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I’m still struggling with rough running on my 3300 Jabiru. I’ve ruled out anything mag related since it runs rough on either mag. I've checked the AeroInjector Carb, air filter, fuel filter, vacuum leaks. I’m now focused on a possible bad hydraulic lifter. I’ve done the check for a collapsed lifter and am not sure what I’m seeing. I can push the rocker in at the push rod end a fair amount with valve fully closed, but against some light spring pressure. This occurred for several valves both intake and exhaust. Not sure that this is the “looseness” referred to in the maintenance manual. A few were rock solid with valve closed, i.e. no play. I am still not convinced I have a lifter problem, not knowing how a hydraulic lifter works. The engine is a 3300 serial # 33A 2125. Any thoughts?

Things that have caused a rough runner Jab3300 for me in the past - regardless of which mag I was on, and some I can think of that I haven't experienced yet...:
1) carb spigot developed a split in it after 200 hours (happened)
2) gapped ALL of the spark plugs incorrectly (embarrassing metric/english conversion mistake - yes, I admit I did this...)
3) restriction in my fuel line - caused by the original FloScan fuel flow transducer that has a super small orifice
4) fuel vaporization on heat soaked engine - combination of the FloScan and no fuel pump due to AeroCarb installation was the root cause.
5) both spark plug rotors could be worn/end of life
6) both mag coil wires not fully seated (I've had one fall of in flight)
7) both coil caps cracked
8) stuck valve (either intake or exhaust)
9) bad lifter
10) Intermittent grounding of the mag switch
11) AeroCarb needle moving due to the jam nut not securing it in place (my neighbor had this happen on his Jab3300)
12) Flywheel magnet failing
13) Motor mount cracked/broken (engine runs fine - just feels "rough" due to extra vibration)
14) Motor mount bolt broken (same as above)
I realize that some of these are somewhat out there and there are probably quite a few others I couldn't think of. Let us know what you find out!!
Lorin

Might add one more. If you had any of the plug wires off the plugs or off the caps, before it started running rough, two wires swapped could cause this. It is easy to miss interoperate the photos in the manual, check carefully.

David A.

Thanks. A lot of good ideas there. I'll keep you posted.

Last thing I did was to inspect/clean the distributor caps and rotors. For some reason that seemed to do it. I didn't really notice much contamination or signs of arching. Still not sure why it caused roughness on both mags at the same time. It's running fine now.

An intake leak will also cause rough running