[John Lawton]

Hey Steve,

I just went through an engine seminar on the Jabiru 3300 last November. The Jabiru also uses a Bing carb, although in a single carb configuration with a larger version of what is used on the Rotax 9xx. The seminar covered the Bing diaphragm type carb and their theory of operation in depth, including do's and don'ts of cold weather starting.

Aside from the weak battery, the mistake you made was cracking the throttle. The Bing is a 3 stage carburetor. It has a starting carb, idle carb and a running carb in one package. If you crack the throttle with a Bing it shuts off the "starting carb" portion of the Bing that initially primes the fuel circuit and the engine won't start no matter what you do because it's starved for fuel in the priming circuit. Of course, this has a lot to do with where you throttle stop is set, but I'd bet that was your problem.

For cold starts, it was recommended that you keep the throttle closed against the stop and use full choke to prime the circuit until the engine catches. Then, you can bring in some throttle after the engine is running and ease the choke off as it warms up. Rotax recommends that you idle above 1800 RPM, too. Apparently, harmonics below 1800 RPM play hell on the redrive. I recall that the Rotax ignition box won't produce sufficient field to cause the plugs to spark until it reaches around 700 RPM, so a weak battery doesn't help much, either. You can try turning off one mag circuit until it catches, too. I've read this helps with cold starts on the Rotax 9xx. Preheating the engine and oil is also a good idea, as is synchronizing the carbs periodically, especially if you notice a rough idle situation on a warm engine.

FWIW, I keep my battery on charge using a "Battery Tender" trickle charger. This charger shuts off when the battery is peaked so you don't boil the electrolyte unnecessarily. I have several of these chargers and have done this for years with batteries in other airplanes, my golf cart, lawn mowers, tractors, etc. Keeping the battery topped seems to make them last longer.

Hope it helps!

Regards,

John Lawton
Whitwell, TN (TN89)
Ximango #135