clogged idle air bleed (update)!!!!

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what will a clogged idle air bleed do?

A. make the idle circuit rich
B. stop the fuel to the idle circuit

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What are your idle mixture screws doing?

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put your finger on the end of a straw that has water in it. what happens

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put your finger on the end of a straw that has water in it. what happens

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Im no carb expert, But what little I do know about them is that the air bleeds are there to add air into the fuel mixture for better A/F atomization.

Your right the bowl is vented and that will allow the fuel to flow with clogged air bleeds.

The finger over the straw analogy doesnt relate, because our straw has three holes in it.

Dont worry, If Im wrong, the right answer will come shortly. Its always funner to point out that someones wrong then to give a correct answer in the first place mike

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sounds like a 3 sided question

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Im no carb expert, But what little I do know about them is that the air bleeds are there to add air into the fuel mixture for better A/F atomization.

Your right the bowl is vented and that will allow the fuel to flow with clogged air bleeds.

The finger over the straw analogy doesnt relate, because our straw has three holes in it.

Dont worry, If Im wrong, the right answer will come shortly. Its always funner to point out that someones wrong then to give a correct answer in the first place mike

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niether do

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just for you

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could also be lots of fuel...

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idle fuel exits under the throttle blades

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I know but if it got rich enough to shut the motor off you would think you would see some black smoke. the other 2 circuits are not pulling any fuel with the blades closed so I guess it really doesn't matter if they are blocked at idle. I still think it shuts the fuel flow off when blocked.

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could also be lots of fuel...

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now it sounds like you grasping at straws

try putting your finger on the end of one of them

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Was the video posted to show that when you cover the idle air bleeds the motor dies?

If so what did that proove? Did the motor die because it was lean, or because it was rich?

If you really want to know, cover the idle air bleeds. When it starts to die, tap on the accelerator pump (squirting a little fuel). If the extra fuel saves it from stalling, that means it's lean. If the extra fuel from tapping on the accel. pump doesn't do anything, it's alredy rich.

This is how I fine tune idle air mixture adjustment too. RPM goes up with a tap, turn the screw out. RPM goes down with a tap, turn the screw in.

The idle air bleed is there to "lean out" the idle main well on the way to the idle mixture screw. By having a "leak" in the "straw" (idle main well) it's pulling on, it mixes air in with the fuel going to the idle air mixture screw adjustment. The reason that it needs this is because the quantiy of fuel needed to idle is very small. It would be very difficult if not impossible to regulate 100% fuel with the screw adjustment. By adding in a significant quantity of air, the mixture screw adjustment is a lot more forgiving.

To clarify... I'm using arbitrary numbers here just for example sake. Lets say the motor takes 1 gallon of fuel per hour to idle. (or 1gph)

Lets say 1 turn of the idle screw will flow 10gph
of fuel.

With 100% fuel (no idle air bleed) being delivered to the idle screw adjustment, you can see right away, that if 1 turn of screw can turn 10 times more fuel then is needed, then you'd be trying to adjust the screw by 1/10th of a turn to get it right! Much to fine of an adjustment...

Now take the case where you have an idle air bleed. Lets say the idle air bleed hole is big enough that most of the work being done by the vacuum is sucking air, and very little fuel. (lets say 90% air, 10% fuel).

Now you can see I still need 1gph of fuel to make it idle. One turn of screw can still flow 10gph of mixture. However now since the mixture being delivered to the back of the idle adjustment screw is so lean (remember only 10% fuel now), it takes much more of a screw turn to get that quantity of fuel in the engine. In this case, since you can flow 10gph with one full screw turn x 10% mixture, you end up with 1gph fuel in the engine. By doing it this way, the mixture screw can be much more finely adjusted.

Hope that makes sense!

LOL... by the way, the motor is rich. Try turning the idle mixture screws almost 100% in, and I bet it idles better...

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the off idle ports in the pic, is the refering to the intermediate circuit?

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2 problems I see with that little video test
1 you used the idle circuit and Tony had the High air bleeds blocked 2 different circuits apples to oranges
2 no proof weather it died from to little or to much fuel.

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everytime I feel confident we get another side guess we need a new movie with the pump shot test

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cure= clean the carb make sure everything is clear and go make a pass

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I still want to know

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Ray go make another test movie and tap the pump shot. have sombody look at the exhaust for smoke. and clean your garage while your at it.

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Ray go make another test movie and tap the pump shot. have sombody look at the exhaust for smoke. and clean your garage while your at it.

