Chris Engler
Active Member
I posted last week after a first start regarding some issues with a CS WW prop not moving and the XP-400 coughing /stumbling at high RPM. Happy to say the prop issue is resolved but the engine stumble is still a mystery. The engine is new and the fuel system is the standard Silver Hawk EX-5VA1. The ignition system is standard mags with the G3i system.
The engine starts and runs perfectly until 2400 RPM then if the throttle is advanced further, the engine will cough/sputter. If the mixture is leaned (about half travel on the throttle quadrant) I can keep the engine from running rough and at full throttle maintain around 2600 RPM.
All EGT/CHT readings are in the green and fuel flow is 18-19 gph at full throttle.
At 2400 RPM (just before sputtering) and full rich, when I lean, EGTs increase by about 150 degrees to peak and EGT spread is around 50 degrees hottest to coldest.
The coughing is present with the G3i ignition system switched both on and off so we don't believe that's a factor. Since I can lean to eliminate the cough at full throttle, I assume the mixture is simply too rich but there's no adjustment for full throttle mixture.
I've spoken to the folks at Precision a couple of times and they're stumped as well. Yesterday I pulled the FI system off the engine and shipped it to them for bench testing.
Thought I'd post here to see it anyone knowledgeable with the Silver Hawk servo has any ideas....
Thanks!
The engine starts and runs perfectly until 2400 RPM then if the throttle is advanced further, the engine will cough/sputter. If the mixture is leaned (about half travel on the throttle quadrant) I can keep the engine from running rough and at full throttle maintain around 2600 RPM.
All EGT/CHT readings are in the green and fuel flow is 18-19 gph at full throttle.
At 2400 RPM (just before sputtering) and full rich, when I lean, EGTs increase by about 150 degrees to peak and EGT spread is around 50 degrees hottest to coldest.
The coughing is present with the G3i ignition system switched both on and off so we don't believe that's a factor. Since I can lean to eliminate the cough at full throttle, I assume the mixture is simply too rich but there's no adjustment for full throttle mixture.
I've spoken to the folks at Precision a couple of times and they're stumped as well. Yesterday I pulled the FI system off the engine and shipped it to them for bench testing.
Thought I'd post here to see it anyone knowledgeable with the Silver Hawk servo has any ideas....
Thanks!