loughbd

OK you guys, here's one for you. I have an OS 120 Surpass that I made from parts from several different engines. I have it mounted on an old Dragon Lady I've been dragging around for 15 years. This thing is the one engine that is kicking my bu--. It runs great. hauls the plane around with no effort but it has one little bitty problem. The needle has almost no effect. Back it out about three turns, prime , flip the prop and whamo, off it goes. Move lean it or richen, nothing. It will quit if you lean it too far but you can open the needle all the way to the point it falls out and nothing happens. I have used bigger tubing, changed pumps, changed carbs, used no pump, used a perry oscillating pump, nothing. Good compression, actually everything is good but it won't richen up. No intake leaks, new plugs. new fuel, etc.

Anyone got any ideas

Actually solved the airplane problem, I put a YS120NC on it. Fit in the same mount as the OS

pe reivers

You may have a (dirt?) restricted needle housing or fuel trajectory from tank to engine that limits the max fuel flow.

Iflyglow

My Feedback: (79)

Loughbd,
I see you fixed the problem.

pe reivers

I don't see the point, where he resolved it?
I once got a carb back that was "no good" and it was sent back because it could not be adjusted well.
You would not believe the amount of crap I extracted from the fuel jet bar. I must have a picture somewhere, but only will dig it up when someone is interested.

w8ye

My Feedback: (16)

If the idle needle is screwed in too far, the HS will be less effective.

Iflyglow

My Feedback: (79)

Preivers,
Read the whole thread!

I put a YS120NC on it. Fit in the same mount as the OS s the YS 120NC which fit the mont perfectly.

Flyboy Dave

My Feedback: (21)

It had the wrong needle in it. That's why it could never be richened up
no matter what you did to it. Or the needle wasn't made correctly, too fat.

FBD.

loughbd

That was the very first thing I or anyone checks. I also used three different carbs and changed the needle valves and used each one in each different carb. Did all the obvious carb things and tank things. It does the same thing on the bench so it isn't the plane or tank. The YS runs fine on the same set up.

loughbd

Yup, the dragon lady goes straight up with the YS and the needle valve is more than an ornament.

Big Bopper

THe nozzle may have been defective or the fuel inlet restricted.

Harry Lagman

How was your cam timing? Was the engine performing at full throttle as you'd expect?

loughbd

Like I said, I use three different carbs. Not all would have plugged fuel inlet. What is a "nozzle"?

loughbd

Cam timing is right on the money. Engine runs fine , just can't richen the mixture with the needle valve. What's weird is the setting seems to be perfect where it is. Sort of like the factory set beginner's engines

loughbd

Nope, all three carbs have the right needle valve.

Flyboy Dave

My Feedback: (21)

Is the fuel inlet drilled incorrectly like on this carb ? These ran OK
but would lean out in flight, because you could not get a rich enough
adjustment.

FBD.

loughbd

That isn't an OS carb and I used three different carbs. Yes I checked to see if there were any obstructions. No there weren't.

Motorbrain

Put a Magnum carb on it. The OS parts cost too much.

loughbd

I'm trying to make it WORK. I'm sure not going to put a second rate carb on it. Plus the fact Magnum doesn't make a carb like the pumped OS120 Surpass uses. Not even close.

mig3

The problem is is the LOW NEEDLE is too far open! NOT closed! That is a large engine he is talking about and the suction is very strong! Once he closes the high all the way she shuts down! That means the high needle IS seating in the seat completely because if it was not, then the engine would still run on. If the LOW is too far open, then as he closes the high, pressure changes (suction) in the carb and the fact that the low is to far OUT of the spraybar allows the fuel to get into the engine as there is NO pressure against the high fuel flow then fuel continues to flow from the WRONG LOW ADJUSTMENT rather than the high at this point untill he closes the high all the way cutting the fuel off to the engine all the way untill she quits! This is a minor adjustment. BOTH needles have to be "MOVED OVER" so to speak. Open the carb and look inside the ventury at the spraybar. WHERE is the end of that LOW needle sitting? Can it even be seen? OR is she too far out? Try that, it may work for him since many parts were taken apart and PERHAPS removing the high altogether then closing the low needle ALL THE WAY and THEN opening it 4 full turns and re-inserting the high till seated then opening IT 2 and 1/2 turns to get the Surpass running may be a VERY close place to begin to balance both needles positions!

