Strange behavior from my engine today...
Today I decided, for the first time since I've owned it, to fly my UltraStar to another airport about 10 miles away. Previously all my flights have been in the close vicinity of my home field. Anyway, 'bout 10-15 minutes into the flight, cruising at 5700 rpm and 3000', I lost power. It didn't actually quit; it was more like it was just throttled back suddenly. My hand at the moment wasn't on the throttle but on my lap, keeping warm. Without thinking to check where the throttle was, I reached down and pushed it forward, and I instantly had full power again. Temps were normal.
My first thought was that the throttle friction lock had slipped, but to be safe I headed back home. The engine continued to run normally, so I just flew around for another 5 minutes or so over the airport, letting the plane slowly climb to about 3500', then reduced power to about 3000 rpm to descend at cruise airspeed. After a minute or two of this, the engine just... quit. I wasn't too alarmed as I was right over the airport, so I tried to restart. Several pulls and nothing, then a couple shots of prime, and finally it caught and started at full throttle, but with no power. Too much prime, perhaps, as jockeying the throttle a few times brought it back to normal power, and I had no further trouble, though I landed as soon as possible.
On the ground, the engine ran fine at all throttle settings from idle to WOT. Killed the ignition at 5500 and checked the plugs; I would say they were too light except that they were brand new before this flight. Wiggled the wires while running, no hint of trouble there.
This is the [Cuyuna] ULII-02 engine, low hours, Mikuni carb, jetted (310 main jet) per manufacturer's specs for sea level (where my airport is) at 40-60°F (temps today were around 60), and the plug color previously indicated the specs are appropriate. Running 93 octane auto gas (switched from 100LL a few weeks ago). The new plugs were the only change since the last flight (the old plugs were fine but I wanted to replace them with solid terminal plugs). The only other odd thing was the plugs were slightly too loose (when I installed them after the last flight I was using a different wrench and didn't tighten them enough), but they weren't _loose_, just not properly torqued. The only other odd thing I noticed (or perhaps not odd, just never noticed before) is that in flight (but not on the ground) it didn't want to seem to hold exactly 3000 rpm, and the EGT fluctuated a bit at that rpm.
Others have suggested carb ice (not a common problem on 2-strokes but quite possible at 65° air temp and 40° dewpoint, never heard of an abrupt failure from ice at cruise power), fuel (though the filter is clean as a whistle and I have two separate tanks in parallel). Water in the fuel, perhaps? Non visible on the ground but I supposed it could have separated out as I climbed into cooler air.
At this point I'm a bit nervous... and open to ideas.
-Dana
"Very funny, Scotty. Now beam down my clothes."
Today I decided, for the first time since I've owned it, to fly my UltraStar to another airport about 10 miles away. Previously all my flights have been in the close vicinity of my home field. Anyway, 'bout 10-15 minutes into the flight, cruising at 5700 rpm and 3000', I lost power. It didn't actually quit; it was more like it was just throttled back suddenly. My hand at the moment wasn't on the throttle but on my lap, keeping warm. Without thinking to check where the throttle was, I reached down and pushed it forward, and I instantly had full power again. Temps were normal.
My first thought was that the throttle friction lock had slipped, but to be safe I headed back home. The engine continued to run normally, so I just flew around for another 5 minutes or so over the airport, letting the plane slowly climb to about 3500', then reduced power to about 3000 rpm to descend at cruise airspeed. After a minute or two of this, the engine just... quit. I wasn't too alarmed as I was right over the airport, so I tried to restart. Several pulls and nothing, then a couple shots of prime, and finally it caught and started at full throttle, but with no power. Too much prime, perhaps, as jockeying the throttle a few times brought it back to normal power, and I had no further trouble, though I landed as soon as possible.
On the ground, the engine ran fine at all throttle settings from idle to WOT. Killed the ignition at 5500 and checked the plugs; I would say they were too light except that they were brand new before this flight. Wiggled the wires while running, no hint of trouble there.
This is the [Cuyuna] ULII-02 engine, low hours, Mikuni carb, jetted (310 main jet) per manufacturer's specs for sea level (where my airport is) at 40-60°F (temps today were around 60), and the plug color previously indicated the specs are appropriate. Running 93 octane auto gas (switched from 100LL a few weeks ago). The new plugs were the only change since the last flight (the old plugs were fine but I wanted to replace them with solid terminal plugs). The only other odd thing was the plugs were slightly too loose (when I installed them after the last flight I was using a different wrench and didn't tighten them enough), but they weren't _loose_, just not properly torqued. The only other odd thing I noticed (or perhaps not odd, just never noticed before) is that in flight (but not on the ground) it didn't want to seem to hold exactly 3000 rpm, and the EGT fluctuated a bit at that rpm.
Others have suggested carb ice (not a common problem on 2-strokes but quite possible at 65° air temp and 40° dewpoint, never heard of an abrupt failure from ice at cruise power), fuel (though the filter is clean as a whistle and I have two separate tanks in parallel). Water in the fuel, perhaps? Non visible on the ground but I supposed it could have separated out as I climbed into cooler air.
At this point I'm a bit nervous... and open to ideas.
-Dana
"Very funny, Scotty. Now beam down my clothes."
