Next Steps to Troubleshooting

[drone_pilot]

Engine: Lycoming IO-360-A1A
Propellor: Catto fixed pitch 3 blade cruise prop

History: Engine was purchased used 65 hours SMOH with a light prop strike. Had an AI tear down engine, perform all AD's regarding the prop strike. Sent in crank, where it was ground and replaced main bearings. Injection system on engine is original RSA system.

Performed first engine start last week. Started right up but was blowing black smoke on right side but generally ran okay. After 5-10 minutes, started getting roughness and sluggishness at lower RPMs. Found a fowled plug and cleaned up. Ran again and fouled another plug on another Both plugs were lower plugs. Mechanic friend adjusted full lean on the fuel servo mixture adjustment but it still runs rich and very rough/unstable at low RPM. Pulled plugs and all had black soot (or however you spell it) on them. Mechanic noticed that two injector nozzles were a different part number so I purchased new nozzles for all cylinders from Aircraft Specialties in OK. The engine ran a little smoother at 1000 RPM or so but very rich and smoking at low RPMs (800RPM and less). Running on each Mag yields the same RPM and a little rough (due to the enrichened mixture). I think the mechanic may be to the end of his knowledge of how to deal with this. Also, I want to learn this thing.

What would be some good next steps to figure out why this thing is running so rich? My field sits at 3600' MSL and when you factor in density altitude lately, 4600' is the average.


I would never takeoff with the way it is running now because I feel that I'd lose the engine when throttling back. Also, I feel that it should be running smoother. It's not extreme rough but noticeable and could/should be better.

[Walt]

Assuming fuel pressure is not off the chart, I would recommend sending the servo, distribution manifold, lines and injectors to someone like Don at Airflow Performance (or other certified FI repair shop) and have the entire system tested/flowed for your engine.

[rleffler]

I agree with Walt, but also wanted to add that the reason that some of the injector restrictors were different was that they were balanced to yield the same fuel flow at peak EGT. I have three different sizes to balance fuel flow with my IO-540. Just a thought......

[lr172]

Fuel flow below 1200 is controlled by the idle mixture, not the restrictors. If you get black smoke at idle, the fix is in the idle mixture, not the injectors.

Read the Precision manual for your fuel servo. It's on web, but I can send you a link if you can't find it. You will find that maximum travel on the idle mixture mechanism is not the ultimate maximum or minimum available. You can pull off the setting device and re-clock the two threaded rods from the adjustment wheel (they have different thread pitches). This is documented in the manual and they even give you different initial setting points for different models. I had to adjust mine in order to achieve a mixture setting that wasn't too rich, yet still within the thread travel available.

If only one side is rich and the other normal, it is possibly you have a problem with your flow divider. However, it is far less probable then the mixture adjustment. I would start with addressing the mixture setting first.

Larry