Couple questions
07-17-2003, 11:26 PM
#1
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Couple questions
Greeting, I have a couple of questions.
1) I have an OS .61 FX on a Hog-Bipe and I keep loosing the back end of the muffler. This will be the third muffler that I am going to have to buy. At $40 dollars a piece it is getting expensive. The problem is, is that the bolt that holds the tail cone to the front half is fatiguing and breaks off in flight and the tail cone is lost in the woods. Is this a common problem? What do you suggest that I do to fix it? I suspect that vibration is the culprit, so I'm careful about getting the prop balanced correctly.
also,
2) I have an OS 120 II Surpass pumped. I purchased it back in the mid-80's. I have constantly have had problems with the engine running lean and dying out while in flight. I typically run Omega cool-power 10%. I'm running a 16-6 prop. I have tuned the engine to top RPM using my tach and then backed it down per the instructions. Earlier this year, while at the AMA homecoming at Muncie, one of the guys who seemed to know more about 4-strokes than me, disconnected the pump had me run 5% and that seemed to help. At least I got a flight in without the engine dying in flight. My question is, What do you think about disconnecting the pump? and do you have any tuning recommendations for this engine, or least an updated manual?
Thanks in advance
1) I have an OS .61 FX on a Hog-Bipe and I keep loosing the back end of the muffler. This will be the third muffler that I am going to have to buy. At $40 dollars a piece it is getting expensive. The problem is, is that the bolt that holds the tail cone to the front half is fatiguing and breaks off in flight and the tail cone is lost in the woods. Is this a common problem? What do you suggest that I do to fix it? I suspect that vibration is the culprit, so I'm careful about getting the prop balanced correctly.
also,
2) I have an OS 120 II Surpass pumped. I purchased it back in the mid-80's. I have constantly have had problems with the engine running lean and dying out while in flight. I typically run Omega cool-power 10%. I'm running a 16-6 prop. I have tuned the engine to top RPM using my tach and then backed it down per the instructions. Earlier this year, while at the AMA homecoming at Muncie, one of the guys who seemed to know more about 4-strokes than me, disconnected the pump had me run 5% and that seemed to help. At least I got a flight in without the engine dying in flight. My question is, What do you think about disconnecting the pump? and do you have any tuning recommendations for this engine, or least an updated manual?
Thanks in advance
07-18-2003, 01:44 PM
#2
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Couple questions
Losing the rear half of an O.S. muffler usually happens after the postion of the tail cone has been changed. Usually, the long bolt is tightened-up and the locking nut put on. A few flights later, the long bolt breaks.
What happens is that the long bolt is over-tightened, and then the engine's heat expands the muffler. After a few cycles, the long steel bolt, which doesn't expand as much as the aluminum muffler body, fatigues and breaks.
The "secret" is to tighten the long bolt just enough to keep the rear of the muffler from turning. Then apply the locking bolt.
For the FS-120 Surpass, the proper way to adjust the engine is to lean it as far as possible without detonation or RPM drop and leave it there. The main problem is too-rich running. If the engine tends to lean in flight, though, then the problem is likely elsewhere, or there's a blockage in the fuel system somewhere.
The pump carb really doesn't do well without the pump, since it's bore is large enough to cause fuel draw problems.
The only instructions available are those that came with the engine.
What happens is that the long bolt is over-tightened, and then the engine's heat expands the muffler. After a few cycles, the long steel bolt, which doesn't expand as much as the aluminum muffler body, fatigues and breaks.
The "secret" is to tighten the long bolt just enough to keep the rear of the muffler from turning. Then apply the locking bolt.
For the FS-120 Surpass, the proper way to adjust the engine is to lean it as far as possible without detonation or RPM drop and leave it there. The main problem is too-rich running. If the engine tends to lean in flight, though, then the problem is likely elsewhere, or there's a blockage in the fuel system somewhere.
The pump carb really doesn't do well without the pump, since it's bore is large enough to cause fuel draw problems.
The only instructions available are those that came with the engine.
