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 Post subject: Re: T slot 3310
 Post Posted: Wed Sep 19, 2012 6:46 am 
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Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Hmm.....Now to start collecting thermoquads =;

Thanks again Shrinker its great to have you back so i and im sure others here can continue our educations!

Hysteric


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 Post subject: Re: T slot 3310
 Post Posted: Wed Sep 19, 2012 3:47 pm 
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Joined: Sat Jan 07, 2012 5:22 pm
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While digging through my archive of saved stuff i came across this post:

Guess it answers my question.

Quote:
Quality Idle Tips Fuel/Timing




By Shrinker,

The idle mixture screw should normally be around 1 to 1.5 turns out and the t-slot maybe .020" exposed up to .040", depends. If the IFR is too large and the idle air bleed too large then you have to restrict the idle mixture screw to get it correct at idle in neutral. When you put it into gear the revs drop a little and then the vac drops and then the flow restriction of the idle mixture screw has too much influence and it leans out and the engine dies.
The idle screw restriction needs to be so that it doesn't restrict it too hard and early as the revs slightly. The t-slot comes on very slowly at first and the idle has to make up the difference so that the mixture is consistent. If the mixture is set correct without using as much idle screw restriction the mixture from neutral to in gear will be more consistent, See when you use the idle screw you introduce a second restriction area; when there is only one as in the jet it works more consistently.
The Idle mixture screw needs to viewed as a fine trim adjustment not a dominant adjustment. You can then get a better balance from idle to t-slot because you don't have a large IFR jet that needs restricting to get a mixture at idle. When that happens the IFR feeds too much fuel to the t-slot so it goes rich on that. The amount of t-slot exposed at idle butterfly position influences the whole scene too. If you have too much fuel exiting from the t-slot you have to screw the idle mixture screw right in. Thats no good because then the engine runs too rich as the butterfly valve progresses up the t-slot. See the t-slot area is a jet as well.

A common reason for carburetor problems is the ignition timing is incorrect. If the engine runs too much advance too early it will seem like it needs less fuel and air but it wont pull a load so its useless. If the idle timing is too high you will screw in the mixture screw and it will run sweet but when you put it in gear it will die. So not all AFR problems are carby. You have to address all the things to get a tune going proper.


The basics are that if the timing is advanced too much you can lean out the mixture and more importantly you have to close the butterfly's. This makes it idle on not much air and fuel and then when you open the throttle it doesn't have enough fuel within the manifold to supply the cylinders. Fuel sometimes collects and sometimes dries out in the manifold on engines at idle, especially cammed ones and it makes it difficult sometimes to achieve what you want.
The vacuum of the inlet manifold determines the boiling point of the fuel, whenever you increase vacuum you lower the boiling point. As the throttle is opened the vac drops on some combinations, (others it can increase). If the vac drops the fuel remains more as a liquid and that liquid has to wet the manifold walls first. Once the walls are wet more fuel will make it to the cylinder. Thats basically what accelerator pumps are for. But when you only slowly open the throttle the accelerator pump doesn't work much so your relying more on the mixture from the t-slot.
If the t-slot is not exposed much in the idle position then not much fuel exits it at idle. It is possible that the t-slot is not flowing any fuel at idle and then when the throttle is opened fuel has
Quality Idle Tips Fuel/Timing




By Shrinker,

The idle mixture screw should normally be around 1 to 1.5 turns out and the t-slot maybe .020" exposed up to .040", depends. If the IFR is too large and the idle air bleed too large then

you have to restrict the idle mixture screw to get it correct at idle in neutral. When you put it into gear the revs drop a little and then the vac drops and then the flow restriction of the idle

mixture screw has too much influence and it leans out and the engine dies. The idle screw restriction needs to be so that it doesn't restrict it too hard and early as the revs slightly. The

t-slot comes on very slowly at first and the idle has to make up the difference so that the mixture is consistent. If the mixture is set correct without using as much idle screw restriction the mixture from neutral to in gear will be more consistent, See when you use the idle screw you introduce a second restriction area; when there is only one as in the jet it works more consistently.
The Idle mixture screw needs to viewed as a fine trim adjustment not a dominant adjustment. You can then get a better balance from idle to t-slot because you don't have a
large IFR jet that needs restricting to get a mixture at idle. When that happens the IFR feeds too much fuel to the t-slot so it goes rich on that. The amount of t-slot exposed at idle butterfly

position influences the whole scene too. If you have too much fuel exiting from the t-slot you have to screw the idle mixture screw right in. Thats no good because then the engine runs

too rich as the butterfly valve progresses up the t-slot. See the t-slot area is a jet as well.
A common reason for carburetor problems is the ignition timing is incorrect. If the engine runs too much advance too early it will seem like it needs less fuel and air but it wont pull a load

so its useless. If the idle timing is too high you will screw in the mixture screw and it will run sweet but when you put it in gear it will die. So not all AFR problems are carby. You have to

address all the things to get a tune going proper.




