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Home> Maintaining your Continental  and Lycoming engine

The best method of cleaning and inspecting the filter is to first dry the filter with air and tap on it open side down on a clean piece of paper. Inspect the contaminates that fall out for signs of fuel system deterioration. Look into the center of the filter while shining a light through the outside. You should be able to see light through the weave on most of the surface areas. If you blow through the filter there should be very little restriction. Clean with a solvent such as M.E.K. or acetone. After the screen has been cleaned, blow it out with compressed air.

Next, make sure the rigging is correct and that the throttle and mixture controls are both traveling to their full open and full closed stops. Also check to see if you get a 25 to 50 rpm rise at idle when the mixture control is moved from full rich to idle cutoff. A lean idle mixture will cause poor acceleration of the engine. To adjust the idle mixture, turn the scalloped wheel at the side of the injector either toward rich or lean as required until the desired rise in rpm is reached. When the linkage is adjusted to a longer length, a richer mixture is provided. When the linkage is shortened, a leaner mixture is provided. Each time an adjustment is changed, clear the engine by running it up to approximately 2000 rpm before making a mixture check. If the setting does not remain stable, check the idle linkage. Any looseness in this linkage causes erratic idling. Make allowance for the effect of weather conditions upon idling adjustments. The relationship of the aircraft to the direction of the prevailing wind has an effect on the propeller load and its rpm. It is advisable to make the idle setting with the aircraft crosswind.

After adjusting the idle mixture, you may have to adjust the idle rpm. A good idle rpm is 600 to 650. If you are experiencing a rough shut-down and the engine doesn't want to quit when the mixture control is retarded, it may be because there's a score on either the mixture control jet or rotating plate, or a bad "O" ring on the jet. Discon- nect the fuel line coming out of the fuel injector and leave the fitting open. Pull the mixture control and throttle all the way back (off) and turn on the boost pump. There should not be any fuel coming out of the open fitting. The mixture control assembly can be removed and the scores eliminated by lapping the mixture control jet and rotating plate on a good lap plate using a mild abrasive such as Bon-Ami. The final lapping should be done with the jet and plate together. Clean and re-assemble the parts using a new "O" ring. If the engine does not shut down smoothly but fuel is not leaking out the end fitting, then nozzles are plugged.

Normally-aspirated engines have a screen covering the air-bleed hole which makes a visual inspection impossible. Therefore, you must remove the nozzles from the engine and clean them. Hoppe's No. 9 makes a good cleaner and can be purchased at a gun shop. Soak the nozzles for 20 to 30 minutes in Hoppies and then rinse with Stoddard solvent and dry. When cleaning newer two-piece nozzles, be sure each restrictor is kept with

its respective body. On old style one piece nozzles, inspect the top threads (at the fuel line connection) for damaged threads. Damage indicates the fuel line nut has been over-torqued. This can cause a reduction in the size of the air restrictor. Standard nozzles flow 32 pounds per hour at 12 psi. Nozzle cleaning instructions are included in Lycoming Service Instruction 1414. The first indication of dirty nozzles is an increase in indicated fuel flow at various power settings. Fuel stains around a nozzle also indicate cleaning is necessary. The air-bleed hole on turbocharged engines is shrouded and vented back to the compressor discharge pressure, "deck pressure". Inspect these lines and fittings to make sure they are free of dirt, leaks, or obstructions. Remove the shroud from the nozzle and lean and blow out with compressed air. Make sure the letter "A" that is stamped on the hex portion of the nozzle is pointed down (30 degrees); this positions the air-bleed hole up. Torque the nozzle to 40 inch pounds and never over 60 inch-pounds ( 1/2 to 1 flat of the nut from finger tight position then stop). Caution over-torquing can distort the nozzle and change it's flow characteristics.

Check for an internal leak in the fuel injector center body seal. All the fuel that is delivered to the engine should go through the individual fuel lines to the nozzles and on into the combustion chamber. If there's an internal leak in the injector, fuel enters the injector at the throat and goes to the cylinders much as in a carbureted engine. This extra fuel flow does not show up on the cockpit fuel flow gauge and will cause the engine to run rich. The pilot may have to retard the mixture control on flare-out and landing to prevent the engine from stopping or the mechanic may have to adjust the idle mixture every week or two because it has drifted rich. There's a simple test you can make to check for an internal fuel leak. Remove enough of the induction system so you can see the impact tubes in the throat of the injector. Then disconnect the fuel line from the fuel injector to the flow divider and cap off the fitting in the fuel injector. Move the controls to the full throttle and full rich position and turn on the boost pump. Any fuel observed coming out of the impact tubes of the injector means the center body seal is leaking. If you have a leak, then send the injector in for overhaul.

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Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.