I suspect that my Jabiru 3300 motor is underpowered because it does not get up to the required RPM when stationary on the ground. I reach a maximum of 2100 rpm.

It has no measurable effect when using different propellers from the same manufacturer and identical length (Helix). I have tried propellers with 10, 11 and 12 degrees pitch and always the same effect, never more than 2200 rpm when standing on the ground.

Today I removed the air filter and the supply air now comes directly into the Bing carburetor, again without significant effect.
More RPM does not come from this.
It also doesn't matter if you turn on the additional electric fuel pump or not.

What else could it be and in what order do I best proceed to isolate the problem?
Too little fuel, possibly the wrong jetting, no or too little compression?

Does anyone have a suggestion for me please ?

Thank you and happy new year to you all.

Views: 1042

Reply to This

Replies to This Discussion


I had my cv bing apart about 6 mos. ago, and my mechanic carefully inspected the rubber diaphragm boot that controls the vacuum that pulls the slide.  He carefully stretched it and inspected it for tears and seating.  He said I should do this every time I have it apart.  

I’m throwing this out because it sounds like you have ample fuel flow, and you have a wide open throttle plate...  

Have you checked each cylinder while running at 2200 rpm?  Any shimmy?  All temps the same (using point and shoot thermometer)?  How did each spark plug look?

finally, let me add that I increased my mian jet only to start blackening my plugs and had to go right back to the leaner jet... so you’ll want to watch after you get your selection.

I’ll follow your progress, geo.

Maybe you already have solved your low power issues, but if not.
Check the diaphragm carefully, even a small crack in the rubber can create big problems.
In the 60s the Zenith/Stromberg carburetor was introduced in the automobile world. And it was just cracks in the diaphragm that created most of the problems.
The carburetor was produced under different brands, Zenith, Stromberg
 Solex, Pierburg and for BMW motorcycles the Bing. Later even used on Rotax and Jabiru.
I have replaced a lot of them on Saab and Volvo cars and also on a Grob 109 motorglider.
A typical issue with the Grob, was when engine didn´t rev up to 2800 rpm at full brake and load.
Remove top of carburetor and check diaphragm for cracks.
This thin rubber diaphragm can also be damaged in contact with gasoline and oil.

If you suspect any restrictions in inlet area, just compare the Static pressure with MAP, at full load.
Less than 1 InHg difference will not harm performance.
Also check difference in temperature OAT and airbox/inlet temp. Hi inlet temp will hurt performance.

Thank you for the reply. I am actually working on this issue.

As you can see I got all the spare parts an will replace them now.

Is there any chance to see or control if the membrane is fittet properly and air tight ?

Check for any small hole or crack in the old membrane. Any leakage will prevent to lift piston enough. And airflow will be restricted. Engine will not rev up.
The two tabs are holding membrane in positon.
The membrane on my photo had two small cracks, but I have also seen a 25mm long opening on one another.

Hi. I found a site that have a lot of photos inside the Bing carb. Maybe useful?
I am most familiar with the Solex 150, but membrane from Bing fits even on this. BMW part 13111254774.


What prop
And prop
Pitch do you have?
R u getting full theottle throw?

So, the whole Saturday and Sunday screwed on the plane, while the others flew in perfect sunshine.
Now I am with my Latin at the end and rather desperate.
The Bing carburetor was disassembled cleaned and all seals renewed.
The gasoline supply is tested and more than sufficient.
The gasoline is fresh from the gas station.
The engine has fresh oil and a new oil filter.
BUT with the 12 degree propeller it still only makes 2200 rpm.
I changed to the 11 degree helix propeller and get just 2400 rpm.
The test runs on the ground were with open air intake without filter. I used a scope to observe the air intake and the vacuum can in the Bing carburetor opens the airflow at full throttle completely correctly.
It does not change the RPM if the second electric fuel pump is engaged.
What can be the problem? What else can I check?
Can it be a problem internal to the engine with too much friction ?
Who else has an idea for me ?
Thanks to all.

What are the exhaust temperatures?

In your photos of the main jet, jet carrier, needle jet... Where is the atomizer as pictured below?

Carburetor Bing pre atomizer

If I recall correctly that atomiser can be replaced upside down - something else to check

Hi Steffen
You really have had more than enough problems.
I don´t know if you have an old used or a completely new engine. But I think you have to start with very basic investigations.
I would start with Leak down test, to be sure you have no leaks in valves or cylinders.
Check all sparkplugs and wires.  
Measure the resistance in all ignition wires.
Are the ignition timing up to spec?  My guess around 25 deg BTDC.
Inlet manifold, look for leaks, can you see any damaged gaskets or not connected vacuum hose?
If MAP and static press (at wide open throttle) are close there are no restrictions.
Is temperature OAT and inside air box close to equal, no problem.
Air-fuel ratio, you can use CHT and Exhaust temp, to see difference between cylinders.
But to identify too lean or rich it is better to check with a Lambda instrument.
I use an Innovate MTX, low price- good quality. Guess you can buy the kit for 200 EUR. Bosch 4.9 sensor included.
Lambda values, at takeoff 0,92-0,94 (rich) and at level flight close to 1,00 (normal). Above 1,05 far too lean.
If you use an EFIS, the logfile can help you to understand more, if all temperatures seem to be all right, oil and fuel pressure are up to spec. Rpm and MAP that works together.


thank you for the reply, Measuring the pressure for leakage ist the next step.

It is an unused but new-old engine, about 12 years in the box and now has about 20h running time.

I re evaluated the air intake side and fuel side now completely and changed a lot.

But still max rpm 2500 even running the plane 80-90 kph on the runway.


New from Zenith:

Zenith Planes For Sale 

Classified listing for buying or selling your Zenith building or flying related stuff...

Custom Instrument Panels
for your Zenith

Custom instrument panels are now available directly from Zenith Aircraft Company exclusively for Zenith builders and owners. Pre-cut panel, Dynon and Garmin avionics, and more.

Custom Upholstery Kits for your Zenith Aircraft:

Zenith Vinyl Upholstery Kits

Zenith Apparel from EAA:

Zenair Floats

Flying On Your Own Wings:
A Complete Guide to Understanding Light Airplane Design, by Chris Heintz

Builder & Pilot Supplies:

How to videos from HomebuiltHELP.com

Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit HomebuiltHelp.com for the latest DVD titles.

Aircraft Insurance:


West Coast USA:

Pro Builder Assistance:


Transition training:

Golden Eagle Aviation

Pianosa Flying Farm

Aircraft Spruce & Specialty for all your building and pilot supplies!

© 2021   Created by Zenith.Aero.   Powered by

Badges  |  Report an Issue  |  Terms of Service