912ULS fuel starvation in steep turns
in General Tech Discussion
9 years ago
Dear Rotaxowners
I am at my wit`s end. I have recently installed a used 912ULS in my CGS Hawk II, replacing the 912 UL that was in it. When I do steep (60°+) turns at full throttle, the engine misfires quite seriously - it sounds like fuel starvation. After returning to wings level the problem disappears after a few seconds. It only happens at full throttle. The prop is adjusted to turn at about 5,500rpm at low airspeed. When I throttle back slightly (engine speed remains at 5,500rpm, but the engine sounds less strained), The Problem disappears.
This is what I tried:
* Installed a fuel return line from the clamp block (fuel distributor) to the mechanical pump suction side. I cannot return to before the gascolator because that would mean returning fuel that has already been metered. Air that is in the system stays in the return line, because it is the highest point. I have a backup electrical pump in parallel to the mechanical pump. Switching it on doesn`t make The Problem disappear.
* Cleaned and checked the carburetors. Needle circlip is in the correct position, the correct jets are installed, the float level looks good and is the same in both bowls.
* Exchanged the throttle valve spring and membrane with the old 912.
* Balanced the carbs.
* Checked the plugs, they look OK (dark brown or black, I fly unleaded Mogas) and they all fire. Rev drop between ignition circuits is about 150rpm at 4,000 rpm.
* Purged all visible air from the fuel lines. The lines from the clamp block to the carbs is not transparent, but I tried my best to get that air out too. Replaced all hose clamps and made sure they're tight. Still, after an hour´s flight there is air in the return line again. Cannot come from the tank, cannot come from any leaking connection.
Other details:
* My fuel pressure sensor is broken, can't say whether the fuel pressure is good or not. It certainly squirts far enough with just the electrical pump engaged.
* I'm not happy with my EGTs (a recording is attached). On full throttle the difference between cylinder 1 and 3 is nearly 150°C (!), at part throttle the difference is smaller. Note that when The Problem occurred, EGT for cylinder #2 (green line) collapses. Strange, on full throttle cylinder 2 runs hottest, at part throttle (4,400rpm) it is the coolest.
Blue skies
Arthur
I am at my wit`s end. I have recently installed a used 912ULS in my CGS Hawk II, replacing the 912 UL that was in it. When I do steep (60°+) turns at full throttle, the engine misfires quite seriously - it sounds like fuel starvation. After returning to wings level the problem disappears after a few seconds. It only happens at full throttle. The prop is adjusted to turn at about 5,500rpm at low airspeed. When I throttle back slightly (engine speed remains at 5,500rpm, but the engine sounds less strained), The Problem disappears.
This is what I tried:
* Installed a fuel return line from the clamp block (fuel distributor) to the mechanical pump suction side. I cannot return to before the gascolator because that would mean returning fuel that has already been metered. Air that is in the system stays in the return line, because it is the highest point. I have a backup electrical pump in parallel to the mechanical pump. Switching it on doesn`t make The Problem disappear.
* Cleaned and checked the carburetors. Needle circlip is in the correct position, the correct jets are installed, the float level looks good and is the same in both bowls.
* Exchanged the throttle valve spring and membrane with the old 912.
* Balanced the carbs.
* Checked the plugs, they look OK (dark brown or black, I fly unleaded Mogas) and they all fire. Rev drop between ignition circuits is about 150rpm at 4,000 rpm.
* Purged all visible air from the fuel lines. The lines from the clamp block to the carbs is not transparent, but I tried my best to get that air out too. Replaced all hose clamps and made sure they're tight. Still, after an hour´s flight there is air in the return line again. Cannot come from the tank, cannot come from any leaking connection.
Other details:
* My fuel pressure sensor is broken, can't say whether the fuel pressure is good or not. It certainly squirts far enough with just the electrical pump engaged.
* I'm not happy with my EGTs (a recording is attached). On full throttle the difference between cylinder 1 and 3 is nearly 150°C (!), at part throttle the difference is smaller. Note that when The Problem occurred, EGT for cylinder #2 (green line) collapses. Strange, on full throttle cylinder 2 runs hottest, at part throttle (4,400rpm) it is the coolest.
Blue skies
Arthur
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