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Carburator Question

Old 10-12-2015, 01:54 AM
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Default Carburator Question

I purchased a Turnigy 32 which has a Tillotson carburetor on it. I ran two tanks through it yesterday with 32:1 Yamalube mixed into 97 octane. The engine fired right up and I could get 7200 rpm on the top and a "reliable" idle of about 2100. All this was without touching the factory set needle positions, just the throttle servo travel. The transition however left a lot to be desired. The throttle servo moved smoothly but the engine response was , for lack of a better term "jerky". As the throttle moved the engine would abruptly go from 2100 to say 4600-5200. I started trying to adjust the needle settings but regardless of what I did there was no discernible difference wherever I moved the high or low needles. I flew the plane but the engine was rough but it did not quit on me, there was just a very erratic transition. Temperature ranges on the engine indicated that it was not overheating anywhere so I don't believe it's an engine related issue. I have a Walbro that goes to a DLE 30 and I could try that but I want to know if there's anything I can do with the Tillotson before I replace it. Apologies if I have not clearly stated my problem but feel free to ask me for any clarification on the above.

Happy Flying!

Old 10-12-2015, 03:08 AM
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The engine is a turnigy so you have that working against you from the start.
Most new engines won't realize real good transition until after several tanks of fuel.
Trouble with transition from idle to mid-range is typically the low speed needle setting or it can also be bad geometry with the mechanical throttle linkage.
If you watch the carb butterfly as you increase throttle it should be moving immediately with no delay or dead spots. Sometimes you have to program a throttle curve to smooth it out.
Old 10-12-2015, 04:12 PM
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The carburetor is most likely a Chinese copy of a Walbro and just has the name Tillotson cast on it? They normally work well.

Also your running description sounds like the no advance or all advance of a model #4 RCEXL ignition module. They didn't have a advance curve. But likely the ignition module is also a Chinese copy of a Chinese RCEXL ignition on a Chinese engine that is a copy of another Chinese engine?

Old 10-12-2015, 06:51 PM
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But I would first try to open the low speed needle a little and see what happens?
Old 10-12-2015, 08:21 PM
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Do not assume the "factory" needle settings are worth any more than what it will take to start the engine. It must then be tuned - to your prop, altitude, air temperature, etc. There is no way on earth the needles could be preset taking all or much of any of that into account.

Rather than write out the tuning process again, here's a link to the tuning and some other notes I wrote out a while back. There's also a wealth of other info in that same string you might have a look through once as well.

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