OS .37 Carburetor Slop
10-13-2009, 08:27 AM
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OS .37 Carburetor Slop
Purchased a used Raptor 30 with an OS 37 a few months ago and have been having some tuning issues as of late. While pulling the carb apart for cleaning I noticed a fair amount of slop between 25%-75% throttle. I found this Youtube video where the user experienced the exact same slop, but according to him, it was the result of a manufacturing defect. I was just wondering if others have experienced this on OS 37 or if it is indeed a manufacturing defect and I have a bad carb.
Thanks,
Rick
[youtube]http://www.youtube.com/watch?v=qwVUQRp4zSo[/youtube]
Thanks,
Rick
[youtube]http://www.youtube.com/watch?v=qwVUQRp4zSo[/youtube]
10-14-2009, 09:30 AM
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RE: OS .37 Carburetor Slop
That video is so poor that I couldn't see a thing...too dark.
A small amount of movement is normal in most carbs. However, if vibration causes excessive wear, then it's possible that the in/out movement is too much and the settings can be compromised. Usually, though, you'll see problems with low-end mixture changing when you have the idle needle move in and out with the carb barrel...not the way the carb on the O.S. Max .37 SZ-H engine works.
You haven't said what your tuning difficulties are. That would be the clue to determining the cause.
A small amount of movement is normal in most carbs. However, if vibration causes excessive wear, then it's possible that the in/out movement is too much and the settings can be compromised. Usually, though, you'll see problems with low-end mixture changing when you have the idle needle move in and out with the carb barrel...not the way the carb on the O.S. Max .37 SZ-H engine works.
You haven't said what your tuning difficulties are. That would be the clue to determining the cause.
10-15-2009, 05:36 AM
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RE: OS .37 Carburetor Slop
I know that it is hard to see inside the carb due to the lighting but you can clearly see the side-to-side movement exhibited when the carb is at mid throttle. My question is, is this amount of side-to-side movement normal for the OS .37? This is my first nitro heli and because I bought it used, I have no idea how a new OS .37 is supposed to behave. My motor has as much and maybe more side-to-side play in the carb and you can clearly see that the air intake is made larger/smaller by this movement. Even with my limited experience with nitro engines it seems to me that any vibration could cause this movement to happen during flight making it almost impossible to achieve any kind of consistent tuning.
To answer your question about my particular tuning problems, I had been having an issue with the engine leaning out after several minutes of flight. After finding a small hole in the pressure line from the muffler I thought I had the problem solved but even after replacing all the fuel and clunk lines, cleaning the fule filter and fuel inlet, as well as replacing the glow plug, the problem persisted. The other day while testing, I was experiencing inconsistent rpms right from the start of my flight. The rpms seem to jump up and down in the mid-range without any input change from the transmitter. Another pilot at my flying field pointed out the amount of side-to side play in the carburetor in the mid-range. He pointed out that a lot of carbs have springs to eliminate the side-to-side play but that the OS .37 does not use one.
To answer your question about my particular tuning problems, I had been having an issue with the engine leaning out after several minutes of flight. After finding a small hole in the pressure line from the muffler I thought I had the problem solved but even after replacing all the fuel and clunk lines, cleaning the fule filter and fuel inlet, as well as replacing the glow plug, the problem persisted. The other day while testing, I was experiencing inconsistent rpms right from the start of my flight. The rpms seem to jump up and down in the mid-range without any input change from the transmitter. Another pilot at my flying field pointed out the amount of side-to side play in the carburetor in the mid-range. He pointed out that a lot of carbs have springs to eliminate the side-to-side play but that the OS .37 does not use one.
10-15-2009, 09:26 AM
#4
My Feedback: (11)
RE: OS .37 Carburetor Slop
Leaning out after several minutes of flight would not be carburetor-related. Erratic running at a part-throttle setting might be related to the carb.
When an engine leans after several minutes of flight, it almost always a fuel system-related problem. Usually, the fuel gets down low-enough in the tank that it will vibrate and have air get agitated into it. That leans the mixture. Also, the engine may not be getting adequate cooling and it gradually heats up. Overheating can sound and act a lot like overleaning. That's because an overlean condition causes the engine to overheat.
If the mixture is moving all around when you're at any given throttle setting, it's possible the carb is the culprit. The movement of the barrel in the body can make the idle needle move in and out of the fuel port inside the venturi. Many carbs have a spring to help keep the barrel pressed out. In the case of the heli carbs, the throttle linkage usually is enough to keep the carb barrel from moving in and out...that's because two arms are usually used with two pushrods. They provide the stability you want.
The movement is very typical of model engine carbs, and movement of a few thousandths is not uncommon. Yes, it wil be visible, but is usually not a problem. We don't see much that's related to the carb, itself.
When an engine leans after several minutes of flight, it almost always a fuel system-related problem. Usually, the fuel gets down low-enough in the tank that it will vibrate and have air get agitated into it. That leans the mixture. Also, the engine may not be getting adequate cooling and it gradually heats up. Overheating can sound and act a lot like overleaning. That's because an overlean condition causes the engine to overheat.
If the mixture is moving all around when you're at any given throttle setting, it's possible the carb is the culprit. The movement of the barrel in the body can make the idle needle move in and out of the fuel port inside the venturi. Many carbs have a spring to help keep the barrel pressed out. In the case of the heli carbs, the throttle linkage usually is enough to keep the carb barrel from moving in and out...that's because two arms are usually used with two pushrods. They provide the stability you want.
The movement is very typical of model engine carbs, and movement of a few thousandths is not uncommon. Yes, it wil be visible, but is usually not a problem. We don't see much that's related to the carb, itself.
