3300 Jab problem

[Rick524]

When I do a static full power run-up, my engine is stopping when I reach full throttle. It starts
and idles fine and the rpm smoothly increases as I advance the throttle, until 2650 rpm, then sputters and coughs and will
stop if I don't throttle back to under 2600 rpm.
I have a Bing carb and Sensenich W54SK64G prop, field elevation is 1650'. I've tried both the normal fresh air
input and the carb/alternate air input from the cowl, no change. My fuel pressure sensor in the line just before
the carb reads 3.7 psi +/- .3 psi all the way from idle to full power.
Dont know where to start. The only thing I can think of, is possible air turbulence at the carb input and might try
putting an air straightener into the rubber elbow before the carb.

Any suggestions are welcome.

Rick
Sonex 524

[fastj22]

This is a problem typical with an Aerocarb not a Bing. Look at fuel flow. Seems its running out of go juice at higher demand. What is your fuel flow prior to the carb? (disconnect at the carb and measure the flow.)

[Rick524]

Thanks John, I did a fuel flow test last summer with just the engine mounted pump and it passed. I'll go out tomorrow
and do another flow test. It does seem like the bowl is going empty at high rpms.


Rick

[tx_swordguy]

Just a thought. It sounds like a fuel starvation issue. Is there a filter of any kind AFTER the fuel psi sensor? Maybe its clogged enough to slow down fuel flow.

[Rick524]

Hi Mark, no fuel filter after the pressure sensor. The sensor is only 6" from the carb fuel input. Seems odd that the
pressure is 3.7 psi at the sensor, but the bowl is going empty, (if it actually is). Could be some sort of obstruction
in the hose to the bowl I guess.


Rick

[sonex892.]

Hi Rick
Sounds like it could be the mixture going nuts. In addition to checking fuel flow, there are a few other simple things you could check.

Does it behave the same with the cowl on and off?

Is the choke shaft fully off?

Is the carby balance tube connected to the clean air side of the air filter?

Is the float level set correctly? Level the engine and prime the carby bowl, turn off fuel then remove the bowl. Should be a 12 mm gap from the top of the lip on the bowl to the fuel.

If all those check out ok. I would then be looking at the possibility of turbulent air messing with the mixture. Air straightener or cobra head might be required. These are a great carby but they need smooth air to operate. A close elbow or scat tube has been known to make them run rough at high power. My first Jabiru installation was in a Sonerai. It turned out to be a great example of what not to do for an induction system for the bing. Scat tube and elbows. It took a relocation of airbox and total redesign of induction system to get that one to work.

Myself I would phone and ask Jabiru. They know these things better than any of us and Jabiru Australia are always very helpful.

Good luck
Steve
Sonex 892 Jab 3300/bing

[DCASonex]

You mention trying both fresh air and alternate air from cowl inlet. Bing carbs can be fussy as to just where the sense tube is placed, and they do not like ram air. Assuming you have EGT monitoring, check that for clues if running too lean. If problem not quickly found might try mounting an air filter directly on the carb inlet and running the sense tube into that filter. If that works, then you will know problem is in intake system.

David A. CAMit 3300.

[tx_swordguy]

Is this a flying airplane that recently started doing this? or a new build prior to first flight? How are the mag drops? It may be as simple as a lean main jet. At 2600 you are getting fully into your main jet. If it is a new set up I would get a main jet on either side (one up and one down) from your current main jet. It may be going lean or rich when moving into the main. I would think lean but if it is super large main when it moves into the main range it could be drowning it in fuel. My experience with the bing is in a rotax 582 2 stroke but the carb acts the same between 2-4 strokes
Mark

[N190YX]

Does the Bing have a high speed jet and a low speed jet? if so, perhaps the high speed jet may somehow be compromised (clogged with foreign material or defective, etc.).

[Rick524]

Thanks for all the suggestions!
I'll answer some of the questions:

The plane has never flown, we discovered this problem just before the first flight attempt...thank goodness.
It does the same thing with cowl on or off.
I measured the fuel level in the float bowl and it is 12mm from the bowl lip.

Results of flow test from this morning:
-Tank half full, plane level, measured at hose to carb input.
-Boost pump only, 1.7L @ 1 minute
-Mech pump only, .5L @ 15 seconds = 2L/min
-Both pumps, .5L @ 15 seconds = 2L/min

Even with just gravity feed, there is a good flow (didnt measure it). Seems to rule out a fuel delivery issue.

These are the numbers engraved into the side of the carb:
M255/N285 Needle LA13940D-2
3300 23547

Couldn't do a runup today, but didn't really change anything so doubt theres any improvement.
I think Ill plan on moving the sense tube next and look at making an air straightener.

I'd like to put up a picture of the carb/air input/filter box, but not sure how to do it. There may
be something obvious I'm missing.

Rick