Bing 64 carburetor

[David Ames]

I have a Savannah with a Rotax 912.  It has been running rough after take off.  I tried using a little choke and that smoothed it out.  Checking the plugs they are all consistently white insulators.  The needle is the third from the top.  The main jet is a 155.  The float level is ~10 mm from the top of the bowl.  Any ideas?

[Kiwi]

Check that the vents from the carbs to airbox are connected and not leaking. 

Edited July 4, 2022 by Kiwi

[IBob]

What is the history, David?

[spacesailor]

Also  those little rubber caps on the side of the carbie .

spacesailor

[David Ames]

The vent tube to the airbox are free flow and positively attached.

Not sure about the rubber caps.  I do not see any on the Bing 64.

Not sure how to answer the history question.  The engine went "on condition" last November so the plugs fuel pump and rubber parts were replaced.

[IBob]

The history question:

Have you owned and flown the aircraft for a while?
If so:

Has it always done this or did it just start to do this recently?

If it started recently, was it a slowly deterioration, or did it just suddenly start to happen?
And, most important:
What, if anything, was done by way of maintenance or adjustments in the the engine bay before or around the time that this began to occur?

 

Also:

Were the fuel filters changed at the same time as the rubber replacement?

And are you seeing good (2psi+) fuel pressure at all times? (But bearing in mind that the current Savannah fuel filter arrangement has one filter before the electric pump, but 2 filters to the respective carbs, which are after the fuel pressure reading is taken.)
 

[David Ames]

Pressure is ~5psi.  Fuel flow at the carbs with the electric fuel pump is >50 liters/hr.  Only have one fuel filter between the tank and electric fuel pump.

The symptoms are not consistent.  Though more recently.

[IBob]

Have you weighed the carb floats as per the Rotax spec?

Rotax seem to have gone through an astonishing number of float versions, possibly one of yours is marginal (though I would have expected that to show up at low power settings).

 

It certainly sounds like a fuel problem, have the carb rubbers and seals been replaced?

[David Ames]

Floats were weighed.  Bowl level is ~10 mm from the top.  Needle diaphragm and cuffs replaced.

I am thinking it is running on the lean side.

[IBob]

Diaphragms and cuffs replaced before or after problem emerged?

And when you said runs rough after takeoff, can you be more specific? Is this when you throttle back to cruise? And if so, how does it run on all other modes of flight and idle etc?

 

[IBob]

Hi David, did you manage to isolate the problem?
Interested to know what you may have found.......

[David Ames]

I am trying the needles at the fourth notch from the top. (it seemed like the easiest and least intrusive step)  I have only done one static test run.  I ran the engine for ~ 15 minutes at various throttle setting (sometimes at 5600, the prop wash was impressive!).  I slowed the engine down taking ~15-20 seconds and shut it down.  After I let the engine cool I checked the top 4 spark plugs.  Front plugs were sooty.  Back ones slight color to white.  Before changing the needle all the plug insulators were white.

I will be doing flight tests when the weather gets better.  

[facthunter]

That manifold set up will always produce uneven mixtures. It's normal to do that. Nev