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OS FS Surpass II bearing question

Old 07-04-2020, 05:00 AM
  #26  
ahdofu
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Replaced the O-rings for the mixture valve and needle. The old O-rings were somewhat stiff and it was relatively easy to change them. The needle does feel tighter now. Operationally, however, the engine is still erratic. I ran the engine and had peak RPM (~ 9300 RPM, 14x6 APC) at 1+ turns of the needle which is where it should have been. Switched to a MA 14x6 prop and the motor RPM cycled high/low and I had to open the needle to 2.25 turns before it stabilized again at 9300 RPM. I think there is a leak somewhere. My last hope is the O-ring for the carb to intake. I am yet to replace that part as it is yet to arrive.
Old 07-06-2020, 08:32 PM
  #27  
bigtim
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9300 isn't bad its what I have been seeing on my 1st bench runs of the 120 with a 15/6 prop.
after checking that carb/intake O ring to see if its hard or has a flattened side at the manifold my gasket looked OK in the carb body, but when I really looked at it after popping it out of the body there was a definite flat spot on the inside and the rubber was really stiff and felt old compared to the new one, I could tell there was a loose seal when the engine was running it wasn't smooth and consistent like yours,also the carb was pretty loose like it just slid onto the manifold with little to no effort after installing the new gasket it took a little work to get the carb on I am sure that was part of my erratic tuning.
on a more positive note on my other 120 with the pump, after resetting the screw on the back of the pump to match the one I have that had not been messed with, and installing the bearings, crank, piston, and pump, I got the pump to push fuel at a reasonable rate I still don't have accurate pressure numbers to work from but I am confident the engine will run, it's mostly assembled now I just need to go through the carb and adjust the valves, then I can get some runs in and see how she goes.
there is also a article from one of the engine guru's, Clarence Lee, about plumbing the fuel lines to reduce the pressure to the carb on these older pumpers to the return line so they don't get all floody and over fueled,at least I got the pump to move fuel thats a step once these old fuel pumps go bad there just parts engines.
Old 07-10-2020, 07:31 PM
  #28  
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This afternoon I received the O-ring for the carb/intake. In replacing the O-ring the intake manifold just slid out and once I had removed the old O-ring, I found it to be quite stiff. With the new O-ring installed, the manifold is now held tightly in place. Anyway ran the engine and everything seem to be in order. Peak RPM increased to 9600 and more importantly, the engine did not missbehave. I'll need more runs to convince myself that this was it but so far, all seem to be OK. Thank you for all your helpful comments.
Old 07-11-2020, 06:49 PM
  #29  
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I did several flights today and the engine did not misbehave at all. I also noticed that previously it was taking longer for the engine to start. Now it starts relatively quickly.
On a side note I am down to my last few ounces of glow fuel that I use with my OS engine (15% nitro/18% oil). I have some YS 20/20 fuel around. Have you ever tried YS 20/20 fuel with your OS engines?
Old 07-12-2020, 12:10 PM
  #30  
bigtim
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as I am led to believe as long as the oil content is around 18% you can run any fuel you want the higher Nito content makes the engine run better to a point, OS engines will run 5-20% nitro as long as the oil is 18% sometimes you need to tune them to the fuel change but otherwise should be fine, this 15% fuel I have used makes the engines easier to tune, they seem more responsive and smoother overall, when I use the lower nitro fuel they seem to be a little sluggish, as I understand it the oil is the biggest factor.
I have been super busy with work so I haven't had a chance to go to the field, we also have some restrictions in place that limits the members on any given day but I am looking forward to getting over there next week.
Old 07-12-2020, 05:16 PM
  #31  
ahdofu
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I will give it a try once I run out of my 15/18 OS fuel. Right now it really tough to get hold of any 15% nitro fuel in my area.
Old 07-25-2020, 07:11 PM
  #32  
ahdofu
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This afternoon I tried the YS 20/20 fuel. Peak RPM increased from ~ 9300 RPM to ~ 9600. Not a huge increase but idle improved a lot.The engine just purrs along at ~ 2000 RPM. Along the way I found it necessary to alter both the high speed and idle settings. High speed needle position changed from 1.5 turns to 2.5 turns. Idle screw is now around 30 deg more open (richer). I'll check on peak RPM next time I am at the field.
Old 08-01-2020, 07:34 PM
  #33  
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More testing done with YS 20/20 fuel. After two days of flying I am finding that high speed behavior is somewhat erratic. Idle is great though. This fuel is causing periodic oscillatory behavior at high RPMs. I am beginning to think that my OS engine may not be quite happy with YS 20/20 fuel. Of course I'll need to grab some 15/18 fuel and see whether the same oscillatory behavior is there or not.
Old 08-09-2020, 02:34 PM
  #34  
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Got some fresh 15/18 fuel and to my dismay the high speed oscillatory behavior is there. It is back to basics to see what is causing this.

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