Author Topic: Jabiru 3300 engine  (Read 643 times)

Bil438

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Jabiru 3300 engine
« on: Mar 02, 2017 »
This is part of the engine conversion and Hoerner wing tip mod for my S IILS.
Today I worked on the switch panel to set up the electric carb heat. Because I have cowl flaps I wanted to reduce the number of mechanical controls in the cockpit and through the firewall. 

The Carb is a Bing 40mm ordinarily standard for the Jab 3300 engine. I believe the carb heat kit come from the UK. It's a single cylinder about 2" L X maybe 1"D. bolted to the side of the carb. It has 2 electrical studs.

It may be overkill because the Bing Carbs are constant depression carbs, i.e they don't really have a venturi in the throat. Hence icing conditions must be heavy before ice will collect in the carb. In 7 years I've never actually had carb ice. I fly spring, summer and fall.

So the carb heater module described above is bolted in place. I was at a loss to remember the carb heat wiring. But a VOM tester showed each heater coil to have a resistance of 7 ohms. That simplifies it. The switch is a DPDT (Double Pole-Double Throw) switch wired to bring 12VDC to the aft terminal on the heater, which means say 2 amps. Since I=E/R, then the current is 2 amps and that is say 28 watts.
So the switch:ON-OFF-ON is switched down and one coil is heated. They call this carb anti-ice.

Two wires are connected to the Up connections on that DPDT switch, they are brought forward to the carb heat module on the carb. One wire is connected to the Fwd Terminal and the other is spliced to the aft terminal. With UP selected and A VOM tester used the +12V contact is tested to ground and 14 ohms is indicated. That's exactly what's wanted.

Thus is you had carb ice you'd select the switch up and both coils would heat. That's say 56 watts. Presumably that's enough to melt ice in the carb with the engine running say on approach. Thus with the switch up you have carb de-ice.

Fuse- I'll try it with a 5 amp fuse but if it doesn't last i could go to either 7.5 or 10 amps.

I'll get a photo and try to get it uploaded to this site.
Bill 438

Bil438

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Jabiru 3300 engine-carburation
« Reply #1 on: Jan 10, 2018 »
I pulled the float valve seats from both the installed and spare Bing 94 carbs. Turns our the new J2200 engines use the same carb body as the J3300s but with all different brass parts. The float valve seats are pressed in and not usually replaceable but I made up a slide hammer for 5/16 threaded rod, tapped the seats and pulled the seats out.
One was replaced with a .100" seat and the one with the regular 3300 jets with  a .145" seat.
One thing that gives me pause is that the float valve is engineered to limit the fuel coming into the bowl at say 3psi to just enough fuel to power the engine to it's max RPM. If you open the butterfly beyond takeoff  power then engine falls flat on it's face. If the throttle is not quickly closed the engine stops.
I'd tried everything else and when nothing else helped I was left with no choice but to change the seats.
The advantage is that one cannot take the engine beyond it's rated max rpm. The other is that if the float valve stuck open or leaked it could never leak more than the fuel used at takeoff.
I'd installed larger main(takeoff ) Jets so I need to return them to standard Bing #285 main jets.
The various carburetors/injectors you guys use, exactly what limits takeoff RPM: Fuel pressure, float valve, main jet, carb throat size, solid lifter spring float, Propeller DIA and Pitch dia?
Bill E

Pttim

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Re: Jabiru 3300 engine
« Reply #2 on: Jan 10, 2018 »
On mine with the Aerocarb, it is my absolute static RPM that is the limiter.  Less in winter due to denser air.
Pttim
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Bil438

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Re: Jabiru 3300 engine
« Reply #3 on: Jan 15, 2018 »
In the world of Jabiru engines, it's the propeller that limits RPM and I expect everything else is tuned to suit Static or Max RPM. On my Bakeng Deuce, the Lycoming is limited to 108 hp but 115 in level flight full throttle for 15 minutes.

The thing that threw was the Bing Carb float valve which is set to admit just enough fuel to get 2750 rpm full throttle. Thus the main and needle jets and prop are chosen with that in mind. I can see why. The carb could never leak fuel at full throttle as it burns all it gets.
The flip side is that any tiny debris or tiny fly in the float valve restricts takeoff power. Hate that as I once found a fly in the float valve. That's also why I run fuel filters/screens at every component.
BillE

 

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