40 FP NEEDLE VALVE ASSEMBLY?
06-25-2004, 08:30 AM
#1
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40 FP NEEDLE VALVE ASSEMBLY?
I was wondering if any other needle valve assembly with an O-RING would fit into this engines carb?(no o-ring with this one)
Also,how do you know when either the piston or sleeve is worn out?(engine starts right up,idles good,looses power at full throttle)
Im trying to pin down this problem im having with this engine.
Thanks for reading!
I have to add another observation I just found,when I hold the prop at the compression it seems to bleed off.
I tried it with my other engines Magnum 46 and an MDS 58 and both hold compression when prop is held.
Just another thought.
Also,how do you know when either the piston or sleeve is worn out?(engine starts right up,idles good,looses power at full throttle)
Im trying to pin down this problem im having with this engine.
Thanks for reading!
I have to add another observation I just found,when I hold the prop at the compression it seems to bleed off.
I tried it with my other engines Magnum 46 and an MDS 58 and both hold compression when prop is held.
Just another thought.
06-25-2004, 09:39 AM
#2
My Feedback: (11)
RE: 40 FP NEEDLE VALVE ASSEMBLY?
If your high-speed needle's not too lean, and the engine won't hold a needle setting at full throttle, it's possible that something's wrong with the piston/liner fit. If the engine's been run a lot, had a lean run at some time, or had foreign object damage (dirt), then when the engine warms up, the piston/liner fit becomes too loose and you lose compression. This would cause the power sag.
It's also possible that something in the fuel system's causing the mixture to become slightly lean. This would cause the engine to gradually overheat and sag in RPM. Vibration can agitate air into the fuel and cause the mixture to go lean. If that's the case, it may not happen on the ground because you change the vibration mode when you hold the airplane...your hands absorb some of the vibration, as do the wheels on the ground. When the model gets into the air, it can vibrate freely, and the fuel can be agitated.
It's not likely to be a needle valve, especially if you can get a good adjustment initially. The only thing that would cause damage to the o-ring on the needle would be careless removal and replacement, use of a petroleum product that got onto the o-ring, or some other kind of mis-handling.
It will take some detective work to find the problem. Put the engine on a test stand and carefully run it. If the engine runs fine as long as you want it to on the test stand, then the problem is in the system of airplane/engine/mount/fuel system.
It's also possible that something in the fuel system's causing the mixture to become slightly lean. This would cause the engine to gradually overheat and sag in RPM. Vibration can agitate air into the fuel and cause the mixture to go lean. If that's the case, it may not happen on the ground because you change the vibration mode when you hold the airplane...your hands absorb some of the vibration, as do the wheels on the ground. When the model gets into the air, it can vibrate freely, and the fuel can be agitated.
It's not likely to be a needle valve, especially if you can get a good adjustment initially. The only thing that would cause damage to the o-ring on the needle would be careless removal and replacement, use of a petroleum product that got onto the o-ring, or some other kind of mis-handling.
It will take some detective work to find the problem. Put the engine on a test stand and carefully run it. If the engine runs fine as long as you want it to on the test stand, then the problem is in the system of airplane/engine/mount/fuel system.
