Running too Rich

[Ronald Cecchi]

Hello all,

I have a 260c Turbo and it is giving me some fits that I cannot get resolved.

I have owned the plane for a little over a year, and since I have owned it it tends to run rich. If you use full rich for takeoff it can tend to bog down and not develop full power. Discussions with the prior owner and he indicated he would takeoff less than full rich to maximize performance (my home base is 2137 elev.). The mixture was set to specs as far as rpm increase when you leaned to shut the plane down.

I have worked with my a/p to address the richness issue because of the discrepancy in how you operate versus the handbook and evaluated several issues. The fuel servo was not replaced during an engine overhaul prior to my ownership and was considered to be the problem. That was replaced during the last annual but that did not change the performance.

Now we have gone through my first winter and brutal weather in the Northeast combined with work/personal issues, I did not fly the plane for over close to 4 months. The mixture problem seems to be getting worse. I have had problems failing to keep running at idle. If I lean out it runs fine, but need lean more than half way back to keep it idling smoothly.

The problem is worse with the electric fuel pump on and that makes it struggle more. I have had other people with more experience that I fly the plane and they agreed there was a mixture problem and thought the fuel pump exaggerated the problem. The manufacture threw out the possibility of a bad check valve in the electric fuel pump. My logic would indicate that this would be a problem when the pump is on but not explain the richness problem when the pump is off.

Basically I am looking for input on the richness problem and/or the fuel pump check valve theory to see if others with more knowledge or ideas than myself can give me some ideas how to progress with this. The weather is finally improving and I am frustrated that my plane won't let me enjoy it like I want to.

Thanks for any input on this.

Ron

[Kristin Winter]

Do you have an engine monitor installed, and if so, are the EGT's normal?

[Ronald Cecchi]

I do not have engine monitor installed. Next on my list to add. And I have only been test flying the plane short distances since this issue land leaning by historic fuel flow values and not leaning for peak egt.

[Kristin Winter]

It might be worth flow checking the injector lines and nozzles. If one is partially clogs, it can cause the others to run rich.

[Clarence Beintema]

Does your engine have one piece or two piece fuel injection nozzles? If two piece it is possible that one or more of the inner parts of the nozzle is missing.

Does the engine have a diaphragm pump or a Lear Romec pump? The pressure on the Lear is adjustable and may be set too high. Values are in the Lycoming direct drive overhaul manual.

Clarence