RE: OS 91 FX problem
 

hi
contact TOWER HOBBIES-OS has issued new parts for the engine for FREE-(thus recognizing a defect in design )-a remote needle valve and a new back plate-i spent two months trying to get this engine to run as it should the new parts solved the problem i run a 13/6 APC on my 60 ULTASPORT-OS WILL also redo you engines internals if they were damaged -mine were not REGARDS TONY

RE: OS 91 FX problem
 

An email is sent to tower hobbies, but I dont think this will help

They dont sell the engine anymore and it is bought in Norway

But it is worth a little try :)


I found this : http://www3.towerhobbies.com/cgi-bin...XMW56&P=PU. In the middle of this site its written a comment about os 91 fx, and what that is needed ifI buya newneedle valve assembly(backplate and bracket)

I guess its this I eventually need.If I dont get it free, I guess Ill try to cut off the needle valv eassembly first, and mount it on the front of the fuselage

RE: OS 91 FX problem
 

I had several of the early versions of the .91FX. You will find that the problem to be on the needle valve house, there is a silver hex bolt that bolts into it to plug a hole. The "O-rings" that OS used are too soft, and they need to be replaced. The glow fuel desolves these "O-rings". These "O-rings" allow air to leak into the needle valve control unit. There is also two of the fuel nipples that have the same "O-rings" I used to use Plumbers white teflon tape to wrap the threads, and this would solve the issue for 50 flights. On the "Hex nut" you will see one or two little holes drilled side ways into the threaded bolt. Make sure these are not covered with the teflon tape,or you will cut the fuel off. Of course, if you don't want to go through these hassles, buy a new needle valve assembly.

RE: OS 91 FX problem
 

Ive thought that thishex bolt may be a possible reason many times

I unscrewed it now, and it wasnt any "O-ring" there.

Im gonna order new needle valve assembly anyway :)

RE: OS 91 FX problem
 

While you are waiting on the new valve assembly, try the teflon tape. Doesn't cost you anything, if you have some in the garage. If not, shouldn't be more then a $1 at the hardware. Also, if you are using a tuned pipe, use an OS -A-5 plug. It is a colder running plug for the higher RPM's and temperature.

RE: OS 91 FX problem
 

The flying season hasnt begun yet, so Ill wait :)

Here in Norway, its winther with snow and cold weather.

I have begun to do my planes ready for the flying season now, so a bit waiting for the needle valve assembly is ok</p>

RE: OS 91 FX problem
 

Look at the other Forum on the Home page of RCU labeled "Big MayDay". There are some other guys up in your neck of the world that are flying jets off of ice.........crazy to me........lol.

RE: OS 91 FX problem
 

I saw the "canadian style"-video, cool!

RE: OS 91 FX problem
 

HI
DO SEARCH THE FORUMS here for much more info on the 91 FX probleman easy quick fix is to cut you present needle valve off of the back plate and mount it somewerethis does look like an air leak problembut in my opinion it is not-it is a heat transfer problemDO NOT LET TOWER OFF THE HOOKthe problem with the engine is with the earlier engines-so it does not matter if they are still selling them-i have one of the first engines and the new parts solved my problems it did take me 2-3 months of some difficult days at the fieldto get the engine running excellent-i was getting air bubbles in the fuel line to the carb and needle valve -ONLY AT MIDRANGE from day one-but no internal damage thank goodness i think the engine comes up a bit short on power for its sizeturns a 13/6 APC -my OS 1.08 FSR will blow its doors off15/6 APC as will my 75 AX 14/6 APC BEST REGARDS TONY

RE: OS 91 FX problem
 

Ive been searching this forum and other forums for problems with OS 91 FX, the reasonis probablyheat transfer or air leak. If I order a new needle valve assembly, that will solve both thatalternatives

Ive had problems with my firstOS 91 FX in many years, therefore it will be best to choose the "safest" way to solve it :)

Its time enough also

RE: OS 91 FX problem
 

Hi, have you checked your clunk tubing? Sometimes a pin hole can cause erratic malfunctioning.
Regards
Juan

RE: OS 91 FX problem
 

I worked with the tank and fuel lines many times, so a hole like that, I should have disappeared :)

Anyway, the plane is crashed and gone, so its impossible to check</p>

RE: OS 91 FX problem
 

Maybe a perry pump also will help :)

Never used a pump in my planes, but that will maybe be a nice solution, not in just my case, butin many other casesif an engine isnt running as it should.

If I also order a perry pump which use the pressure power, do I need other products, like a check valve?

I guess a perry pump will be a great solution since I have a smaller pitts muffler, which probably dont makes very much pressure

RE: OS 91 FX problem
 

No check valve or muffler pressure needed.

RE: OS 91 FX problem
 

It should run without a pump.

A pump would probably be masking, and/or compounding the original problem at this point.

RE: OS 91 FX problem
 

Off course, I will try to get the engine run well without a pump first, I hope and guess that will be easy with the new needle valve assembly.

But I will also buy a perry pump and have it as a "back up" :)

Its possible to buy a new backplate for the 91 sx to mount on the 91 fx, without the needle valve assembly, but that isnt necessary. As written earlier in this thread , cutting of the needle valve assembly and use the original backplateis a good solution.

RE: OS 91 FX problem
 

Just got the replacement needle valve and the bracket indirectly from Tower Hobbies. Now its just to find time to assemble it and try to run the engine :)