bing carb ?

[tx_swordguy]

I currently have an aeroinjector on my jab 3300. I have been piddling with the carb for over a yr. My biggest problem may have to do with the intake manifold (that I have not gotten into) but it is on take off (initial, not as bad on T&G) my #6 cyl will climb over 1425 EGT if at full rich and full throttle. I usually back off and climb at 2850-2900 rpm and 100 mph. The lower throttle will drop EGTs into 1300 range. I have resealed the #6 intake thinking it may be an intake leak and that has not solved the issue. On initial take off #6 can easily be 50 degrees or more above the next closest cyl EGT. I can cruise at 2650 and lean 1,2,6 to the mid 1350ish range and 3,4 in the lower 1200s and 5 will be in the high 12s. This is with mixture over an inch pulled out on a #3 needle. I feel my numbers should produce a pretty lean mixture. I just pulled my plugs and all were dark and quite rich (this is with a hotter plug D8ea) I have been doing a lot of T&G so there has been a lot of full rich to lean mixture movements, but cruising is always as lean as I can get it with the goal of 1350 EGT. I have not tried the 2.5 needle but have tried the 4 and the 4 was just horrible. I am at the point of thinking a bing may be on the horizon. My question is can I use only an electric fuel pump with the bing? I do not have a mechanical fuel pump currently and would rather not have to buy one if at all possible. I may be willing to try a 2.5 just to see what happens but am not thinking it will help the issue. The engine runs well but I don't like pulling plugs out and seeing them covered in black powder lol. I will try going WOT in level flight and see if I can lean out mix but tried it once before and my EGTs went higher not lower. Because of that I am not looking like the 2.5 will help that is why I am looking at a bing

[fastj22]

I've seen the same. On take off and climb, my #6 can go very high on EGT, but in cruise everything levels out.

The Rotec carb I tried really helped this, but I wouldn't recommend it based on a bad experience.

I really think its about atomization of the fuel. The Aerocarb is pretty crude and just dumps fuel into the throat. The fuel/air don't have much time to mix before the quick bend to #6 and the result is a lean mix for that guy. The Rotec uses a spray bar which better atomizes the fuel. The Bing, being a venturi carb, also does it better. I know one sonex guy that simply loves his Bing on his sonex/jabiru.

When converting to the B-model, I considered remotely mounting the aerocarb via a snorkel further away from the intake, kinda like how the turbos work. But just couldn't figure it out. So I'm back to where you are.

One thing though, is your carb mounted vertically? So the pull is either up or down, not side to side? If its side to side, no go. It really effects the feed to the back cylinders.

[peter anson]

Just to answer the original question about fuel pumps with the Bing, I can't see any reason why the Bing wouldn't work satisfactorily using only gravity feed as long as you can ensure sufficient fuel flow with just gravity. Having said that, I use two fuel pumps in series; the original Jabiru mechanical diaphragm pump and an SU electric pump which is also a diaphragm type. The SU pump is heavy, and I seem to recall fairly expensive, but has been totally reliable. It was installed over 7 years ago and I usually leave it on all the time.

Regarding the wide difference in EGTs, my Sonex has similarly large differences although nowhere near as high. The #5 is easily the highest at about 740°C (1364°F) on climb, easing to around 700°C (1292°F) on cruise. All the other EGTs are in the 625 - 650°C range. I think one of the changes made by Jabiru to the inlet manifold was to replace the little airfoil shaped spacer with two round cylindrical spacers which was supposed to cause a bit fo turbulence and vapourize the fuel better. I haven't bothered to make that change. My engine runs fairly cool and since having a discussion with Jeff and the guys for the Sonex podcast have changed to D8EA spark plugs, one step warmer than standard. They still come out looking pretty dark but again, I have never experienced any problems with fouling.

Peter
Sonex 894 - 440 hours
Jabiru 3300 Serial #116

[builderflyer]

I currently have an aeroinjector on my jab 3300. I have been piddling with the carb for over a yr. My biggest problem may have to do with the intake manifold (that I have not gotten into) but it is on take off (initial, not as bad on T&G) my #6 cyl will climb over 1425 EGT if at full rich and full throttle. I usually back off and climb at 2850-2900 rpm and 100 mph.

Mark,

You're not alone with your EGT operational experiences. I've been flying my Sonex for over 14 years, first with an AeroCarb and now with an Aeroinjector and having excessively high EGTs on the 2 back cylinders (#5 is worst for me) is commonplace during climbout or during full throttle operations. But to achieve a Jabiru required maximum of 1256 degrees at high power settings is impossible on the back 2 cylinders, regardless of what needle is used. I've always found that a 2.5 needle is best for my engine in that it provides the smoothest running engine at any power setting. As you said (and others will say the same), it is necessary to throttle back a bit to bring the back cylinders EGTs down somewhat and my target has been to keep them below 1350 degrees, not the unattainable 1256 mentioned above. Having so much excess horsepower with the 3300 engine, throttling back in a climb isn't a real issue.

The plenum and not the carburetor seems to be the real problem on the older engines. One thing I've done is to replace the airfoil shaped splitter with a round one and this has helped a little to bring the EGTs closer in line with each other but not to an acceptable degree. Some day I'll try a larger diameter splitter in order to direct a bit more of the fuel to the rear cylinders......some day.

I believe John Monnett saw this same issue on the prototype Sonex with the 3300 engine. There was a time he encouraged us to not measure the EGTs on the back 2 cylinders, only the front 2 cylinders. I flew my plane in that manner for quite a while and I have to say my engine never ran better (tongue somewhat in cheek) at the same time my anxiety level remained unusually low. Sometimes we have too much information for our own mental wellbeing and despite this EGT matter, my engine continues to run well.

Art,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[sonex892.]

