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YS FZ 140 Sport Throttle Barrel Seizing

Old 06-10-2013, 08:26 PM
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Default YS FZ 140 Sport Throttle Barrel Seizing

I have a YS FZ 140 Sport that is now in its 4th season of use in a KMP Spitfire. It has been working almost flawlessly until last month when the throttle failed to reopen mid flight. I managed to land and on inspection back home I found that the bolt holding the throttle arm onto the carb barrel had come loose. I assumed that this was due to vibration and tightened it back into place. Yesterday was my first outing since then so prior to flying I ran the engine for a few minutes and shut the engine down to check that the throttle arm bolt was not backing out again. I was very surprised to find that the throttle barrel was binding to the extent that it stalled the digital throttle servo. As the engine cooled down the barrel freed up.

I removed the cowl and confirmed that the throttle link from the servo was not binding. I subsequently ran the engine again for an extended period of time and discovered that while the engine is running the throttle is at least free enough to operate normally. However, once stopped the throttle barrel freezes up until the engine cools. I did risk one flight without any problems. However, I suspect that my original problem was caused by a partially seizing barrel so that the arm worked loose and would like to fix the problem. I was wondering if anyone else has experienced similar problems on this or other YS engines and whether there is a simple remedy. I have put countless gallons of fuel through this engine in the same aircraft and configuration but it is possible that this has been occurring for some time and I just did not notice it.

Martin
Old 06-10-2013, 08:43 PM
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Default RE: YS FZ 140 Sport Throttle Barrel Seizing

I've seen this happen when the carb body is over tightened, or not uniformly tightened and it warps the bore enough to seize the barrel. you might want to pull the engine and loosen the body bolts to see if that frees things up and then retighten them.
Old 06-10-2013, 09:17 PM
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Default RE: YS FZ 140 Sport Throttle Barrel Seizing

Thanks I will give this a try. I have not touched this engine since new so the bolts are at the setting used when factory assembled. I will be travelling over the next few weeks so it will be a while before I can test the engine with the carb bolts reset.

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