OS FS-91S needle setting
 

I have a low time FS91 Surpass that will only peak at very close to a fully closed needle setting,no more than 1/4 turn open and it will in fact run with the needle fully closed.
This condition has been slowly getting worse over time and the engine now wont develop enough power to take the model off,and regularly quits in the air.
Does the mixture control setting have an effect on where the needle must be set for full power reliable running.?
The bearings have been checked ,ditto the valve clearance,and the engine has very good compression.?
What else could be wrong.?
If the problem is the seat or the needle can these be replaced as opposed to buying a new carb?
If it is the mixture needle that needs to be reset ,how do I do this,and how can the needle get this far out of tune on its own?
Thanks very much...............Kevin

RE: OS FS-91S needle setting
 

If the idle mixture setting is turned in a lot, then the high-speed needle will tend to be well open. However, if the idle needle's turned out a lot, then the high-speed needle will usually be at 1-3/4 to 1-1/2 turns out from closed when leaned to just rich of peak RPM. If the needle must be turned in a LOT, as your's is, then it's likely you have damage to the needle and the needle seat in the carburetor. This can be confirmed by removing the needle and looking at the pointy part. You'll see a polished ring around it. That means that it's been beating against the needle seat due to vibration. You'll need a new carburetor body and a new needle to make a fix.

RE: OS FS-91S needle setting
 

Thanks Bax.........is the carb body for this engine still available and the needle valve too?

Kevin

RE: OS FS-91S needle setting
 

The carb and carb body have been discontinued, but the needle is still available. Please remember that this engine went out of production a decade ago.

RE: OS FS-91S needle setting
 

Is their any other solution in my FS92 happens the same runs only when needle is fully cloused and performance drops at high speed.
Pravin

RE: OS FS-91S needle setting
 

The needle seat in your engine's carburetor body is damaged. You'll need to obtain a new carburetor body.

RE: OS FS-91S needle setting
 

Thanks iwill order for new one. Also pl. advise can asp 91fs carb can be fitted in os 91fs?

RE: OS FS-91S needle setting
 

We only know O.S. parts. We cannot comment on non-O.S. parts because we're not familiar with them.