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Concentric Float height #48211
07/11/06 11:40 pm
07/11/06 11:40 pm
Joined: Aug 2003
Posts: 79
Sydney, Australia
M
Mebbo Offline OP

BritBike Forum member
Mebbo  Offline OP

BritBike Forum member
M
Joined: Aug 2003
Posts: 79
Sydney, Australia
This is going to sound silly, but I really am having difficulty understanding certain operations of the AMAL Concentric - Mk1 anyway.

Reading lots of posts and instructions re the importance of float height to lean or rich running, I don't understand. From what I can see of the diagrams etc for Concentrics, the takeoff from the float chamber for both idle and open running is near the base of the chamber.

As long as the float needle is shutting off the intake to the chamber before the bowl floods into the carb moth (could it do that, or just pour out the tickler?), I would have thought it wouldn't matter what the float height was as long as enough fuel was available to the jets to sustain running.
The carb jets and manifold vacuum control how much fuel gets into the bore of the carb to mix with air, don't they? No more fuel can get into the mixing chamber than is allowed by those jets and the engine vaccum. Isn't the float chamber just a reservoir to provide sufficient fuel for the carb??
I could see that the if the float height were way too low, the carb might starve at full bore, but otherwise how can the fuel level in the chamber influence running?? How can the level affect the metering of fuel to the carb if the intakes are at the base and the jets/needle/vacuum control the flow?
Please educate, I'd love to know the answer!
Mebbo

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Re: Concentric Float height #48212
07/12/06 4:05 am
07/12/06 4:05 am

A
Anonymous
Unregistered
Anonymous
Unregistered
A


Too many thousand words required.
Try "venturi" and "head of pressure" in google.

Re: Concentric Float height #48213
07/12/06 6:42 am
07/12/06 6:42 am
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Tiger Offline
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Tiger  Offline
BritBike Forum member
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Think "suction lift".


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: Concentric Float height #48214
07/12/06 7:53 am
07/12/06 7:53 am
Joined: Aug 2003
Posts: 79
Sydney, Australia
M
Mebbo Offline OP

BritBike Forum member
Mebbo  Offline OP

BritBike Forum member
M
Joined: Aug 2003
Posts: 79
Sydney, Australia
Ahhh..Bernoulli's equation!
Thanks for the pointers.
That small height difference between the float level and the floor of the venturi can affect the flow velocity and therefore fuel volume from the outlet even if the venturi pressure drop is held constant.
the marvels of Google!

Mebbo
'70 Lightning
'74 850 Commando
'48 B32 (in bits)
'49 ZB34 Gold Star (in even more bits)

Re: Concentric Float height #48215
07/13/06 12:36 pm
07/13/06 12:36 pm
Joined: Oct 2003
Posts: 11,222
North Georgia, USA
RF Whatley Offline
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RF Whatley  Offline
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Joined: Oct 2003
Posts: 11,222
North Georgia, USA
Yea. Like they said.

If you were drinking burbon through one of those tiny, tiny straws, like a coffee stir stick, then believe me, you'd want to start with the liquid level near the top. Don't ask how I know this.


laughing


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: Concentric Float height #48216
07/13/06 11:39 pm
07/13/06 11:39 pm
Joined: Mar 2005
Posts: 10,157
Boston, Massachusetts
J
John Healy Offline
BritBike Forum member
John Healy  Offline
BritBike Forum member
J
Joined: Mar 2005
Posts: 10,157
Boston, Massachusetts
Very simply put...
We are surrounded by air pressure. Approx 15 pounds per square inch at sea level. It is pushing on everything, including the gas in your float bowl.

Now you need a way to lift this gasoline into your inlet port. It won't go up there itself, even with the air presure pushing on it. But, create a vacuum in the inlet port and the differential in the air pressure (ambient air pressure pushing on tthe top of the gas in the bowl) vs. negative pressue in the port) and you can lift the gasoline up through the jets.

Remember that old saying: "Nature abhors a vacuum."
Well carburetros work on ambient air pressure, the air around us, and manifold vacuum. The higher the gasoline in the the less vacuum needed to lift it.

The higher the gas is in the bowl the less difference in pressure, or energy, required to lift the gasoline. As Panic suggests google venturi (venturis create vacuum).



Moderated by  Alan_nc 


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