Bing carb problem

[Rick524]

I have a 3300 with Bing carb that I just started and ran last week for the first time. It started and ran
good except I noticed some black exhaust at idle. I took the plugs out and they are all black and sooty.
Then I noticed the map tube to the rdac and balance tube had gas in them.
I briefly cranked the engine with the throttle at idle, choke off and no plugs and gas was pouring from the balance tube.

I took off the float bowl, which was full, to see if the float was stuck, it isn't.

Has anyone had this happen? My best guess is the float needle isn't stopping the fuel from the
pump.

Rick
Sonex 524

[sonex892.]

Hi Rick.

The float level may need adjusting I'd check that first. After removing the bowl measure the distance from the top lip of the bowl to the fuel there should be 12mm.

The fuel in the balance tube may have created an airlock stuffing up the mixture metering.

Too much fuel pressure from an fuel auxilliary pump?

page 63 https://jabiru.net.au/wp-content/upload ... 0002-7.pdf

[Rick524]

Hi Steve, thanks for the reply. I removed the float bowl and held the float up, while my wife
cranked the engine over. No gas pumped out until I let the float drop. I removed the carb from the engine for a closer look. I put a hose on the gas nipple and blew while cycling the float up and down. All good.
I tweaked the float down slightly and re-assembled. Then I connected the fuel line to the carb and while
I held it, my wife cranked the engine......no leaks.
I re-installed the carb and will try it tomorrow. Sure hope it works, everything smells like gas around
here, including me.

Rick
Sonex 524

[DCASonex]

If black soot at idle, do not overlook the most obvious. Crank in the idle mixture screw on bottom of carb, then back out about 3/4 turn. Experiment as bit if necessary, usually open to 1 full turn in Winter.

David A. Jabiru 3300 now CAMit 3300.

[Rick524]

Thanks David. I did as you suggested and ran the engine for ten minutes at around 800 rpm then checked the
plugs, they look good. No gas dripping from the carb or balance tube so it looks like the problem is solved.
The only thing I see is fuel in the map hose to the rdac. It slowly collects as the engine is running. I ran the
hose upward as soon as it leaves the carb map port so it will drain back to the carb, but I don't think it should
doing this.

Rick
Sonex 524

[DCASonex]

Rick,

I also frequently find some fuel in the bottom of the sense loop at bottom of the sense line (To a HACman on mine.) If depth of the loop is shallow, does not seem to have any bad effects. If any more black soot at idle, check that choke lever is FULLY closed. Hope you are in the air soon.

David

[Rick524]

Thanks David, good to know some fuel is normal at the sense port. I suspect it will be drawn out
when the vacuum increases at higher throttle settings. Planning on moving the plane to the
airport tomorrow to start putting wings on for the final inspection......feel like a nervous father, lol.

Rick
Sonex 524