Starting Procedure Help, talk me off the ledge

[BenCharvet]

I've been playing with my new to me Sonex since last May. Its a tri-gear legacy with a Jabiru 3300 and AeroCarb. I've solved the vapor lock problems I was suffering during the hotter months of summer and have about 30 hours on it so far (170 tt engine and airframe). After it starts its running well and it's fun. The problem is it only seems to start about half the time, especially since it cooled down here some. I had a post last month where I documented a repair I did to one of my starter bushings, and the starter is turning over fine now. Because I've had issues with loading the engine up (fuel dripping from cowl), I've started pushing the mixture in as I start to crank. This morning was a beautiful day, no wind, 34 degrees overnight, but up to 55-60 by 10:00AM. Because it was so cold overnight I pulled the engine through about 6 blades prior to start, it cranked real slow initially, but loosened up and was cranking at the normal speed. I continued to try with 4 or 5 cranking cycles with the fuel on and mixture in with no fire. I'd turn off the fuel, open the throttle and crank a bit to clear it in case it was flooded again. Twice I let it sit for 5-10 minutes just to let everything cool down. Eventually the EarthX battery was obviously starting to give up and I pushed it back in the hangar.

I'm really about ready to throw in the towel, but thought I'd ask you folks for advice on how your starting procedure goes, and if you intermittently have similar problems. At this point, after it starts its fine, but I can't plan any cross countries with my friends, and I'm afraid of getting stuck somewhere if I ever took it on an overnight. (It restarts fine if I stop somewhere for fuel)

Ben Charvet
Sonex Legacy 809SX

[wlarson861]

First thing I would do is check the oil temperature (I use a multi-meter) if the oil temp is below 45 degrees I preheat until the oil is at least 45F.

[sonex892.]

Hey Ben. Have you checked the coil to magnet gap. An incorrect gap setting at the coils will make a cold Jabiru hard to start. I find the gaps easier to set using 2 feeler gauges per coil. Otherwise the magnet tries to pull the coil down making things difficult.
Steve
Sonex 892

[NWade]

Have you checked the mixture control on the Aerocarb itself? I (and others) have found that when the mixture knob is pulled to the “full lean” position it might still allow fuel to drip through into the intake. So you might be unknowingly flooding the thing. I haven’t flown my bird yet, but have done extensive short ground runs (while troubleshooting a boost / MAP problem with my Aerovee Turbo), I found it best to keep the fuel shutoff closed, set the throttle and switches to their proper position, then open the fuel shutoff valve, count to two, and crank the engine while pushing the mixture smoothly from idle cut-off to full-rich.

Hope this helps! If nothing else, remember that you need fuel, a spark, and intake air. Verify that you’re getting each one of these in order to find the root of the problem.

—Noel
Sonex #1339

[DCASonex]

If you have not already done so, switch to the Iridium plugs, Their smaller sharper points will fire at lower voltage and thus lower RPMs. They also last MUCH longer.

David A.

[sonex1374]

Ben,

I have found the key to getting started in cold weather is to stack the deck in your favor. Ensure the battery is topped off and ready to spin the engine with gusto. Proper weight of oil. Preheat until the engine sump, intake and cylinders are warmed so the fuel will vaporize and the engine isn't so tight from the cold-soak. And lastly, don't flood the engine by failing to start on the first try.

Last winter my battery was showing it's age and was not turning the engine over as quickly as it should have. It started fine at temps above 50 deg F, but colder it was just not getting the engine spinning fast enough. Simply observing the starting RPM it didn't seem all that slow to my observation, but at the cranking speeds the Jabiru uses it doesn't take much of a slow-down to affect it. I replaced the battery with a new Odyssey P625 and the problem went away immediately. The take-away is that even though the battery would crank the engine and worked some of the time, the nuances of a slightly weak battery were not obvious but made a big difference in outcome.

I suggest trying some pre-heat on your engine (getting the fuel to vaporize in the intake is key). While the pre-heater is on you can also plug in your battery charger to top-off and warm the battery to get it ready to crank. If these solve the problem then this might be the needed technique for cold starts. If this still doesn't work reliably, then maybe it's time to take a second look at cranking RPM and see if perhaps it's too low to be effective. This will be difficult using your perception only, so you'll need to figure out how to quantify your observations to make sense of it. You might need to have someone measure the prop RPM with a handheld model airplane optical tachometer, or measure the actual battery voltage sag (at the battery terminals with a meter) while cranking.

