I have a fairly new (less than a year old) OS .61FX mounted upright in a Twist 3D 60 with a 13x6 prop.  The engine has been properly broke in and has about 20 flights on it. I'm having a problem that I'm not sure how to solve.   When flying the plane at around 1/4 throttle, if I fly inverted, it will die and I have to dead-stick the plane to the ground. It doesn't seem to happen when I do this at 3/4 or higher throttle, but it does stutter from time to time, it just doesn't quit. I never have a problem whatsoever if I don't fly inverted ... runs through a tank of fuel just fine and I can do anything I want with the plane. At first, I thought the clunk was getting stuck and sucking air, but this is not the case. The clunk is free and not getting hung up anywhere ... also, when the plane lands dead-stick, upon inspection, there is fuel in the fuel line all the way to the carb with no air bubbles in it. Is there a way to correct this problem?  Anyone ever had this happen before?  I'm not sure where to start, I've never had this issue previously. I've tried leaning and richening the engine with the main needle valve (no difference - the problem is repeatable), and I've changed to a hotter glow plug (from an OS 8 to a 3) so far. I'm just not sure what's causing the condition, so I'm not sure what to try to fix it. Could the engine be flooding itself upside down somehow, causing the glow plug to foul out?  What would cause that and how can it be corrected? I pulled the glow plug after one of the dead-stick landings and it was not wet, but with a hot engine, I thought maybe it had evaporated after normal level flight had resumed (even though the engine was not running). Just not sure where to go with this and I'm searching for some ideas to try ....

Twist 3D 60 with a 13x6 prop.  The engine has been properly broke in and has about 20 flights on it. I'm having a problem that I'm not sure how to solve. When flying the plane at around 1/4 throttle, if I fly inverted, it will die and I have to dead-stick the plane to the ground. It doesn't seem to happen when I do this at 3/4 or higher throttle, but it does stutter from time to time, it just doesn't quit. I never have a problem whatsoever if I don't fly inverted ... runs through a tank of fuel just fine and I can do anything I want with the plane. At first, I thought the clunk was getting stuck and sucking air, but this is not the case. The clunk is free and not getting hung up anywhere ... also, when the plane lands dead-stick, upon inspection, there is fuel in the fuel line all the way to the carb with no air bubbles in it. Is there a way to correct this problem?  Anyone ever had this happen before?  I'm not sure where to start, I've never had this issue previously. I've tried leaning and richening the engine with the main needle valve (no difference - the problem is repeatable), and I've changed to a hotter glow plug (from an OS 8 to a 3) so far. I'm just not sure what's causing the condition, so I'm not sure what to try to fix it. Could the engine be flooding itself upside down somehow, causing the glow plug to foul out?  What would cause that and how can it be corrected? I pulled the glow plug after one of the dead-stick landings and it was not wet, but with a hot engine, I thought maybe it had evaporated after normal level flight had resumed (even though the engine was not running). Just not sure where to go with this and I'm searching for some ideas to try .... Like the other reply, I think that the fuel tank is probably set too low causing a tank high position when inverted. This can easily drown your engine with an overly rich mixture. I would set the tank up dead centre with the needle valve (had to for pattern flying where there is a lot of inverted and outside manoeuvres). Then very carefully adjust the low end mixture so that it isn't too rich. You have to make adjustments to both the low and high end mixtures as you are tuning. You know that you have the low end mixture pretty close if you have the engine at idle for several seconds and then pinch off the fuel line and the engine dies without a great increase in rpm. There should be a slight rpm increase before dying. Properly tuned there should be little to no hesitation when going from idle to full throttle. Good luck

I have a fairly new (less than a year old) OS .61FX mounted upright in a Twist 3D 60 with a 13x6 prop.  The engine has been properly broke in and has about 20 flights on it. I'm having a problem that I'm not sure how to solve.   When flying the plane at around 1/4 throttle, if I fly inverted, it will die and I have to dead-stick the plane to the ground. It doesn't seem to happen when I do this at 3/4 or higher throttle, but it does stutter from time to time, it just doesn't quit. I never have a problem whatsoever if I don't fly inverted ... runs through a tank of fuel just fine and I can do anything I want with the plane. At first, I thought the clunk was getting stuck and sucking air, but this is not the case. The clunk is free and not getting hung up anywhere ... also, when the plane lands dead-stick, upon inspection, there is fuel in the fuel line all the way to the carb with no air bubbles in it. Is there a way to correct this problem?  Anyone ever had this happen before?  I'm not sure where to start, I've never had this issue previously. I've tried leaning and richening the engine with the main needle valve (no difference - the problem is repeatable), and I've changed to a hotter glow plug (from an OS 8 to a 3) so far. I'm just not sure what's causing the condition, so I'm not sure what to try to fix it. Could the engine be flooding itself upside down somehow, causing the glow plug to foul out?  What would cause that and how can it be corrected? I pulled the glow plug after one of the dead-stick landings and it was not wet, but with a hot engine, I thought maybe it had evaporated after normal level flight had resumed (even though the engine was not running). Just not sure where to go with this and I'm searching for some ideas to try .... What Dave and Retread said, plus: For a diagnostic, why not put the plane on a stand and run it inverted on the ground, at the deadly throttle setting?  Then you can see what's going on close up, you can see if you can adjust the mixture to keep it going, you can maybe pinch the fuel tubing to see if it's too rich or lean (if it's too rich pinching the line will make it speed up, too lean it'll sag or die immediately instead of after a bit).

Twist 3D 60 with a 13x6 prop.  The engine has been properly broke in and has about 20 flights on it. I'm having a problem that I'm not sure how to solve.   When flying the plane at around 1/4 throttle, if I fly inverted, it will die and I have to dead-stick the plane to the ground. It doesn't seem to happen when I do this at 3/4 or higher throttle, but it does stutter from time to time, it just doesn't quit. I never have a problem whatsoever if I don't fly inverted ... runs through a tank of fuel just fine and I can do anything I want with the plane. At first, I thought the clunk was getting stuck and sucking air, but this is not the case. The clunk is free and not getting hung up anywhere ... also, when the plane lands dead-stick, upon inspection, there is fuel in the fuel line all the way to the carb with no air bubbles in it. Is there a way to correct this problem?  Anyone ever had this happen before?  I'm not sure where to start, I've never had this issue previously. I've tried leaning and richening the engine with the main needle valve (no difference - the problem is repeatable), and I've changed to a hotter glow plug (from an OS 8 to a 3) so far. I'm just not sure what's causing the condition, so I'm not sure what to try to fix it. Could the engine be flooding itself upside down somehow, causing the glow plug to foul out?  What would cause that and how can it be corrected? I pulled the glow plug after one of the dead-stick landings and it was not wet, but with a hot engine, I thought maybe it had evaporated after normal level flight had resumed (even though the engine was not running). Just not sure where to go with this and I'm searching for some ideas to try .... I agree with the others - the tank is set too low. Position the tank so that where the fuel line exits the stopper on the tank is even with the SPRAY BAR in the carb.  You MAY need to readjust the carb settings.

Storm