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Engine basics => Engine set up tips => Topic started by: Chuck Feldman on December 23, 2012, 08:22:01 AM
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My La 46 has developed a run problem that remains unsolved. I have done everything I know of to find a fix. To no avail. So here is the problem. Soon after take off the engine goes lean. Everything I have done does not change it. The only thing that I have not done is to run more Castor in the fuel. Fuel lines, tank, clean muffler ports, check needle valve all have been done and repeated. This engine is high time. It has been in service since 2004. Always ran great. I took it apart just now and found only that one side of the piston is a different color that the other side. I am wondering if this sleeve and piston are worn out.
Thanks,
Chuck Feldman
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Hello Chuck,
Sounds to me like a classic air leak problem. I would try resealing the backplate with some silicone sealant. The other possibility is the O ring sealing the venturi could have become hard and is leaking. Backplate would be favourite though!
The LA piston and liners don't last as well as some other makes. I have had two wear out sofar. My problems was poor compression and difficult starting. When the liners go bad, you can usually see the brass showing through the very thin nickel plating. The P/L are cheap enough to replace if that is the problem. My limited experience is that the effect is gradual. If you have had a sudden change in the way the engine runs, then almost certainly an air leak somewhere.
Andrew.
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Chuck, profile or full body? Either way could be a vibration problem arising like loose engine or tank mount.
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Yes. The liners go. Coloration variation on different sides of the the piston on an old engine could be normal blow bye from normal wear. The crank pushes one side of the piston up against the liner, harder than the other side. The forces, side to side, are asymmetrical. It's also possible that the liner has become slightly oval, after being run for years. From what I understand the liner is thinner than the FP liners that preceded the LAs. I've seen FP liners wear through as well. Tell tail scrapes on the nickel, when the brass shines through that P/L is cooked. Right. Back plate, o ring on venturi, look into that. Bushing to crank leakage can also be problematic in worn engines. I've even heard of a needle valve that wore out (vibration?) clearance on the thread to needle opened up, didn't seal. When a new needle was put into the needle valve, run returned to normal. Might be the airframe as well. Loosening up of structure, softening of nose, can change the vibration harmonics of a given engine/airframe unit. Vibes on the ground differ from vibes in the air. Pin hole leak in the tank, not apparent unless the tank is pressure leak checked under water. Even a small barely detectable leak can cause havoc. Especially so if you are running muffler pressure.
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HB~> HB~>The tank tubes could be split, remove the back of the tank and replace all tubes . HB~> HB~>
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OK Guys Thanks for all the tips. I think I will retire this one and get the new on out of the box.