Help! issues with my .91 fx cutting out after running for a minute!!

[bigdogsummit800]

I have a .91 fx installed on a aerowroks edge 540 60inch wingspan exactly according to the directions. Having a problem keeping the engine running. I shortened the fuel line as much as i could, double checked that the clunk in the tank was set up correclty. Changed glow plugs. The fuel is getting to the carb fine, motor starts up well with no bubbles in the fuel line. Throttle up to adjust the high end and like 3 secends after the motor just shuts off completly. pulled the full line off from the remote needle valve to the carb and the line is bone dry. pulled the line off from tank to the remote needle valve and its 100% full of fuel. When starting up we can see the fuel flowin to the carb with no bubbles. The motor does not seem to be overheating. I have been trying to get it to stay running with out the cowl and keeping it rich. But after running for a minute or so the line will just go completly empty and the engine will quite. Please Help!!! im dying to fly this airplane!!

[DAGONZ]

Are you re-fueling after it shuts down?

[wesryman]

If your line from the Remote to the Carb is dry but the line from the tank to the remote is full then the fuel is not making it thru the needle valve, try unscrewing the needle valve until you can take it out then flush out the remote with fuel from either one of the fuel fittings. It sounds like you have a restriction in the remote, either that or you are turning the needle in so far that no fuel can get thru.

[bigdogsummit800]

Thanks for the responses guys. No I haven't been refueling it. And we thought about restrictions in the needle valve and took it out 3 different times blowing the fuel out of it thinking maybe there was some junk in there or soemthing. None of that changed the symtoms. We started with the needle valve 2 and 1/2 turns out just like the book recomends. Remeber it runs good for a minute or so before it will stop pulling fuel. It runs long enough to tune the high end. We tuned it so it was a tick rich.

[gpenner]

I know you're talking about fuel, but looking at the title line, I would have said some of the head bolts are lose. That's what my heli was doing as well as a friends .91 fx.

As for fuel issues, I had my clunk come loose on my 40% Edge on Tuesday. Found out just after take off. Had just enough airspeed to bring it around.

[DAGONZ]

Does the .91FX have the plastic fuel nipples at the carb and remote? I have seen were the plastic is cracked on other OS engines and causes problems. One in particular it would draw fuel to prime and start but soon die. Noticed if after it was primed the fuel would draw back out of the line between the carb and remote. Just some thing else to check. Hope you get the fly that awsome bird soon.

[imacflyr3]

Sounds like possibly a problem with the tank pressure line from the muffler.

[bigdogsummit800]

	Quote: Originally Posted by DAGONZ
	Does the .91FX have the plastic fuel nipples at the carb and remote? I have seen were the plastic is cracked on other OS engines and causes problems. One in particular it would draw fuel to prime and start but soon die. Noticed if after it was primed the fuel would draw back out of the line between the carb and remote. Just some thing else to check. Hope you get the fly that awsome bird soon.

The symptom described is pretty much exactly what is happening, but I am pretty sure mine doesn't have the plastic fuel nipples.

[AJPOPO]

IM not a pro but maybe if u tried leaving ur glow starter on the glow plug while u run it up. u say u enriched and enriched maybe the fuel put the plug out. ( if u do get it working that baby is gonna HAUL! ) Good Luck you will need it...

[The Hobbyman]

I have had this problem with this same engine before, I found the engine was over compressed, try putting an extra headshim in it and drop you're nitro content to 5%, mine actually blew a couple of plugs out in flight. It runs ok now but still the head bolts come loose every now and then, if it is inverted use a OS F plug.

[TONY0707]

hi you seem to be running on the fuel in the crankcase---my 91FX needle valve is out 5 1/2 turns on the top end--you may need to let more fuel into the engine to keep it running--do open the low end nv also-as starting is usually effected by the low end more than the top end--i often will hook up a fuel line to a carb-and blow into it to be sure the engine is getting fuel--you can hear the air-slightly with the carb almost closed and a lot with the carb open-just gives you a ball park kind of a setting to get the engine to run--might sound silly-but had the same problem--when my fuel line and pressure line were reversed by mistake just recently--let us know how you do so other may benefit ENJOY REGARDS TONY

[BobPhx]

Make sure the line from the carb to the needle valve is the tiny stuff. The stock OS line has a very small ID. I once replaced the stock line with normal "medium" silicon line (fit over the nipples fine) and had nothing but trouble. Switched to "small" silicon line (like you'd use on an .049), problem solved.

Bob

[wylieruneyjr]

Your too lean if ya running out of fuel between the remote needle and carb. Or you have some fuel obstruction either at the needle or fuel line itself. Or you are drawing a airleak , pinhole in between the remote and carb. Try probing a needle or stick pin into the pressure fitting on muffler to be sure its clear. Check that the fuel clunk in your tank has not been thrown foward due a hard landing. try very rich needle settings on both the idle and speed needle. GOOD LUCK
O and make sure your not connecting the tank vent line to the remote needle valve.

[TONY0707]

hi just remembered -were the tank ---clunk line --comes into the needle valve--you will see a circular fitting--disassemble it-as i found some dabri in that fitting-and i always run a clear fuel filter before the needle valve on all my planes --and do suggest you do the same---this allows you to observe any debri in the fuel lines---before it gets into the carb and starts to give you problems with the engine running-or worse a dead stick--the circular fitting i am refereing to is a fuel feed to the needle valve-is odd to this engines design--and the rear nv design-(which i do not like )-i found some dirt in mine --could be preventing a full stream of full to be flowing- so you are just getting enough fuel to run some--but not enough to keep you running
i am also going to suggest that you strain every gallon of glo fuel you buy--i use a small mesh metal kitchen strainner--you would be very surprised the amount of fuzzy material i have found in the strainner very often with a new gallon of glo fuel
use double tubing on all your tubing fitting joints-keeping the pressure and fuel line as short as is possible as glo engines basicly work on a vacuum draw principal-with some help from tank pressure
i do not agree with the person who said to go to a small fuel line between the nv and the carb-these bigger engines need there fuel delivery-as i run standard size fuel line myself on this engine in that place with no problem
i am running a 13/7 APC at 12,100 RPMS for some time now--just be sure you are not trying to turn to much prop as that leads to a good many running problems--do get back and let us know the solution to your engine problem -so we all may benefit--- handling a 91 FX for 8-10 years---ENJOY REGARDS TONY

[2walla]

The needle valves on the os91fx are known to leak air.. You are getting a harmonic frequency and the thing is sucking air and leaning out. Try changing prop size, prop balancing, Or a different remote needle valve.