High Idle Speed - SOLVED AT LAST

The Bell crank has a lot more effect than the air bleeds, effects all the way from zero to full throttle.
If both butterflies are the same there should be no reason open an air bleed
The Stepper will make the idle speed correct.

At the moment mine seems to idle within a few inches WC with no air bleed.

XU12 wrote:

One Question from my poor understanding:
How will affect this the synchronisation of the System above idle? If the right hand butterfly has to be more opened to achieve a good synchronisation measured by dp??
So i have to choose between normal idle revs or good synchronsation at 4000 rev?

No. There is no reason not to have one air bleed open to achieve balance at idle and at 4000 RPM.

Kiwi_Roy wrote:

The Bell crank has a lot more effect than the air bleeds, effects all the way from zero to full throttle.
If both butterflies are the same there should be no reason open an air bleed
The Stepper will make the idle speed correct.

At the moment mine seems to idle within a few inches WC with no air bleed.

A few inches? Then you've got a compromised system. I can get mine balanced within 1/2 inch or better, and have no idle problems.

Thanks for your answers. This Weekend i take a lot of time to check and balancing the system at 3000, 4000 and 5000.
now both air bleeds are closed and idle is normal. CO trim moved from -4 to + 3 for better run of engine.
It is now cold in germany with only 6-7 °C and the test drive was short, but now very great run of the engine thanks to beetle's map.

beetle wrote:

XU12 wrote:

One Question from my poor understanding:
How will affect this the synchronisation of the System above idle? If the right hand butterfly has to be more opened to achieve a good synchronisation measured by dp??
So i have to choose between normal idle revs or good synchronsation at 4000 rev?

No. There is no reason not to have one air bleed open to achieve balance at idle and at 4000 RPM.

A few inches? Then you've got a compromised system. I can get mine balanced within 1/2 inch or better, and have no idle problems.

[/quote]
1/2 an inch using what?

I'm talking inches of oil actually, less than a kPa, 1 hundreth of an atmosphere, a knat's cock, 5/8th of FA

You are right there is no reason not to have one open, I'm just saying you don't need to get it any closer than a few inches WC, thats a very small error.

XU12 seems quite happy with his.

Kiwi_Roy wrote:

The Bell crank has a lot more effect than the air bleeds, effects all the way from zero to full throttle.
If both butterflies are the same there should be no reason open an air bleed
The Stepper will make the idle speed correct.

At the moment mine seems to idle within a few inches WC with no air bleed.

Just an observation I discovered with my stepper

I have a circuit to drive the stepper open or closed that I used to test it a while back and I found, if driven to the closed position and I blew in the inlet port, one side passed air and the other didn't.

You could therefore possibly assume, that at idle there's a good chance that the  stepper wont be passing air evenly to the TBs necessitating opening an air bleed to even things out

At 3k I think that the stepper should be fully shut (Beetle can confirm I'm sure) and any air bypassing via the leak stepper is inconsequential