O.S 120 FS pre Surpass
09-06-2009, 02:13 PM
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O.S 120 FS pre Surpass
hi Bax
I received an old O.S 120 FS from the first series.
The engine was few times run, and then stored for about 20 years.
I put it in a plane that I repaired and after a couple of flicks the engine started.
I used at begining 10% nitro fuel, with 15% Molsyn 150k oil and 3% castor (homebrew). graupner 15x8 prop.
Engine puts out good power...but I couldn't get it to tune right at idle and transition. I noticed some detonation then changed to 5% nitro fuel...knocking went away. But the problem at idle and at midrange stills there
The problem is....I start the engine...bring it to full power, set the max rpm and then a couple of clicks as usuall, then I start with the idle...at the begining idle seems lean...high idle with a quite closed carb barrel, transition sags a little....but if I let it idle for about 10-15 seconds, the engine loads up too much, to a point where it barely runs and eventually quits... so I lean it a little...but it will just not run at all...or die at the transition...so it means It cannot be further leaned out (it will eventually detonate a couple of times when I put the stick back). I can only set a very high idle, there the engine works barely acceptable..but it's too high to land... last time I had to abort the landing...throttle up and the engine died...engine mount damaged.
I'm planning to dismantle the engine and take a look at everything... I can't find where is the problem with the engine..I've made very slight adjustments at a time...but I can't get the engine tuned? There was any known issue with the carb? Engine is installed inverted, but I turned the plane and the engine behaves the same...first lean and then too rich,
Engine puts out good power at full throttle...about 8400 with the prop mentioned.
I would appreciate any help you could give me.
Thank you
Jorge
I received an old O.S 120 FS from the first series.
The engine was few times run, and then stored for about 20 years.
I put it in a plane that I repaired and after a couple of flicks the engine started.
I used at begining 10% nitro fuel, with 15% Molsyn 150k oil and 3% castor (homebrew). graupner 15x8 prop.
Engine puts out good power...but I couldn't get it to tune right at idle and transition. I noticed some detonation then changed to 5% nitro fuel...knocking went away. But the problem at idle and at midrange stills there
The problem is....I start the engine...bring it to full power, set the max rpm and then a couple of clicks as usuall, then I start with the idle...at the begining idle seems lean...high idle with a quite closed carb barrel, transition sags a little....but if I let it idle for about 10-15 seconds, the engine loads up too much, to a point where it barely runs and eventually quits... so I lean it a little...but it will just not run at all...or die at the transition...so it means It cannot be further leaned out (it will eventually detonate a couple of times when I put the stick back). I can only set a very high idle, there the engine works barely acceptable..but it's too high to land... last time I had to abort the landing...throttle up and the engine died...engine mount damaged.
I'm planning to dismantle the engine and take a look at everything... I can't find where is the problem with the engine..I've made very slight adjustments at a time...but I can't get the engine tuned? There was any known issue with the carb? Engine is installed inverted, but I turned the plane and the engine behaves the same...first lean and then too rich,
Engine puts out good power at full throttle...about 8400 with the prop mentioned.
I would appreciate any help you could give me.
Thank you
Jorge
09-08-2009, 09:23 AM
#2
My Feedback: (11)
RE: O.S 120 FS pre Surpass
8400 RPM is low. We usually see about 1,000 RPM more with an APC 15 x 8 propeller. You can easily turn near 10K with a Zinger 15 x 8 propeller.
Your O.S. Max engine with pump should be set up in a slightly different manner than a non-pumped engine. Most modelers tend to get them set with the mixture too rich.
One sign your engine's not adjusted correctly would be surging at full throttle. This almost always means it's too rich. Also, the idle may be too rich no matter what you do to the idle mixture. If the idle is leaned a lot, but it's still too rich, the high-speed needle's too rich and needs to be properly set.
To get a good setting, you need to use a tachometer. Once the engine's had enough running to accept being leaned to peak RPM, use the tachometer to lean the engine to its peak.
At full throttle, lean the engine until the RPM stops increasing. Continue to lean the engine to the first sign of RPM drop or detonation. When you get to that point, richen to the point just before you had the RPM drop or detonation and leave the needle there. DO NOT lean to peak and then richen your usual 1/4-1/2 turn.
With a good-quality fuel, the pump system will insure that the engine receives enough fuel. The regulator in the system will make sure that the mixture stays correct as you change the throttle positions. Fly the engine to see how the mixture may change as the engine unloads in the air. You may have to lean or richen slightly, depending upon how it acts. Once you've found the proper setting, you should note the change from the absolute maximum lean position. Now you have a repeatable setting for your engine.
Newer O.S. engines with pumps have a broader range for the needle setting, but you can use the same method for all of them.
If you cannot get a good setting, you may have problems in the pump unit, which also has the regulator. If so, then you'll have to try to locate a new one. They usually cannot be repaired, and the factory no longer provides support for the original FS-120 Surpass engines.
Your O.S. Max engine with pump should be set up in a slightly different manner than a non-pumped engine. Most modelers tend to get them set with the mixture too rich.
One sign your engine's not adjusted correctly would be surging at full throttle. This almost always means it's too rich. Also, the idle may be too rich no matter what you do to the idle mixture. If the idle is leaned a lot, but it's still too rich, the high-speed needle's too rich and needs to be properly set.
To get a good setting, you need to use a tachometer. Once the engine's had enough running to accept being leaned to peak RPM, use the tachometer to lean the engine to its peak.
At full throttle, lean the engine until the RPM stops increasing. Continue to lean the engine to the first sign of RPM drop or detonation. When you get to that point, richen to the point just before you had the RPM drop or detonation and leave the needle there. DO NOT lean to peak and then richen your usual 1/4-1/2 turn.
With a good-quality fuel, the pump system will insure that the engine receives enough fuel. The regulator in the system will make sure that the mixture stays correct as you change the throttle positions. Fly the engine to see how the mixture may change as the engine unloads in the air. You may have to lean or richen slightly, depending upon how it acts. Once you've found the proper setting, you should note the change from the absolute maximum lean position. Now you have a repeatable setting for your engine.
Newer O.S. engines with pumps have a broader range for the needle setting, but you can use the same method for all of them.
If you cannot get a good setting, you may have problems in the pump unit, which also has the regulator. If so, then you'll have to try to locate a new one. They usually cannot be repaired, and the factory no longer provides support for the original FS-120 Surpass engines.
09-08-2009, 09:58 AM
#3
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RE: O.S 120 FS pre Surpass
Hi bax, thanks for the reply
My engine doesn't have any pump, with a normal carb. The engine is a PRE SURPASS...the one with two valve covers...
Anyway thanks for the info.
Jorge
My engine doesn't have any pump, with a normal carb. The engine is a PRE SURPASS...the one with two valve covers...
Anyway thanks for the info.
Jorge
09-09-2009, 09:25 AM
#4
My Feedback: (11)
RE: O.S 120 FS pre Surpass
OK, we thought it was the original FS-120 Surpass I. 8,400 RPM is good for the original FS-120 engine. If you canot get a good setting of the carburetor, even when the engine is running in the upright position, it may be that the compression is starting to become too low. As engines get worn out, the compression starts to go away, and proplems with idle and throttle transition are the first indications that there's a problem.
You may also want to try a fuel with less oil. The four-stroke engines will run very nicely on fuel with 14%-15% oil content. 5%-10% nitro is plenty for that engine.
You may also want to try a fuel with less oil. The four-stroke engines will run very nicely on fuel with 14%-15% oil content. 5%-10% nitro is plenty for that engine.