With the fuel pump question, I, like Peter see no reason gravity feed would not work with a bing. I do know with the mechanical pump in the circuit, it would not work without a check valve. With gravity only a dribble flows through the mechanical pump, that is why I use the backup pump. If the mech pump fails its going to starve of fuel the facet will pump through the mechanical pump. In over 400 hrs I've never really used the electric pump in flight. I test it works prior to starting to prime the bowl in the bing only.

As for EGTs mine are best at economical cruise settings. At WOT they go higher the hottest cyl will climb to 720 deg C. Being a constant velocity carb they do vary with different altitudes vs cruise settings. The Jab factory told me years ago to install a manifold pressure gauge as the MP gauge, not the RPM's will show how much power is being produced. 19" MP is always 19 Litres per hr. At 1000' ASML Its not uncommon to see 19" at 2400RPM and 23" at 2700 RPM. If I climb to 5000' it would probably be 19" at around 2700 RPM.

[142YX]

The Bing should absolutely work with gravity feed, one electric pump, or multiple pumps. The only thing the system cares about downstream of the fuel inlet to the carburetor is that there is fuel in the bowl, and that there is a delta pressure between the bowl and the throat so that the fuel can be sucked into inlet manifold at the appropriate rate (which is pretty sophisticated on the Bing, as an altitude compensating carburetor, but is in no way affected by the upstream fuel system pressure). Therefore, the only thing that the pumps (or gravity) really do is re-fill the carburetor bowl, as controlled by the bowl float valve.

So the questions you have to ask yourself are:
1 - what is your confidence level that your system provides adequate gravity feed flow rate in all flight regimes?
2 - what level of redundancy are you comfortable with?

My own personal experience below, so take it with a grain of salt..

The first two flights of my Jabiru 3300 powered Waiex were done on the Aeroinjector/gravity feed fuel system. Things ran reliably but very rich. I was unable to develop full power (I could only get 2800~2900 rpm). The blerb I wrote shortly after my first flight when the details were fresh in my head:

After reaching about 5,500 feet I began to lean the mixture in an attempt to get more RPM. I noted somewhere around this time that the fuel flow was indicating 10.4 gal/hour which is near what it should be for full power, however I did not think I was developing that and it lead me to believe that I was rich. As I turned the mixture knob back, RPM did respond by increasing (I believe I saw over 3,000 RPM) however exhaust gas temperature rose sharply into the red and I noted some temperatures in the mid-to- upper 1,400 °F’s. This made me push the mixture back in until EGT turned green again and leave it there for the remainder of the flight.

I messed around with the settings in the Aeroinjector between flight #1 and #2 but I didn't see much improvement in RPM/Power. EGT’s on #5 and 6 were ~60F above the highest other cylinder (#4) and ~80F above the average of the other 4. Messing around with things post flight #2 on the ground just frustrated me, and I gave up on the Aeroinjector, deciding I did not like the design and the annoyance of the adjustment process. I spent the next several weeks installing a Rotec TBI setup.

At some point during that process I did a gravity feed flow-rate test and found the performance to be marginal at best, failing the standard 1.5 x max flowrate rule of thumb (I got only 12 gal/hour at half tank level, and only ~9.5 gal/hour in the last gallon). Thinking that the ground-attitude at which the test was performed may not even be the most conservative (eg, extreme nose-high attitudes seen in flight) I decided I wasn't comfortable with gravity-feed only, so I re-installed the mechanical Jabiru fuel pump. Now, I do have a red-cube fuel flow transducer in my system, as well as an in-line filter AND a gascolator. There are others with simpler fuel systems with fewer flow restrictions, maybe the flow is sufficient in those applications. I also was not comfortable with having a simplex fuel system where a failure of the mechanical pump would result in a loss of power, so I added an electric pump in serial, upstream of the mechanical pump as well (I chose the Jabiru USA recommended Facet 40105, $40 from aircraft spruce). In flight, I turn on the electric pump for takeoff and landings but turn it off in cruise.

The Rotec TBI did not end up working out for me, actually the engine quit on the first takeoff roll for an attempted flight #3. Admittedly, I think this was my fault, having the TBI set up much too-lean. When I contacted Rotec for advice, they admitted to me that there was also a regulator valve-seat “design improvement” that I should be using (and I was provided the upgrade parts for free), but this freaked me out a little bit – so I just put the Bing back in.

Since then, the Bing has been outstanding. Trouble free, with no drama. I was a bit annoyed that I wasted so much time messing around with the other-than-stock setup, but I guess I learned something in the process? I live in Colorado now, and the Bing does run way too rich at high altitude/high power settings.. so I added a Hackman mixture control which dramatically improves performance with the Bing at high altitude. Originally, I was very motivated to try the TBI again, but to be honest fastj22’s experience with the TBI and my own motivation to focus on some other projects have prevented me from doing so. The Bing/hackman, dual-fuel-pump setup with wide band AFR sensor situational awareness has been outstanding, and I will probably never change it as long as I am flying behind a Jabiru. My current EGT spread between 5&6 and the next highest/average is about half of what it was with the Aeroinjector at about 20/40F. The TBI has better atomization than the Bing, which has the potential to unlock a bit more power and even more level EGT’s.. but it does not seem worth it to me to mess with it any further after 350 + trouble free hours with the setup I got.

Sorry for being long winded, but hopefully the context helps. I would say that in a very simple fuel system (no fuel flow sensor, maybe only a single filter), with promising results from a ground fuel flow rate test, a gravity-feed only system feeding a Bing might be fine. However, if gravity only is not enough, having a single pump (mechanical or electrical) exposes the fuel system to a single point of failure. Having two of one type exposes the fuel system to a common mode of failure (think electrical system failure making the otherwise perfectly good engine turn off). IMHO, one mechanical and one electrical is the best setup.