#5 & #6 not firing on 3300 Jab with new Aeroinjetor

[fastj22]

Sounds like you are too lean at idle. When you go full throttle, the needle pulls out enough to give it sufficient fuel for the back two. Back out the needle in ¼ turn increments until you get them to fire with your mixture full rich. Once that is achieved, then you can fine tune.

Also, the aerocarb must be installed vertically. if installed horizontally, one side will get more fuel than the other side.

[sonex1374]

Narrobb,

Here are a few more thoughts to the latest observations.

- Engine is Ser 1460. (Early hydraulic lifter that was fully converted to CAMIit solid-lifter when at 70 hrs).

That SN probably has the airfoiled flow divider inside the intake manifold. The airfoil insert was later replaced with a round rod that caused some beneficial flow turbulence and made for a more uniform mixture distribution. That might go on your list of things to modify down the road.

- Plugs changed 30 hours ago, plugs color are text-book perfect.

Plugs should be "text-book perfect" when the engine is running perfectly at WOT. The fact that your engine is not there yet makes me skeptical that this is actually a good sign. I would expect anyone's plugs to look somewhat black and sooty from running the engine on the ground. If you were running so rich that you killed the engine at idle they would likely be excessively sooty to the point of misfiring. The fact that you didn't find sooty plugs makes me think over-rich is not the problem.

- Don't think the engine is too lean at idle if its running better at WOT and not quitting. I really did not spend much time on WOT due to the fact the engine is shaking really bad with 4 cylinders firing only. On idle, while shaking, EGT on running cylinders is pretty normal (900's, and 1200-1300's on WOT).

You must tune the AeroInjector at WOT. Anything less than WOT is just wasting your time and misleading you. Your EGT values appear OK, but this is just one element of the total picture, and not a definitive test.

- Engine mechanical pump not eliminated but a Holly 1-4 PSI regulator is after the pump; going to look into this further. Will probably rig a gravity feed bottle to feed the aeroinjector with fuel to check and eliminate issues with the regulator.

You aren't the first to attempt to use a pressure regulator before the carb, but you might be the first to use it successfully. These things just never seem to work the way we'd like them to. On the other hand, hundreds of Sonex are flying gravity feed, and they are working. It's a known formula for success. In any case, you'll need a flow test of the system, as installed, before you fly (ideally before you even start tuning just to rule out any issues before you get started).

- Distributors/Rotors; may bite the bullet and spend the $200!!! on getting these replaced.

Unlikely to be the problem. I think you've ruled these out for the time being.

While talking about these; why not having both rotors exactly parallel have no impact on the timing?

The plug fires when the flywheel magnet passes the magnetron coil and creates the spark. The cap and rotor only parse the spark to the correct cylinder. The alignment only has to be good enough to ensure the rotor is making contact with the proper cap lead when the spark is generated. Making contact a few degrees early and holding it a few degrees after makes no difference to the spark itself.

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I still think your tuning is too lean. I suggest focusing your efforts there until the WOT mixture is good, as described in the manual (100 deg EGT rise at WOT when leaning the knob). I look for WOT EGT's in the 1150-1280 range that show some slight increase when leaned, as well as a slight rpm increase (say 20-50 rpm) - this way you know you're rich enough to sustain the engine at WOT. You want to initially be a bit on the rich ride, then after the first few flights you'll gradually lean the needle setting (1/16 - 1/8 turn at a time) to sneak up on the perfect setting.

Jeff

[NARROBB]

Thanks all.

On the last test (last post), the needle is pulled all the way back, the set screw is flush with the top of the slide so don't think I can back it up further, so this is over-rich now. I understand that its going to be pain to tune this thing, but I need to get all the cylinders firing at least to start the proper tuning. Is #3 needle the right one to start with for Jab 3300?

Have to eliminate all other factors before tuning (such as Plugs, Distributors/Rotors/Wiring, use gravity feed test bottle or make sure the regulator does not output more than 1-2 PSI of pressure.

Going to test a gravity feed bottle hanging above the carb to see the effect. If the mechanical pump & regulator combination won't work at all; is going be a major issue with low wing, and a lot of changes already done to FWF including a custom CNC bellcrank mechanism for the carb for the push-pull panel mounted throttle knob.

[builderflyer]

All great ideas. Thanks.

Here are some more info and observations;

- Engine mechanical pump not eliminated but a Holly 1-4 PSI regulator is after the pump; going to look into this further. Will probably rig a gravity feed bottle to feed the aeroinjector with fuel to check and eliminate issues with the regulator.

Narrobb, having the engine pump and regulator in the fuel system is an alarm bell ringing. Thanks for mentioning that you have those items. The Aeroinjector requires very little fuel pressure and, as such, having that stuff in the system creates a potential for fuel delivery problems that the rest of us don't experience. So at this point what I would do is to make up a short length of fuel line that you can run directly from the firewall to the carb leaving everything else out of the system.

Then set up the Aeroinjector per the manual (with the flat side of the needle facing the engine) for an initial test run. I'm betting you'll be pleasantly surprised as to how your engine now runs.

If you try the above, let us know how it goes,

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

[builderflyer]

Narrobb, you're making this way too difficult.........my last thoughts.........

1. Get rid of the pump and regulator. You do have the standard fuel tank located beneath the glareshield, don't you?
2. Many have had success with a #3 needle, including myself. However, my engine has always preferred the #2.5 needle for smoother running throughout its entire rpm range, and
3. For an initial test run, set the needle per the manual . Follow the manual directions thereafter. Having a #3 needle set at the top of the slide should be way too rich to be useful for an initial test run.

Good luck,

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