The basics are that if the timing is advanced too much you can lean out the mixture and more importantly you have to close the butterfly's. This makes it idle on not much air and fuel

and then when you open the throttle it doesn't have enough fuel within the manifold to supply the cylinders. Fuel sometimes collects and sometimes dries out in the manifold on engines

at idle, especially cammed ones and it makes it difficult sometimes to achieve what you want.
The vacuum of the inlet manifold determines the boiling point of the fuel, whenever you increase vacuum you lower the boiling point. As the throttle is opened the vac drops on some

combinations, (others it can increase). If the vac drops the fuel remains more as a liquid and that liquid has to wet the manifold walls first. Once the walls are wet more fuel will make it to

the cylinder. Thats basically what accelerator pumps are for. But when you only slowly open the throttle the accelerator pump doesn't work much so your relying more on the mixture

from the t-slot.
If the t-slot is not exposed much in the idle position then not much fuel exits it at idle. It is possible that the t-slot is not flowing any fuel at idle and then when the throttle is opened fuel has to be drawn through the drilling to get into the engine.


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 Post subject: Re: T slot 3310
 Post Posted: Fri Sep 21, 2012 10:45 pm 
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Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Shrinker, can an emulsion type carb be converted to a solid fuel type?

Looking at the AVS and AFB with the removable booster design would that not lend itself to modification?

Hysteric


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 Post subject: Re: T slot 3310
 Post Posted: Fri Sep 21, 2012 10:51 pm 
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Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
Like i said you can make anything into anything else. 'Solid fuel' types are difficult to tune because the fuel curve is set by sizing passages not easy to change parts like bleeds etc. If you just want to tune carby then stay with emulsion and learn how to use it minimally.


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 Post subject: Re: T slot 3310
 Post Posted: Fri Sep 21, 2012 11:40 pm 
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Joined: Sat Jan 07, 2012 5:22 pm
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Quote:
'Solid fuel' types are difficult to tune because the fuel curve is set by sizing passages not easy to change parts like bleeds etc


Is this how your Smart Carby works and why it takes time and possibly engine combo changes as the passages have to set according to the vacuum characteristics of the particular motor you build it for?

Tuning is one thing Shrinker but understanding the whys and hows to me is more important. :-$

I take it there are formulas to do all this?

Hysteric


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 Post subject: Re: T slot 3310
 Post Posted: Fri Sep 21, 2012 11:46 pm 
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Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
My smartcarby is a laminar flow carburetor which has no similarity at all to an emulsion carby or a 'solid fuel' carby. There is no comparison in tuning techniques.

The skill of tuning any carby is recognizing what the engine needs. Any carby can then be modified to accommodate the engine. To understand engines means to understand combustion and that requires some equipment, firstly a gas bench.


Last edited by shrinker on Fri Sep 21, 2012 11:57 pm, edited 1 time in total.

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 Post subject: Re: T slot 3310
 Post Posted: Fri Sep 21, 2012 11:56 pm 
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Joined: Sat Feb 07, 2009 4:12 pm
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Location: Adelaide Australia
EFI has just as many or even more issues with combustion than carbys do. Combustion control is not just about AFR management as most EFI people think, its about energy input to the fuel management. Power can be increased at exactly the same AFR by developing fuel input energy management.


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 Post subject: Re: T slot 3310
 Post Posted: Sat Sep 22, 2012 1:23 am 
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So Holleys,Carters, Webers etc. are all turbulent flow carbs?

Are we talking about the internal passages in the carb here?

Hysteric


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 Post subject: Re: T slot 3310
 Post Posted: Sat Sep 22, 2012 2:08 am 
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Joined: Sat Feb 07, 2009 4:12 pm
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Location: Adelaide Australia
Carburetors that use emulsion are turbulent flow designs. carburetors that use a booster or a single point sensing position for the air flow are turbulent flow designs. It is necessary to design for turbulent flow because of the vacuum curves relationship to CFM produced by single point sensing (boosters, single dump tubes like a C&S, old vintage carbys). There is nothing wrong with turbulent flow designs. They are quite capable of controlling a fuel curve in many ways. The solid fuel carbys are turbulent flow designs. Turbulent flow enables correction for the natural enrichment due to increased air flow. If an engine requires a different AFR at maximum torque compared to max HP then a turbulent flow carby can do that. The internal passages of a turbulent flow carby are sized so that the onset of turbulent flow occurs at the desired place in the CFM. Once turbulent flow is established the AFR goes leaner. Then as the CFM continues to increase the AFR will enrich. This creates the desired characteristics of lean cruise and rich full load combustion. If emulsion is not used the passage sizings are the only controllers and that means that the carby is specifically designed for that engine as in OEM production line stuff. If emulsion air is used the carby can have a wider range of application although theoretically none of the applications are as good as zero emulsion designing. The difficulty with emulsion is the air interrupts the fuel flow. Solid fuel designs achieve more linear fuel distribution into the air stream.


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 Post subject: Re: T slot 3310
 Post Posted: Sat Sep 22, 2012 2:55 am 
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Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Thanks Shrinker, I get it now!

Quote:
Fix a Holley and it will work like a Carter.


Hmmm....Looks like ill be the one sizing passages!

Thanks again Shrinker.

Hysteric.


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