os 91 fx, no issues
02-15-2006 | 10:31 AM
#1
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Senior Member
os 91 fx, no issues
I`ve been reading all about the remote needle issues on the "old " 91 fx. I happen to have one of these, with the needle and backplate in one casting. should I have any issues with this engine??? cause I dont. Mine runs great and dont overheat, but I have only been running it in 3-d planes so far. this doesn`t put much stress on the engine as I mostly float gently around at half trottle or less.full trottle is only used in short bursts when pulling out of hover. Where I am going with all this is that I wonder if all the "old" ones have issues when run hard enough or if I maybe have a good one that never will develop these problems. In case I too get problems would separating the remote needle from the backplate with some "dremelling" fix things? as I`ve read that problems is caused by heat transfer from the backlate to the needle assembly causing the fuel to waporisate and boil thereby the bubbles in the fuel line between the needle and carb.
02-15-2006 | 10:53 AM
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From: New Richmond,
WI
RE: os 91 fx, no issues
ORIGINAL: asmund
I`ve been reading all about the remote needle issues on the "old " 91 fx. I happen to have one of these, with the needle and backplate in one casting. should I have any issues with this engine??? cause I dont. Mine runs great and dont overheat, but I have only been running it in 3-d planes so far. this doesn`t put much stress on the engine as I mostly float gently around at half trottle or less.full trottle is only used in short bursts when pulling out of hover. Where I am going with all this is that I wonder if all the "old" ones have issues when run hard enough or if I maybe have a good one that never will develop these problems. In case I too get problems would separating the remote needle from the backplate with some "dremelling" fix things? as I`ve read that problems is caused by heat transfer from the backlate to the needle assembly causing the fuel to waporisate and boil thereby the bubbles in the fuel line between the needle and carb.
I`ve been reading all about the remote needle issues on the "old " 91 fx. I happen to have one of these, with the needle and backplate in one casting. should I have any issues with this engine??? cause I dont. Mine runs great and dont overheat, but I have only been running it in 3-d planes so far. this doesn`t put much stress on the engine as I mostly float gently around at half trottle or less.full trottle is only used in short bursts when pulling out of hover. Where I am going with all this is that I wonder if all the "old" ones have issues when run hard enough or if I maybe have a good one that never will develop these problems. In case I too get problems would separating the remote needle from the backplate with some "dremelling" fix things? as I`ve read that problems is caused by heat transfer from the backlate to the needle assembly causing the fuel to waporisate and boil thereby the bubbles in the fuel line between the needle and carb.
Of the 9 I have personally had or buddies have had, not even one of them had any problems. 6 of them are set up with bisson pitts muffler. They are all the old style. They just keep going and going like Energizer rabbits putting out the power.
02-15-2006 | 11:48 AM
#4
RE: os 91 fx, no issues
I think the best you can do try if your engine is overheating is to run it full throttle for 3-4min. on your 3d plane.
If it is overheating and there is nothing to do with the cowl(...),order the replacement backplate and needle valve assembly.
I bought mine a few weeks ago and it has the replacement parts on it.
I haven't try it though to see how it works.
I think it will be fine!
Enjoy.
Kostas
If it is overheating and there is nothing to do with the cowl(...),order the replacement backplate and needle valve assembly.
I bought mine a few weeks ago and it has the replacement parts on it.
I haven't try it though to see how it works.
I think it will be fine!
Enjoy.
Kostas
02-15-2006 | 12:37 PM
#5
Thread Starter
Senior Member
RE: os 91 fx, no issues
I`ll just keep running it and see. But wasn`t the problems that is reported on this forum because of overheating of the needle assembly or do I remember wrong?. If it is because of heat it then must come from the crankcase and backplate as this is the only connection between the needle assembly and the engine itself. Or was it just plain old airleaks that caused this bubbeling in a lot of engines?
02-15-2006 | 12:47 PM
#7
RE: os 91 fx, no issues
ORIGINAL: asmund
I`ll just keep running it and see. But wasn`t the problems that is reported on this forum because of overheating of the needle assembly or do I remember wrong?. If it is because of heat it then must come from the crankcase and backplate as this is the only connection between the needle assembly and the engine itself. Or was it just plain old airleaks that caused this bubbeling in a lot of engines?
I`ll just keep running it and see. But wasn`t the problems that is reported on this forum because of overheating of the needle assembly or do I remember wrong?. If it is because of heat it then must come from the crankcase and backplate as this is the only connection between the needle assembly and the engine itself. Or was it just plain old airleaks that caused this bubbeling in a lot of engines?
02-15-2006 | 01:07 PM
#8
My Feedback: (21)
RE: os 91 fx, no issues
The fact that the needle valve assy. was fastened to rear of the engine could
account for some vibration....but rather the leaky needle valve that produced
the bubbles, and some leaning out of the engine was the main problem. This
was cured in a lot of cases by mounting the n/v in a different location, or replacing
the leaky/bubbly one with another brand. K&B was a good replacement.
The needle valve was only part of the problems, which were exasperated by
factors induced by the engine owners.....fuel, props, mufflers, cowlings ect.
FBD.
account for some vibration....but rather the leaky needle valve that produced
the bubbles, and some leaning out of the engine was the main problem. This
was cured in a lot of cases by mounting the n/v in a different location, or replacing
the leaky/bubbly one with another brand. K&B was a good replacement.
The needle valve was only part of the problems, which were exasperated by
factors induced by the engine owners.....fuel, props, mufflers, cowlings ect.
FBD.
02-15-2006 | 01:15 PM
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From: Brighton,
MI
RE: os 91 fx, no issues
I have three of these motors and I do have overheating problems if I run full throttle for more than 3 or 4 minutes. All of mine are fully cowled with baffles and pitts mufflers which drastically contribute to the heating problem (IMHO). I can reduce or eliminate the overheating problem if fly mostly at 1/2 throttle with short bursts or moments at full. I changed all of them over to the new needle valve/body assembly so we'll see if this solves the problem when flying season starts again in a couple months.
02-15-2006 | 04:13 PM
#11
Senior Member
RE: os 91 fx, no issues
I have 2 91 FX's.If you get fine bubbles in the fuel line after the needle valve, cutting the needle valve off with a dremel tool will solve your problem.Heat transfer is the problem.