The last item to consider is the total capacity of the EarthX battery. The battery voltage is higher than an Odyssey, and it typically cranks enthusiastically. However, total capacity of the battery is far lower than an Odyssey, and that translates into less start attempts before exhaustion. Also consider that if you deplete the battery down to say 40% capacity getting the engine started, that battery is going to demand a high charge-rate from the alternator, and that will stress the entire charging system (pm coils, voltage regulator, and any joints or terminals in the wiring that are not in perfect condition). You wouldn't be the first person to barely get the engine started, thank their lucky stars that it all worked out, only to find out later the battery's charge-demand overheated and destroyed something else in it's attempt to recharge itself quickly. There's probably a way to mitigate this (maybe periodically turning off the alternator for a few minutes every so often under high demand so it can cool down), but you'll have to experiment with that because I'm not sure exactly what might work best.

Jeff

[builderflyer]

Ben, you'll get a "million" opinions on this but what has worked for me over the years under similar temperature conditions is this:
1. A mixture needle setting that has worked well during the warmer months won't necessarily provide enough fuel for a cold weather start. If this is the case, you can crank the engine for days and it'll never fire. We don't have a manual choke to use so the first and only thing to do is to adjust the mixture needle slightly more rich.......maybe a half turn counterclockwise. Don't worry about WOT as you've got a mixture control to take care of that.
2. Warm the air inside the cowling around the Aerocarb. I use a heat gun carefully aimed through the outlets for about 5 or 10 minutes. This step may not be necessary if the airplane can sit out in the sunshine for a while before attempting a start.
3. Before cranking the engine, don't ever push the mixture control to full rich for more than a few seconds. If the engine doesn't start immediately, don't leave the mixture in the full rich position when not cranking. For a hot start, don't push the mixture in at all until the engine is already being cranked. Once the engine is running at idle, remember to do extensive leaning, regardless of the OAT.
4. If the engine doesn't fire quickly after doing the above, it's probably not going to start at all so try not to run your battery down in futile attempts. Go back to Step 1 above, the beginning, and try again.

A really important thing to remember is that if the fuel tank valve is open and the mixture control is other than at idle cutoff, there is fuel running into the Aerocarb. This is unlike any other conventional carburetor you may have flown behind and if you don't take it into account, you may never get the engine started.

Finally, always pay attention to what Jeff says..............

Good success,

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

[GraemeSmith]

What Jeff says.

My battery is "tended" by a solar cell on top of my tie down box and always fully charged. Then get it all nice and warm.

A Red Dragon unit. The hose is just flexible dryer vent pipe with an insulated/fiberglass cover (sold for AC duct) over it. Propane for fuel and 12v from the truck for the fan. The blanket is heavily padded. I heat gently from underneath and when the front cylinders are slightly warm to the touch - it starts like a summer day. You just need to be richer on the carb for the low DA.

[N111YX]

One trick here is to get a piece of brass sheet 10/1000th's of an inch thick, cut about a 1/2 by 6 inch piece, insert between the coil and flywheel, let the magnet grab it and set the gap, tighten the screws then pull the brass strip. Easier than feelers.

Hey Ben. Have you checked the coil to magnet gap. An incorrect gap setting at the coils will make a cold Jabiru hard to start. I find the gaps easier to set using 2 feeler gauges per coil. Otherwise the magnet tries to pull the coil down making things difficult.
Steve
Sonex 892

[builderflyer]

One trick here is to get a piece of brass sheet 10/1000th's of an inch thick, cut about a 1/2 by 6 inch piece, insert between the coil and flywheel, let the magnet grab it and set the gap, tighten the screws then pull the brass strip. Easier than feelers.

I don't recall what year or serial number it was but the the magnets on the early engines were not all exactly equidistant from the center of rotation. So those of us having one of those engines have to first determine which set of magnets is closest after which it's necessary to rotate those magnets past the ignition coil being checked for clearance taking multiple measurements with a feeler gage. It's a real time consuming pain. I only wish the abovementioned good suggestion worked for all.

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