Inverted OS 1.20AX in Seagull PC-9
10-01-2012, 04:16 PM
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Inverted OS 1.20AX in Seagull PC-9
Hello,
I have a new Seagull PC-9 1.20 with a new OS 1.20AX installed. Anyone familiar with this airplane knows the engine is mounted inverted and the fuel tank is positioned above the carb, with no practical possibility of re-orienting the tank. The rest of the engine setup consists of a JTec Radiowave wrap-around Pitts muffler, #8 glow plug, 10% nitro fuel, Perry VP-30 pump, and a 15x7 3-blade prop (I have tried a 2-blade prop with no change in my problems).
Originally I tried using just muffler pressure with no fuel pump. When trying to start the engine, fuel continuously dripped (fast drip) from the carb. Most of the time, the engine would not crank unless I flipped it upside down (motor right side up) while cranking. This would work and it would even idle and taxi pretty good, but shortly after takeoff, the engine would quit.
I then tried the Perry VP-30 first without the bypass modification. Again, fuel dripped from the carb, this time even faster (nearly steady stream). I backed off the pressure adjustment as far as the manual said I could, but still had the fast leak during cranking (the engine never started).
I then added the bypass modification by putting a T-fitting within ~1/4" from the fuel inlet of the carb and the "other" T-fitting ~1/2" from the outlet of the fuel filler valve (carb side). Fuel still dripped from the carb, but not as bad. The engine was still very hard to start, but finally started. I was unable to get a rich mixture even with the adjustment screw on the VP-30 pump turned in as far as the manual said it could go (not quite flush with the black plastic body). Now I am concerned the engine is hurt due to the excessively lean condition (on a side note, what are the obvious signs of a burnt motor?).
I know others have had success with this airframe and engine combo. Is there something obvious I am doing wrong?
When the engine does run, it 'bangs' pretty hard at idle, causing the airframe to sound like a drum. It 'bangs' hard enough that it knocked out the canopy screws and I am worried it is knocking the glue joints loose as well. This goes away above 25% throttle, but the engine still sounds rough compared to my OS 55AX, 46AX and 25MAX (I know these are different motors, but they all run very smooth compared to this one). Is this a characteristic of this motor or is that related to the tuning problem?
Thanks!!
I have a new Seagull PC-9 1.20 with a new OS 1.20AX installed. Anyone familiar with this airplane knows the engine is mounted inverted and the fuel tank is positioned above the carb, with no practical possibility of re-orienting the tank. The rest of the engine setup consists of a JTec Radiowave wrap-around Pitts muffler, #8 glow plug, 10% nitro fuel, Perry VP-30 pump, and a 15x7 3-blade prop (I have tried a 2-blade prop with no change in my problems).
Originally I tried using just muffler pressure with no fuel pump. When trying to start the engine, fuel continuously dripped (fast drip) from the carb. Most of the time, the engine would not crank unless I flipped it upside down (motor right side up) while cranking. This would work and it would even idle and taxi pretty good, but shortly after takeoff, the engine would quit.
I then tried the Perry VP-30 first without the bypass modification. Again, fuel dripped from the carb, this time even faster (nearly steady stream). I backed off the pressure adjustment as far as the manual said I could, but still had the fast leak during cranking (the engine never started).
I then added the bypass modification by putting a T-fitting within ~1/4" from the fuel inlet of the carb and the "other" T-fitting ~1/2" from the outlet of the fuel filler valve (carb side). Fuel still dripped from the carb, but not as bad. The engine was still very hard to start, but finally started. I was unable to get a rich mixture even with the adjustment screw on the VP-30 pump turned in as far as the manual said it could go (not quite flush with the black plastic body). Now I am concerned the engine is hurt due to the excessively lean condition (on a side note, what are the obvious signs of a burnt motor?).
I know others have had success with this airframe and engine combo. Is there something obvious I am doing wrong?
When the engine does run, it 'bangs' pretty hard at idle, causing the airframe to sound like a drum. It 'bangs' hard enough that it knocked out the canopy screws and I am worried it is knocking the glue joints loose as well. This goes away above 25% throttle, but the engine still sounds rough compared to my OS 55AX, 46AX and 25MAX (I know these are different motors, but they all run very smooth compared to this one). Is this a characteristic of this motor or is that related to the tuning problem?
Thanks!!
