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Carb Tuning

 
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John Hauck



Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

PostPosted: Wed Aug 26, 2009 3:05 pm    Post subject: Carb Tuning Reply with quote

Richard/Gang:

Took the liberty to change the subject line to reflect what you all are talking about. If we do that, when it comes time to search the Kolb List Archives for information, maybe we can find what we are looking for.

I assume you are talking about 912 carbs. These carbs operate on two static port sensors, one is the float chamber vent and the other is a port in the lip of the carb. These two ports compare static pressure and assist in positioning the piston in the vacuum chamber. I use air filter covers with the float chamber vent tube stuck in between the cover and the filter. Works pretty good.

If you have ram air impacting that port in the carb lip, it probably will upset the ability to read and compare static pressure correctly.

That's the way I understand it.

john h
mkIII



[quote]At Rotax classes I even asked Eric Tucker about my idea to put ram air into the carb throat and vent the float bowl to static pressure. Nope, can't do that either.

Rick Girard


[b]


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PostPosted: Wed Aug 26, 2009 3:36 pm    Post subject: Carb Tuning Reply with quote

That seems like a reasonable explanation to me.

Rick Girard
do not archive

On Wed, Aug 26, 2009 at 6:04 PM, John Hauck <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)> wrote:
[quote] Richard/Gang:

Took the liberty to change the subject line to reflect what you all are talking about.� If we do that, when it comes time to search the Kolb List Archives for information, maybe we can find what we are looking for.

�I assume you are talking about 912 carbs.�� These carbs operate on two static port sensors, one is the float chamber vent and the other is a port in the lip of�the carb.� These two ports compare static pressure and assist in positioning the piston in the vacuum chamber.��I use�air filter covers with the float chamber vent tube stuck in�between the cover and the filter.� Works pretty�good.

If you have ram air impacting that port in the carb lip, it probably will upset the ability to read and compare static pressure correctly.

That's the way I understand it.

john h
mkIII



Quote:
At Rotax classes I even asked Eric Tucker about my idea to put ram air into the carb throat and vent the float bowl to static pressure. Nope, can't do that either. �

Rick Girard




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dalewhelan



Joined: 11 Nov 2008
Posts: 105
Location: USA ARIZONA fountain hills

PostPosted: Wed Aug 26, 2009 6:04 pm    Post subject: Re: Carb Tuning Reply with quote

There are several ram air motorcycles with carbs that act the same way as the Bings on the 912.
In the motorcycle world they are called Constant Velocity carbs (CV)
Velocity in the venturi creates low pressure, there is a hole in the bottom of the slide (Piston) The low pressure lifts the slide against a spring pushing it down.
Here is the basics of the system.
The venturi and float bowls are both pressurized.
The fuel system normally uses a pump
One system pressurizes the fuel tank and then a throttles position sensor activates a solenoid to relieve tank pressure when the throttle is closed
Neatest systems I have seen have the whole carb in the airbox.
The power increase is not likely to be noticeable at 70 mph or so.
You are unlikely to see positive pressure at the speed we fly at but less negative pressure still does the trick.
Some drag race motorcycles (not sure of the class) use data acquisition and monitor Intake absolute Pressure. Not much happening till the speed gets pretty high.
Really only makes a difference at high speed high throttle opening.


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PostPosted: Wed Aug 26, 2009 7:54 pm    Post subject: Carb Tuning Reply with quote

My early experimentation with the suzuki included attempts to make a
mikuni CV carb work with it.
I spent too much time with poor results. I tried to educate myself
and varied as many elements as I could
but gave up and stuck the solex on. Too bad, it was (and still is) a
nice looking and lightweight contraption.

I never thought about fuel pressure requirements. ??????
BB

On 26, Aug 2009, at 10:04 PM, dalewhelan wrote:

Quote:

<dalewhelan(at)earthlink.net>

There are several ram air motorcycles with carbs that act the same
way as the Bings on the 912.
In the motorcycle world they are called Constant Velocity carbs (CV)
Velocity in the venturi creates low pressure, there is a hole in
the bottom of the slide (Piston) The low pressure lifts the slide
against a spring pushing it down.
Here is the basics of the system.
The venturi and float bowls are both pressurized.
The fuel system normally uses a pump
One system pressurizes the fuel tank and then a throttles position
sensor activates a solenoid to relieve tank pressure when the
throttle is closed
Neatest systems I have seen have the whole carb in the airbox.
The power increase is not likely to be noticeable at 70 mph or so.
You are unlikely to see positive pressure at the speed we fly at
but less negative pressure still does the trick.
Some drag race motorcycles (not sure of the class) use data
acquisition and monitor Intake absolute Pressure. Not much
happening till the speed gets pretty high.
Really only makes a difference at high speed high throttle opening.

--------
Dale Whelan
503 powered Firestar II
Projection, A simple and interesting Psychological concept


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