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OS91FX dies in flight - 5/19/2012 1:30 AM   
oldtyme


 

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Status: offline 		OK well broken in engine, made the needle valve fix that is required on these engines and it has been as reliable as it gets. Fires up on the first spin, idles fine, transition is fine, take off and 3 or 4 minutes later it dies..............what's up!

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RE: OS91FX dies in flight - 5/19/2012 2:05 AM   
SeamusG



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Status: offline 		What's the condition of the glow plug?


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RE: OS91FX dies in flight - 5/19/2012 2:08 AM   
oldtyme


 

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Status: offline 		Put a new one in last time...........an OS#8............which is what I've always run it on..........OH and 10% nitro.........PowerMaster

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RE: OS91FX dies in flight - 5/19/2012 2:35 AM   
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Status: offline 		how long has it been since you've checked the condition of the lines (clunk) in your tank?

Could be there's a hole, and after the tank gets empty partway, it's exposed, and you start sucking air.



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RE: OS91FX dies in flight - 5/19/2012 5:43 AM   
Turk1



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Status: offline 		Can this be the famous vapor lock case of OS 91FX?Is your remote needle assembly made of full metal?

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RE: OS91FX dies in flight - 5/19/2012 5:56 AM   
oldtyme


 

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Status: offline 		No Turk1............that's why I said that I had made the fix on the engine........new backplate, mounting bracket and needle valve assy from the OS65LA. Has been flying fine for the last two seasons and now this.

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RE: OS91FX dies in flight - 5/19/2012 8:20 AM   
NikolayTT


 

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Status: offline 		I assume you get tank pressure from the exhaust pipe and those few min. proper operation and then sudden death seems related to heat rumping up. I had some similar miserious behaviour and all dissapeared when changed the fuel to at least 20% oil and less(!) than 12% nitromethan. Later could go to 16% oil and 16% nitrometan in the expense of usig fuel pump. Cheers, Nick

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RE: OS91FX dies in flight - 5/19/2012 9:08 AM   
NikolayTT


 

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Status: offline 		Or simply speaking, the problem might be an interrupted pressure from the exhaust pipe, which is rather bulky for this engine; better get rid of it.

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RE: OS91FX dies in flight - 5/19/2012 4:12 PM   
SeamusG



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Status: offline 		OT - do you recall what throttle setting you were at and how the engine sounded before and whilte it cut out? Had you just backed off the throttle during a down line? Full throttle "birds look out" high speed pass? Did it just quit - WAAAAAAAA | silence. Or, WAAAAA uh WAAAA uh WAA uh WA uh | silence? I know the 2nd well - can't tune an engine to save my (or my plane's) life! But I did stay at a Motel 6 ...

Nikolay - why toss the exhaust system? Bulky just might result in quiet. Enquiring minds. That's all.


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RE: OS91FX dies in flight - 5/19/2012 5:32 PM   
NikolayTT


 

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Status: offline 		John,
I get lot of power fromthat engine without tosting it, just not
suffocating it = open exhaust to let it breting freely, nearly3.2bhp
on 13x8 and 12500. It is what keeps me not interested in electric ones.
And flying on a bg club field beside the real Extra-300 my noise is not
even noticed .

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RE: OS91FX dies in flight - 5/19/2012 5:38 PM   
JPMacG


 

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Status: offline 		Are you sure you don't have the carb and pressure tap fuel lines reversed? That's the sort of mistake I would make.

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RE: OS91FX dies in flight - 5/19/2012 5:49 PM   
David Bathe



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Status: offline 		Over heating?
Hows the cowl/intake/exit?


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RE: OS91FX dies in flight - 5/19/2012 8:17 PM   
yosephwhite


 

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Status: offline 		 Check/replace the fuel lines in and outside the tank. I do mine every 2-3 seasons it's a pain but better than dead sticking at a bad time (like any time is good!) Try removing the needle valve and running a thin wire like the wire in a bread tie through it. You may have picked up some dirt or sand that's partially cloging it. Clean the carb and blow out with compressed air or dust off I would do that to the needle valve too after the wire.
 Dirt or bad lines are the most likely cause as it was running fine before.
Good luck! 

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RE: OS91FX dies in flight - 5/19/2012 9:03 PM   
dbacque


 

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Status: offline 		As Fizzwater stated, check the condition of the lines in your tank. Every year or two I have the exact same problem. The cause is usually that the tubing in the tank has decomposed and either has a leak or has completely broken off. Open the tank and check the lines closely. You'll probably find that the tubing is gummy and sticky. And leaky! Get down to half tank and it sucks air. When you change the lines, also check you fuel filter, mine was plugged with little blue pieces of decomposed fuel tubing.

Dave

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RE: OS91FX dies in flight - 5/19/2012 9:40 PM   
pmerritt


 

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Status: offline 		I had the SAME exact issue with my OS.91.  I sent it off to that guy in Arizona, had it re-ringed, changed out the needle set up.  They adjusted the cylinder some.  New re-built. (he did an incredible job - no blame to him)  Put it back on my big U Can Do and it quit about 60 / 90 seconds in flight.  The ONLY blessing was it was a UCANDO and it floated forever dead stick after dead stick until I got so damned mad at the whole set up I sold the RTF for $150.00 and got rid of the headache.  Seems when you have one like ours, the best thing you can do with it is make a decent cat fish weight with it. 