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i could go buy a new o2 sensor also and prove that fuel stops.

IMO, ToddP is the most knowledgeable carb guy we have on this site. go reread his posts. i just happen to agree with him

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Was the video posted to show that when you cover the idle air bleeds the motor dies?

If so what did that proove? Did the motor die because it was lean, or because it was rich?

If you really want to know, cover the idle air bleeds. When it starts to die, tap on the accelerator pump (squirting a little fuel). If the extra fuel saves it from stalling, that means it's lean. If the extra fuel from tapping on the accel. pump doesn't do anything, it's alredy rich.

This is how I fine tune idle air mixture adjustment too. RPM goes up with a tap, turn the screw out. RPM goes down with a tap, turn the screw in.

The idle air bleed is there to "lean out" the idle main well on the way to the idle mixture screw. By having a "leak" in the "straw" (idle main well) it's pulling on, it mixes air in with the fuel going to the idle air mixture screw adjustment. The reason that it needs this is because the quantiy of fuel needed to idle is very small. It would be very difficult if not impossible to regulate 100% fuel with the screw adjustment. By adding in a significant quantity of air, the mixture screw adjustment is a lot more forgiving.

To clarify... I'm using arbitrary numbers here just for example sake. Lets say the motor takes 1 gallon of fuel per hour to idle. (or 1gph)

Lets say 1 turn of the idle screw will flow 10gph
of fuel.

With 100% fuel (no idle air bleed) being delivered to the idle screw adjustment, you can see right away, that if 1 turn of screw can turn 10 times more fuel then is needed, then you'd be trying to adjust the screw by 1/10th of a turn to get it right! Much to fine of an adjustment...

Now take the case where you have an idle air bleed. Lets say the idle air bleed hole is big enough that most of the work being done by the vacuum is sucking air, and very little fuel. (lets say 90% air, 10% fuel).

Now you can see I still need 1gph of fuel to make it idle. One turn of screw can still flow 10gph of mixture. However now since the mixture being delivered to the back of the idle adjustment screw is so lean (remember only 10% fuel now), it takes much more of a screw turn to get that quantity of fuel in the engine. In this case, since you can flow 10gph with one full screw turn x 10% mixture, you end up with 1gph fuel in the engine. By doing it this way, the mixture screw can be much more finely adjusted.

Hope that makes sense!

LOL... by the way, the motor is rich. Try turning the idle mixture screws almost 100% in, and I bet it idles better...

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my new best friend

We appreciate the real world testing six but it's a good thing holley doesn't engineer carbs this way "hmm you plugged up that port there so that means less fuel... so make dat bigger"

I will admit it's been a while since I've followed the idle fuel and air bleed ports in a holley metering block/main block but if it's anything like the diagrams posted it's clear if you block the idle port you'll have a natural pressure difference from the fuel bowl to the lower idle outlet.

ToddP also makes a good point that the restrictor sizes relative to eachother (air bleed and idle feed) are quite large and that a good amount of air could be supplied by the bleeds themselves. So not only are you supplying more fuel you're blocking off a possible sizeable amount of airflow.

In either case it's too much fuel, and like dizuster says tapping the accel pump is a good way to find out which.

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Chiming in... a stopped up idle bleed will definately make the idle circuit rich. If the bleed is 100% stopped up it probably siphon the entire bowl empty after you shut it off. The same will happen with the main bleed except you will see the discharge port dripping after shut off untill the bowl is empty.
Got to go to a Movie now
Curt

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you were right Curt

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talked to Zach at quickfuel today, he said clogged air bleeds will make the circuit siphon the fuel right out of the bowl and make the circuit rich. so those of you who said that I think you were right.

he also said that it was common for combo's like mine (small cube large carb, intake and heads) to need very large squirters to over come a hesitation at the hit. he said the air speed would be so slow at tip in that it couldn't get enough fuel. last time out I din't have any smaller intermediate bleeds than 57s. since then I have drilled out some 45s which I have in it now and some 40s just in case that isn't enough. with the air bleeds unclogged and the new itermediate bleeds it sounds a lot better and I couldn't detect any hesitation. we will be going back out saturday to give it another shot.

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some good info on this thread, mods should clean the tread up, and tech it in the archives.

I always wonder how this pump shot etc effects a car that leaves off the two step, and trans brake equipped cars were the throttle is floored.
Compared to when at or near idle having the extra accel pump shot all at once.
You would think in this case like Tony's car would NOT see much if any E/T diff foot braking or leaving off a trans brake..While I know I have had cars that picked up in short times off the brake.