Engine runaway is a common issue, even with LA46s, a comparatively even tempered CL off the shelf engine. Getting these engines to run right is also complicated by the scatter shot advice you're likely to get at the field (or on the forum.) All of the above ideas no doubt have worked in a given situation. Problem is there can be many different causes or combination of causes that make an engine to go berserk, what worked in one situation may not work in another. An unsystematic approach can add to your frustration. In my experience a systematic approach, making incremental changes, works best. I would approach a new engine as follows. First would be initial setup. I would do a baseline engine configuration, one that has worked for me and other club members.
Baseline: if the engine uses a remote needles, swap it out for an OS FP needlevalve available from Tower or elsewhere. The FP25-40 part will fit through the venturi, match up perfectly. At times, in our experience, the needle out on a stalk can exaggerate vibrations issues, especially true for profiles. Use a second head gasket. This usually makes the engine milder and easier to tune. Our club has found two glow plugs that match up well with this engine. Thunderbolt RC long and an Enya no. 3. We've had good luck with the 111/2X4 apc. If you can get Powermaster fuel, try 22% (50/50) 5%. Fuel quality varies enormously. All oil, methanol, nitro is not equal. Also, fuel needs to be mixed accurately by volume. Even slight deviations in proportion of ingredients can be an issue. Two shots of original Armoral to the gallon. We have found the Tettra tank problematic. Symptoms include an issue like the one you describe. Not sure why. Could be the bladder doesn't collapse fully enough or easily enough (thickness of material?) causing a slight vacuum as the fuel runs out, aggravating a lean setting. Others have made the Tettras work. In any case, Tettras are a non-uniflo tank, like all non-uniflo tanks it's likely to experience a gradual leaning of the engine during a flight. A function of the reduction in fuel head pressure. Uniflo tanks (when they work) make for a steadier setting throughout the flight. I'd use a different tank, at least initially. Either a clunk tank or an RSM profile uniflo (the long one inch thick tanks). If you know someone who can configure a clunk for uniflo try that. Pressure test everything. Testing the new tank(s), underwater. Even a slight trail of bubbles is trouble. Tanks must be tight. Check your filter (use a filter that you can open up) a slight bit of dirt or gook can cause a big problem. I'd initially run muffler pressure to the uniflo. If any weirdness happens, I'd disconnect the uniflo, run muffler pressure to the overflow and cap the uniflo. I use muffler pressure in order to provide consistent pressure to the tank. In my experience vents open to airflow can vary pressure too much. Causing the engine to run differently upwind and downwind.
Profiles are subject to weird vibes more often than full bodied planes. This no doubt complicates your engine setup.
The above configuration is where I start.
I would then ear set the engine (not using a tac), I am looking for a setting that is on the rich side. Important. It's best to creep up on an accurate setting click by click, very gradually getting leaner. Fly. Listen to the engine. The flight setting is what counts (obviously). Often (most of the time?) ground setting and flying setting differs. This is a key issue and a common problem. Adjust one click or two clicks at a time. This adjustment is often very sensitive. One or two clicks too lean can cause a runaway. If the engine runs away, two clicks rich. See what happens. It's not uncommon for a plane, especially a profile, to run either too rich (or lean) but unload (or get out of a weird vibration harmonic) in the air and run great. When you find a setting that works well, leave the engine at the setting, at the end of the flying session. Use it, next time out. Weather condition, temperature, barometric pressure, can effect settings. Again. Make adjustments increment by increment, click by click. After a while you'll probably hear when the setting is right on the ground. Some plane/engine combos like to barely break lean on the ground, some like a more constant back and forth, etc. I even had a profile that took off in a dead lean 2 stroke but unloaded (got out of a bad vibe?) in the air and went into a very useful consistent break during the flight.
Topic: What would cause this? (Read 2264 times)