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RE: OS91FX dies in flight - 5/19/2012 11:18 PM   
dszabo2


 

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Status: offline 		I have 1 91 FX that I struggled with for a summer with the exact issue. I finally cut the needle valve assmbly of the crankcase and mounted to the airframe. Its been atleast 4 years and its been a solid, reliable engine since the fix. I have a 2nd one that I put a perry carb in and it also works perfect.



Dave

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RE: OS91FX dies in flight - 5/20/2012 12:09 AM   
dbacque


 

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Status: offline 		By the way, I should have mentioned that the klunk tubing decomposition issue has happened to me on several planes including my Epsilon powered by an OS .91 FX. The symptoms Oldtyme describes in his first post exactly mirror the problems I had on the Epsilon when the klunk line fell apart and broke in two. Once the lines and filter are replaced the plane is usually good for another year or two of reliable service from the .91. I've made no mods to my engine, it's stock out of the box and I've never had problems with deadsticks other than when the tank lines fall apart, twice now in this plane.

Oldtyme says he had a couple of seasons of good service from his engine/setup. I really would open that tank and check the lines. Quick, easy and should be done every year.

Dave

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RE: OS91FX dies in flight - 5/20/2012 12:18 AM   
aspeed


 

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Status: offline 		Sometimes the clunk goes forward on a hard landing or from hanging nose down in the shop too.  Could be the vent blocked or just a bit too lean at he end of the tank.  They usually get that little bit leaner at the end of the flight, enough to kill it sometimes.

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RE: OS91FX dies in flight - 5/20/2012 1:24 AM   
SeamusG



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Status: offline 		Don't ya just love guessing?    So tough to toss solutions at a problem when the symptoms are not explained.

All of the suggestions could be fixes. Or not.

Let us know how your problem resolution is going!




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RE: OS91FX dies in flight - 5/20/2012 1:45 AM   
oldtyme


 

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Status: offline 		OK..........some very interesting suggestions. As far as overheating goes........it is on a GP Big Stick 60 so it is out in the breeze. I have done the needle valve fix for this engine. Like I said this just happened out of the blue last weekend. Then a thought came to me...............last weekend I was trying to finish up some fuel........not PowerMaster.........but Cool Power that I had had in my shop for 3+ years........at the cost of glow fuel these days, I was trying to milk every bit of fuel I had around. Well I just happened to have a brand new can of PowerMaster I bought a couple of weeks ago so I took that with me and used it instead............plane ran fine. I know that I have read from several different contributors that older fuel worked just fine........I'm telling you that that was all that changed and I flew today trouble free.......no different settings......nothing. I ignored the obvious

Thanks for all the suggestions though........

Andy

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RE: OS91FX dies in flight - 5/20/2012 3:09 AM   
aspeed


 

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Status: offline 		Or that too.  Good to see it working.

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RE: OS91FX dies in flight - 5/20/2012 3:20 AM   
pkoury


 

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quote:

ORIGINAL: oldtyme

OK..........some very interesting suggestions. As far as overheating goes........it is on a GP Big Stick 60 so it is out in the breeze. I have done the needle valve fix for this engine. Like I said this just happened out of the blue last weekend. Then a thought came to me...............last weekend I was trying to finish up some fuel........not PowerMaster.........but Cool Power that I had had in my shop for 3+ years........at the cost of glow fuel these days, I was trying to milk every bit of fuel I had around. Well I just happened to have a brand new can of PowerMaster I bought a couple of weeks ago so I took that with me and used it instead............plane ran fine. I know that I have read from several different contributors that older fuel worked just fine........I'm telling you that that was all that changed and I flew today trouble free.......no different settings......nothing. I ignored the obvious

Thanks for all the suggestions though........

Andy

Just started reading this thread and first thing I thought of was bad fuel. Any time a fine running engine suddenly goes sour I replace the glow plug (even if it glows bright on the ni-starter) and then try fresh fuel. If either of those wont solve the problem then its off we go to the tank, fuel line, muffler pressure, trash in the system, sacrafice a cat, stay at a Holiday in......and if nothing else works fly a specktrum radio and when you plant a plane the balky engine is forgotten

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RE: OS91FX dies in flight - 5/20/2012 4:12 AM   
WRM


 

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Status: offline 		IT is vapor locking . All the FXs do it . That is the reason OS moved the needle valve to the carburetor . There was an article in Model Airplane News a couple of years ago. I will see if I can find
the magazine and get back to you.

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RE: OS91FX dies in flight - 5/20/2012 4:20 AM   
oldtyme


 

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quote:

ORIGINAL: WRM

IT is vapor locking . All the FXs do it . That is the reason OS moved the needle valve to the carburetor . There was an article in Model Airplane News a couple of years ago. I will see if I can find
the magazine and get back to you.

WRM............I distinctly said very early on that I was aware of the vapor locking problem and had resolved it with the help of OS. All FX's do not have this problem...........as the tech from OS stated......this problem manifested itself in the 91FX. I have had 25, 46, 61 and 91 FX's and the only problem I have ever had is with the 91, none of the others are/were a problem and now the 91....with the fix.....is not a problem either. The fix is a new backplate w/o the needle mounting on it, a new mounting bracket and a new fiber needle valve housing and new needle valve (same as used on the OSLA65). Until I ran into the old fuel thing it was running without a hitch.

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RE: OS91FX dies in flight - 5/20/2012 4:46 AM   
WRM


 

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