Fuel Nozzle Anomaly

[Karetaker]

Howdy everyone. I have been having issues with my IO-375-M1S and thought it might be a fuel problem. So I removed the fuel injector nozzles from each cylinder. (Removed and replaced one at a time.) The #2 cylinder nozzle body had some debris on the small screen area. (Could have been a bug of some sort; not sure.) I then removed the fuel restrictor, (jet) from inside the nozzle body. I noted the jet needed to be pulled free of the body, it did not slide out on it's own and was dark grey/black in color. The inside of the nozzle body was black. This all cleaned up nicely with some solvent and a long Q-tip. The nozzle body and jet were now shinny and looked new.

The other three injector bodies and jets were just fine; shinny and clean.

What would cause such an anomaly?

I am assuming the black is oil/combustion by products, but I don't understand how that is possible. Unless the fuel pressure stopped and the compression stroke forced contaminants into the nozzle. Would the debris on the screen play a roll?

Is the injector the issue or is it a sign of some other engine problem. (Fuel delivery?)

I could relocate that nozzle and see what happens. (Every nozzle and jet assembly are identical.)

Anyhoo, I am looking for some ideas or a solution to understand and fix the issue.

Much obliged.

 

[eavila1]

Good question Mike. I just removed and cleaned mine to get ready for first engine start. mine looked shiny as well and now I almost wish I didn't touch them and hope I didn't introduce any new small particle or debri. I'll find out soon.

My guess is that at one point there may have been some sort of blockage and eventually caused the discolorization ? just a guess

Maybe someone like Mahalon will shed the light

 

[BoydBirchler]

Most likely the oil was sucked past the intake valve guide, from the rocker box, while idling.