SonexBuilders.net

Evening all:

I've been discussing these problems with Mike Farley recently...let me give a quick synopsis:

Last flight I took in mid-February was pretty uneventful, however I noticed that the engine was developing a "roughness" at cruise speed and the throttle was balking a bit after landing. I had about 46 hours on the engine at this point, and had done a valve adjustment just before 40 hours. Feeling like maybe I had the mixture set a bit too rich during the winter, and possibly fouled the plugs, I decided it was a good time to check these, change the oil, and prepare the airframe and engine for spring. Here are the items I did (in succession):
1. Changed oil (did not remove or clean oil screen).
2. Removed all 8 spark plugs, and judging condition ordered new ones (same brand and type as recommended - Autolite 4163).


3. Gapped and installed 8 new spark plugs.
4. Cleaned and oiled K&N air filter
5. Adjusted mixture 1/2 turn lean (had adjusted it 1/2 rich in late November).

When I went to restart the engine...it didn't want to start. Once I overcame that problem (had to open the throttle more)...it didn't want to keep running. After many cycles of starting, briefly running, stumbling and dying, I was able to coax the engine to run...somewhat.

I checked the obvious items like spark plug wires mixed up. That wasn't the problem. I was getting fuel. So maybe the "clean/oiled filter" was choking the intake? Removed the filter and ran it another day, to take these videos.

1st video is of a full static power run, you can see it reacted okay to this test, until I powered back below 1500 RPM and the engine quits
https://youtu.be/WRqejJy7esM

2nd video is a mag/coil check, it's showing a much larger RPM drop then usual. I've not touched the secondary ignition trigger timing:
https://youtu.be/ExlxHtATG6E

Thinking maybe some of the new spark plugs were bad, I cleaned the original ones, and reinstalled them (that didn't help). Mike was thinking maybe the mixture was too lean, so I reset the mixture back to my "winter" setting even though OAT's are back in the 50's to 70's. That didn't help so I richened it up again today another 1/4 - 3/8 turn. No joy.

Another item to note. In December I began to notice a increased fuel leak at the finger strainer and shut off valve. The teflon paste is breaking down from exposure to 100LL. I have not refueled since early February and had about 6-7 Gallons of 100LL remaining on board after sitting for 4-5 weeks. I have never used anything but 100LL with this engine.

Beginning to wonder if I have contaminated fuel? Or water in the tank (although sample was clean and clear blue). Or crud has passed through the strainer, gascolator and clogged,the fuel passage inside the AeroInjector?

At a loss. Engine is completely stock setup. Has run very reliably since I got it dialed in last year, and completed Phase 1 testing with no hiccups at all, until now.

Also checked the other key items (intake hoses are tight and no air leaks), all ignition wires are in good condition and properly connected, throttle plate is opening and closing correctly and mixture control is still set up per manual.

My next step is to drain the tank, take apart the fuel line fittings, shut off valve, and clean everything including the AeroInjector and reseal the fittings with EZ Fuel Lube (got this from Aircraft Spruce recently).

What am I missing?

I had very similar issues and it was driving me nuts. I tried all kinds of things with no luck. Finally I decided to test the plugs. I found 5 of the 8 were not in spec. I then tested a few of the old ones I replaced. More were bad. I bought 8 more new ones, ohmed them and some of them were out of spec new from the box. Returned them and bought 8 new NGK plugs and installed them. Poof, like magic it started and ran like it should.

Not sure what the deal was with the autolite plugs but switching to the NGKs was what solved the issue for me. Some of the autolites were from the aerovee kit, some were sourced online, some were from local auto parts stores, all had bad ones in the sets...

Is the NGK DR8ES-L equivalent to the AutoLite 4163?

I would go tripple check the intake boots. Actually remove them and look for cracks. You may not notice them until the engine flexes in the mount. One other off the wall idea is to check the secondary ignition magnet. It's a long shot but I had one come loose from the holder early on in my flight testing. The primary ignition only works after the engine is spinning a few hundred rpm. Rough running at idle and hard starting would lead me to look closee at the secondary. It isn't unheard of for the secondary coils to go bad either.

Keith#554

Is the NGK DR8ES-L equivalent to the AutoLite 4163?

I know they are the DR8ES I use, I don't remember if they were the -L or not. I can look this afternoon when I get out to the hangar.

I've noticed a very similar problem due to issues with re-installing the screw on the Aeroinjector needle. Sometimes it doesn't instantly lock the needle carrier in position and the needle ends up getting twisted an extra turn or two lean before everything locks solid. It's a little bit of a hassle, but now I always remove the air filter, mark the needle with a sharpie, and watch the mark while I lock it in position. Honestly, it always rotates a little bit when I install the set-screw so I think less about "number of turns" and more about how far I'm moving the sharpie mark.

Fastcapy, do you remember how far out-of-spec your spark plug resistance was? I wouldn't really expect the resistance to be that critical, so your experience is pretty interesting.

Scott,

I second what Gammaxy suggests with the tuning of the AeroInjector. That needle can move very easily when you tighten the set screw. That has confounded countless builders, myself included more than once. Sonex has a technique they recommend for helping to prevent the needle from moving when tightening the set screw. I would contact them to get the details on that.

Unless you put excessive amounts of Teflon paste on the threads, it is unlikely that would cause any problems. It is not a bad idea to check the finger strainer at some set intervals (perhaps at annual) in case some leftover shavings during construction find there way down there. It is also a good idea to check the fuel filter at annual or every so many hours.

I understand you can clean the AeroInjector with mineral spirits and or compressed air without removing it from the plane. You would have to remove the fuel line and the mixture arm and blow out the ports.

My bet is that it is the mixture needle moving when you try to adjust the mixture and then tighten the set screw.

Remember OCSAMS razor. Start with the most obvious problem first. Do one thing at a time and test and then move on to the next one. Eventually you will come up with the solution and by doing it sequentially you will know what caused the issue and thus learn along the way.

Please keep us posted on your findings.

Thanks,

Jake

Jake and Chris,

Thanks for your thoughts and replies. Yes it's important to limit the changes to one item at a time! Retest engine between each process. When I first started on the "simple maintenance" I never expected this to snowball...

New spark plugs (NGK) were ordered just to try them out!

gammaxy wrote:I've noticed a very similar problem due to issues with re-installing the screw on the Aeroinjector needle. Sometimes it doesn't instantly lock the needle carrier in position and the needle ends up getting twisted an extra turn or two lean before everything locks solid. It's a little bit of a hassle, but now I always remove the air filter, mark the needle with a sharpie, and watch the mark while I lock it in position.

Besides marking with a Sharpie I also put my finger up inside and hold the needle in place with my finger so it doesn't rotate. Has worked 100% for me.

Have you checked the amount of play in the ball joint of the needle holder? Mine had about .025 inches which amounts to almost a half turn of the screw. With this much play the needle can be "sucked" leaner from the setting you adjust to. Tighten it up buy pinching or shimming to eliminate the play and still be free to rotate. This is a bigger problem than movement by the locking screw. Hold the needle with your finger if you think it's moving and run the engine without the air filter to eliminate that variable.