OS FS120 Surpass I with pump
08-27-2004, 08:50 AM
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OS FS120 Surpass I with pump
I have an old 120 surpass that runs very well (once I found out how to tune it). The problem is that the needle valve adjustment range is very narrow. One click or less.
I have heard that there is a needle valve assembly available for this engine that has a gentler taper which will widen the tuning range, but have been unable to find part numbers, ordering information, or even where I can go to get information on it.
If anyone knows where I can get one of these needle valves assemblies I would really appreciate you passing the info along to me.
Thanks,
doubledee
I have heard that there is a needle valve assembly available for this engine that has a gentler taper which will widen the tuning range, but have been unable to find part numbers, ordering information, or even where I can go to get information on it.
If anyone knows where I can get one of these needle valves assemblies I would really appreciate you passing the info along to me.
Thanks,
doubledee
08-29-2004, 10:03 AM
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RE: OS FS120 Surpass I with pump
David:
From your email to me:
With the needle this sensitive there are two more likely possibilities.
One is damage to the needle or seat, from turning it shut too tightly. Usually the correct mixture spot will still be close to the original number of turns open. This can also be caused by having a needle extension with no support, the vibration causes the needle to hammer the seat.
The other is specific to pumped engines, the needle setting will be sometimes as little as 1/2 turn open. This is caused by the fuel pressure being set too high.
In the case of damage, usually the spray bar has to be replaced, the needle itself is seldom hurt.
Set the fuel pressure for the engine to be blubbery rich about 3 1/2 turns open on the high speed needle (be sure the idle needle is set rich when you do this) with the peak rpm 2 1/2 ti 2 3/4 turns open.
All this is assuming you have checked carefully and eliminated any air leaks between the carb and the cylinder head.
Maybe Bax will come in here, he knows the OS engines a lot better than I.
Bill.
From your email to me:
...the needle valve adjustment is very, very sensitive. 1 click will cause abut a 400-500 rpm shift.
One is damage to the needle or seat, from turning it shut too tightly. Usually the correct mixture spot will still be close to the original number of turns open. This can also be caused by having a needle extension with no support, the vibration causes the needle to hammer the seat.
The other is specific to pumped engines, the needle setting will be sometimes as little as 1/2 turn open. This is caused by the fuel pressure being set too high.
In the case of damage, usually the spray bar has to be replaced, the needle itself is seldom hurt.
Set the fuel pressure for the engine to be blubbery rich about 3 1/2 turns open on the high speed needle (be sure the idle needle is set rich when you do this) with the peak rpm 2 1/2 ti 2 3/4 turns open.
All this is assuming you have checked carefully and eliminated any air leaks between the carb and the cylinder head.
Maybe Bax will come in here, he knows the OS engines a lot better than I.
Bill.
09-01-2004, 07:36 AM
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RE: OS FS120 Surpass I with pump
William and Bax,
Appreciate the info. I put it on a test stand and managed to get it close then installed it in the airplane and took it to the flying field where I fine tuned the upper end. It is turning 10,500 with a 16X4W APC prop. The high end setting is extremely narrow, 1 to 2 clicks, so I am going to order the needle valve Bax suggested and see if I can't tune it even finer. Runs good, though and I still have to get the low end right.
Thanks again,
doubledee
Appreciate the info. I put it on a test stand and managed to get it close then installed it in the airplane and took it to the flying field where I fine tuned the upper end. It is turning 10,500 with a 16X4W APC prop. The high end setting is extremely narrow, 1 to 2 clicks, so I am going to order the needle valve Bax suggested and see if I can't tune it even finer. Runs good, though and I still have to get the low end right.
Thanks again,
doubledee
09-02-2004, 01:29 AM
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RE: OS FS120 Surpass I with pump
Hi Guys,
I have this engine in TF Bonanza and it behaved very well untill unce while refuelling I fergot
to remove the tank vent stopper causing the everpressure and tank to swell to level of almost
bursting. Since then the engine never runs smoothly at high end irrespective of NV settings.
Can the pump be damaged by overpressure ?.
Thanks
I have this engine in TF Bonanza and it behaved very well untill unce while refuelling I fergot
to remove the tank vent stopper causing the everpressure and tank to swell to level of almost
bursting. Since then the engine never runs smoothly at high end irrespective of NV settings.
Can the pump be damaged by overpressure ?.
Thanks