GOOD LUCK!
MIG3

speedster 1919

My Feedback: (3)

Mig3 He said he had 3 different carbs on it , but I agree with you. If each carb got pre set ,most guys reset each one the same way. Tuning habits are hard to break and the timing could be off one tooth. The secret is in the LOW NEEDLE.

Super Splatter

New question:

I have a Surpass I 120 pumped with very little time on it. the one OS recalled

I have it on a GP GeeBee.

I did the trick with hooking a "T" to the line from the pump to the carb and return it to the return line.

spent some time and got good idle, good throttle response and since it's a pump I kinda have it needled near the edge.

Runs excellent. The only prop I tried wasa 16-6 APC and peaked at 9100 RPM, backed it down to 8900. Seems all good.

the question... What prop to run on a GeeBee. The RCU review for a GeeBee & a OS120 was 15-7 APC. Any ideas?

What RPM should I shoot for.

Super Splatter

Big bump for my question , please

loughbd

Does anyone here have ANY idea what Miggy3 is talking about?? He obviously didn't read what my problem is. It runs fine, It will shut down if you screw the needle in all the way. It works fine in every sense except you can not richen the mixture by opening the main needle. This has NOTHING to do with the idle. It's not even at an idle. Also there is no low needle per se. It has the little U shaped gizmo that moves about 15 degrees in either direction that moves an eccentric that moves the idle adjust in and out.. I started with it in the middle as per the instuction sheet. The idle was fine, just a bit rich as it should be. At full throttle the idle has almost zero effect on the way the engine runs.

The needle valves, both hi and lo, have nothing to do with suction. That is based on the ability of the piston to draw a vacuum on the cylinder and the size of the opening in the VENTURI and assuming there are no leaks in the intake passages.

It's actually not all that large an engine either. Saito is making up to 3.25 and OS makes up to 3.2 cid four cycles.

loughbd

The low needle has no effect when the throttle is wide open. The barrel moves in and out when the throttle is moved and this moves the low end needle in and out of the spray bar changing the mixture. At full thorottle the idle needle is completely out of the spray bar opening and has no effect. This is on a regular two needle carb. In an airbleed carb the hole is completely covered by the rotating barrel and has no effect at wide open throttle.

One other little item. The FIRST thing I do whenever having problems with an engine is to CHECK THE INSTRUCTIONS. I own 100's of engines but I still believe the manufacturer knows at LEAST as much as I do in making them work. We had a saying in the Navy. When all else fails, read the instructions.

Here's another little fact someone should tell Miggy. The c12 and c13 carbs on an OS120 Surpass DO NOT have the rotating barrel that moves in and out and does not have a conventional spray bar. There is NO spray bar. These carbs have a flat butterfly valve that controls the airflow, not a rotating barrel. There is no low end needle either. The C12 has the regulator on the pump and the C13 has the regulator on the carb. There is no way to turn the low needle (that doesn't exist) three or four turns. The low end adjust has a small U shaped Arm the fits in an eccentric screw. When you turn the screw it moves the U shaped "do da" left ot right. It can only move about 10 degrees in either direction. NO WAY it will move four turns.

If Miggy is going to give advice on how to solve a carb problem, he at least should know how that carb works.

I actually got the engine to work. The problem was very simple. There are three very small o-rings in the regulator. One had hardened and broken. I replaced it and the engine seems to work fine. However, I see no reason to take the YS 120NC off. The plane is a rocket with it and I'm satisfied.

It was Baxter that turned me on to the regulator. Bax , I took it apart and it still works.

hockeypilot

My Feedback: (4)

New question regarding the OS120 Surpass I just bought with a plane;
What is the "nipple" at the bottom of the crankcase on the output shaft case?
It looks like a pressure port of some kind.
When the engine runs, it runs great but is new enough it hasn't broken in yet.
So, should I be feeding that port into the tank for additional fuel pressure?