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Hello! While on a multi day journey a friend and I encountered some engine problems which after multiple days and a couple consultations with A and Ps we still have not resolved.

The problems started as we turned off the electronic ignition after landing. Ran rough on the mag, almost like it wasnt firing on one cylinder. Troubleshooted cleaning the spark plug boots and also resealed one of the intake manifolds with red rtv (the seal had been a recent problem with the other intake manifold). Starting up the next day, the engine ran well on both ignitions and we continued on our journey.

1.5 hours into a following flight we got an occasional stutter of the engine. Like fuel flow was interrupted for a split second. As we continued on, the problem got worse as the stutters occurred more frequently. When this happened we diverted to troubleshoot the problems.

Doing run ups on the ground, resulted in the following problems: engine still ran rough on the mag and fine on the electronic ignition. Engine would run fine at idle, at 1400rpm the engine would run very rough and die if kept there. Past 1400 rpm the engine would run fine, and then die again when advancing to 2400rpm. This occurred either on the electronic ignition or the mag.

We checked that the plugs were clean and that the gaps were correct. We also tuned the aeroinjector and cleaned it with carb cleaner. Tuning the aeroinjector mitigated the engine dying at 1400 and 2400 rpm. While tuning, the engine died at 1800 (and ran fine at all other power setting.) And after more tuning wouldnt die at any power setting.

At our final setting, the carb is now quite rich at idle, and we were not able to get a rise in EGT while leaning at full power. Potentially indicating that the carb is also lean at full power. Still it runs smooth with about 3050 rpm static on the ground. All temps/pressures within limits. We’re using a #2 needle.

We had a couple A&P’s look at the mag issue, they insulated the spark plug leads and checked for grounding problems. Ultimately they were able to fix the issue of the mag running rough. I departed and after 5 minutes of flying I once again encountered the occasional quick stutter of the engine. After a couple minutes this once again became more frequent and I came back in for landing.

Next plan is to start looking at the fuel system, the stutters have all been on the same tank of gas (maybe fuel contamination?) and have yet to check the filter screen in the gascolator.

Any ideas on what could cause the engine to behave in flight in this way? I’m starting to run out of troubleshooting options with the plane hundreds of miles from home :(
Any insight would be greatly appreciated.

Thanks you!

Ethan McIntosh
Sonex 888

When running poorly what are the EGT's doing? Are all cylinders matching or do you have one or two cold EGT's?

I have 2 EGTs for the rear cylinders which both match (around 1240 at full power full rich). Right now the engine runs smooth at full power on either ignition but occasionally stops for a split second before resuming smooth full power operation. This starts happening every couple minutes and then increases in frequency as the flight continues.

Can you confirm the issue happens either on mags only, electronic ignition only, or both? If so then I would not suspect ignition.

If not ignition, then it's probably fuel. What is odd is that fuel delivery issues generally get better in cooler temps. I'm assuming it's cooled down in the northeast.

What is your fuel routing? What components do you have, etc? Of course the mystery is why is it bad now.

I've had my Aerovee stumble when too rich, during phase 1. Happened at full fuel as I was climbing. Higher fuel levels mean more pressure at the Aerocarb and richer mixture. So not a root cause but sounds like your adjustments have made it too rich, which is not good.

Is there any way way to monitor your carb temp? Sounds like you might be getting vapor lock. I had similar problem, worse actually, until I installed a small NACA scoop on front of the air filter.

I could be wrong but it sure sounds like the old problem. Welcome to the "Burps". Insulate your entire fuel system. Eliminate the gascolater because you can't insulate it efectively. The red fire sleeve may not be enough.
In my Onex I had to add a blast tube to the AeroInjector itself to stop surging during taxi after flying.

Ethan, do you have a gascolator and if so, what kind? Given your previous flight history, my experience is likely not related to yours even though your current symptoms are similar to what I experienced on my first and subsequent test flights. My plane was originally equipped with an ACS gascolator and the "coughing" of the engine at full power settings did not resolve until i changed to an Usher gascolator whereupon the coughing ended. And when I say coughing, I mean that the engine would literally die for a second before continuing to run. Sure gets ones attention, especially on a first test flight. And, this is a more significant event than when others speak of the "burps".

If you do have any gascolator in your fuel system, temporarily bypass it and see if the symptoms have disappeared. If they have, you found the problem.

Good luck. I hope you get it figured out soon,

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

I had pretty much the same symptoms and traced it to weak springs holding the exhaust together. Hot gasses were exiting the slip-joint and heating the Aeroinjector causing vapor lock.

In my humble opinion, the slip-joint is backward in the first place. Any escaping exhaust blows forward and rattles around the injector before making it's way out of the cowl. A welded seam is desirable if you get the chance.

The fuel system had an Usher Gascolator. About 10 flight hours ago I installed a used redcube fuel flow transducer on the cockpit side of the firewall. The transducer never worked, but presumably this was due to bad circuitry as the impeller moved freely before installation. The design allows for fuel flow to be uninterrupted with a stuck impeller.

Currently draining the fuel and will check the screen in the gascolator. Going to try new fuel and will remove the redcube from the fuel system. I can investigate how I would go about routing the fuel system past the gascolator. Will try fresh fuel as well. The outside air temperature has been in the 40s and 50s for this trip which is quite a bit cooler than the 70s and 80s when I first got the plane.

Don’t forget to check the finger strainer in the tank as well. Disconnecting the line at the carb before you pull anything else apart and doing a fuel flow test would also be a good idea. It will tell you if you have a clog or restriction somewhere.