeptical. In the end I might be wrong or maybe somehow both things are true. It would really help out if someone else would try to repeat the test I did.
Great video. Easy for the dumb guy to understand. Thanks for posting.
One more question. Let's say for the sake of argument main air bleed size does change when a booster begins to flow. Who thinks a smaller bleed starts the flow sooner as John seems to suggest ( if I'm not misinterpreting)? And who thinks a larger bleed starts the flow at the booster sooner? And why?
Im going to watch it again. He says it delays the start of the booster IIRC. If not, I should not have posted it because that’s incorrect.
I watched it again and I missed how he said it because he started off with saying “delay” and then went off the rails.
A smaller air bleed will delay the start of the booster. Taylor covered this and the physics haven’t changed.
He got it wrong.
A smaller air bleed will delay the start of the booster. Taylor covered this and the physics haven’t changed.
He got it wrong.
In my mind, the bigger the bleed, the more air is introduced and the more and sooner fuel is introduced. Like a 20 year old gal givin a BJ VS a 35 year old gal. The 35 YO would suck your wiener inside out.
Phone numbers for both please?
It's good info to know if tuning a carb. Big inch, high HP or even a street beater car for best power/economy/etc.
Phone numbers for both please?
It's good info to know if tuning a carb. Big inch, high HP or even a street beater car for best power/economy/etc.
But the 20 year old would suck it in where it counts and 35 year old will probably have an air leak in the worn cylinder.
We have to understand that there is a pressure differential that causes fuel to move up the main well and out to the booster.
I’ll see if I can explain like I understand it.
The booster is X distance above the fuel level in the bowl. And we have a fuel that weighs Y. We need to encourage (or discourage depending on what we want) the fuel to go up the main well and to the booster. I’ll use somewhat easy numbers to make this make sense. The pressure differential between atmospheric, manifold and booster pressure (negative or vacuum) is what makes the fuel start to move. So let’s say the float level (X) is .400 above the first air bleed, and we are using a fuel with the specific gravity (Y) of .750, which means that the fuel weighs 75% of an equal amount of water. And we use inches of water for testing booster draw.
When the engine is off, there is atmospheric pressure (whatever it may be at your locality) on top of the MAB, in the manifold and the booster. And the fuel in the main well is in the emulsion well. All it equilibrium.
Once the engine cracks off there is a signal at the booster. However low it may be, the booster is pulling on the main well. There is still atmospheric pressure on the bleeds and whatever manifold vacuum you have. If at idle manifold vacuum was lower than whatever the booster is seeing fuel
would flow from the booster. We never see that but that is what would happen.
To initiate fuel at the nozzle the manifold vacuum needs to drop far enough so the pressure differential across the booster can pull the fuel that .400 up from the main well to the booster. As I said, there is always a booster signal when the engine is running. Different booster designs on the same engine can have far different pressure drops across them. Which means you’d need a different MAB for each booster type. A straight leg booster won’t provide the same signal as a down leg booster which won’t have as much signal as a good annular booster.
We want to lift the fuel that .400 with a fuel that weighs 75% of an equal amount of water. It takes .4 inches of water pressure drop across the booster to start moving water up the main well. Since we don’t use water but fuel that is 75% the weight of water, we only need .3 inches of water to get the fuel moving.
The MAB has atmospheric pressure on it at all times. The air pushing down on the fuel in the main well comes through the MAB. As you close the size the MAB there is less air pushing down on the fuel in the main well, so it discourages the fuel from heading up the main well until the pressure drop is higher, meaning less manifold vacuum verses atmospheric pressure.
At higher pressure drops across the booster, there is less air pressure on the main well and the fuel curve goes rich(er) because it’s less air introduced into the main well.
A bigger MAB has more air in the main well at lower booster pressure drop, so it encourages fuel to flow to the nozzle at the same pressure drop.
Im not sure that makes sense as I typed it. Taylor in his book says that at low air flow (lower pressure drops across the across the booster) the MAB acts like an emulsion jet. So the smaller the MAB the there is less air to get the fuel moving up the main well.
As you can see, float level affects when the nozzle starts pulling fuel. The booster itself affects when fuel flow starts. The specific gravity of the fuel (weight) affects when fuel starts moving to the nozzle. And the size of the MAB affects when fuel stars to the nozzle. The height of the top emulsion jet relative to float level affects when the fuel starts moving to the booster. And they all affect each other.
I’ll say it like this. The more air in the main well, the lighter the fuel is and less air in the main well and the fuel is heavier.
A smaller air bleed has less air in the main well, so the fuel is heavier at lower pressure drop across the booster and that discourages fuel flow up the main well.
A larger air bleed has more air in the main well, so the fuel is heavier at lower pressure drop across the booster and that discourages fuel flow up the main well.
A smaller MAB delays the start of the booster. A bigger main air bleed hastens the start of the booster.
John Kyle got it wrong.
Not saying I agree with all this but I think you may have mistyped one of these two paragraphs.
No, thats what I meant to say. That in a nutshell is why a smaller MAB discourages fuel flow to the nozzle, and a larger MAB encourages fuel flow to the nozzle.
That’s what emulsion is all about. More emulsion adds more fuel to the main well which makes the fuel light and encourages flow to the nozzle.
The concept is the same with the MAB. More air (bigger MAB) the fuel is lighter and starts flow to the booster with less pressure drop across the booster. Less air (smaller MAB) the fuel is heavier and starts flow to the booster with more pressure drop across the booster.
There is ALWAYS a pressure drop across the booster when the engine is running. It’s easy to see how a good annular booster can use a much smaller MAB because the booster itself will encourage fuel flow from the main well sooner because at the same pressure drop pressure drop across the annular booster verses a down leg. Or a lesser annular booster.
And obviously it will require a smaller main jet with the annular booster because the signal loss across the annular booster is less with the smaller MAB.
Re-read the two paragraphs I quoted. You have a typo in one of them that I'm pretty sure you want to edit.
Ok. I’ll read it in the morning. Im tired and I have to get up early. I thought I proof read it pretty good but obviously I suck at that. And typing.
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