When good engines go bad...
01-19-2017, 05:59 PM
#1
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When good engines go bad...
For 5 seasons, I've had a CMPro Giles 202 with a GMS 1.20 that was just perfect. Despite the lousy rep of the GMS motors, this one was a peach. It started every time, ran perfectly, smoothly, and hauled the plane around nicely. The old G202 was my go-to bird for any situation.
I took the plane out for a day at the field, and it started up just like it always had. After running it up, I taxied out to the runway, but it suddenly quit. Weird, that's never happened. A buddy of mine said I had a dead glow plug. We swapped it, and the motor started right up. It quit again when I tried to taxi out. "Just richen the needle!" Did that, and it seemed to run OK. Taxi out, take off, and on the downwind, it quits. I make it back to the pavement and decide to take the plane home to figure it out.
Back at the ranch, I can't get it to run right. I change plugs, try different fuels, check the tank, pull the engine apart, reset the high speed needle, no luck. It will idle endlessly, but sputters at transition, flames out at speed. I open up the high speed, and it runs better, but loads up badly at mid throttle. Finally, I decide to check the low-speed - despite the smooth idle, it might be lean. And then I discover that the low-speed idle is very loose and moves easily. The movement of the throttle detunes the motor every time. The little O-ring that acted as a "lock" on the movement of the screw has dried out and shrunk, and the idle needle is free to move around as it pleases. I feel like a chump for not checking this earlier.
Ah well. Replaced the O-ring and all is well with the world. It's the little things that get you...
I took the plane out for a day at the field, and it started up just like it always had. After running it up, I taxied out to the runway, but it suddenly quit. Weird, that's never happened. A buddy of mine said I had a dead glow plug. We swapped it, and the motor started right up. It quit again when I tried to taxi out. "Just richen the needle!" Did that, and it seemed to run OK. Taxi out, take off, and on the downwind, it quits. I make it back to the pavement and decide to take the plane home to figure it out.
Back at the ranch, I can't get it to run right. I change plugs, try different fuels, check the tank, pull the engine apart, reset the high speed needle, no luck. It will idle endlessly, but sputters at transition, flames out at speed. I open up the high speed, and it runs better, but loads up badly at mid throttle. Finally, I decide to check the low-speed - despite the smooth idle, it might be lean. And then I discover that the low-speed idle is very loose and moves easily. The movement of the throttle detunes the motor every time. The little O-ring that acted as a "lock" on the movement of the screw has dried out and shrunk, and the idle needle is free to move around as it pleases. I feel like a chump for not checking this earlier.
Ah well. Replaced the O-ring and all is well with the world. It's the little things that get you...
01-20-2017, 07:52 AM
#5
Good trouble shooting job
The engine was just going to a lean mixture with the movememt of the NV And causing the engine to heat and die on you
NVs moving freely on the high or low end does happen from time to time
You can use a piece of fuel tubing on the high side as it prevents some movement and helps to seal any air gap there to increase the suction from the fuel tank
Use fuel tubing over fuel tubing on all fuel line connections for that same reason
Glo engines draw fuel by causing a vacuum in the crankcase to draw fuel from the tank so a sealed system is best
The engine was just going to a lean mixture with the movememt of the NV And causing the engine to heat and die on you
NVs moving freely on the high or low end does happen from time to time
You can use a piece of fuel tubing on the high side as it prevents some movement and helps to seal any air gap there to increase the suction from the fuel tank
Use fuel tubing over fuel tubing on all fuel line connections for that same reason
Glo engines draw fuel by causing a vacuum in the crankcase to draw fuel from the tank so a sealed system is best
The fuel tubing over the needle valve trick turned the TT.07 in this pic from unusable to an absolute joy to run . Yep , it's the little details that sometimes mean the most .
