OS 50 Ring Fuel Delivery Problem
 

I'm bench running a 50 size engine with rings.

The fuel lines and tank was leak checked before mounting the engine by blowing into the vent line on the tank and pinching off the line at the carburator.

The fuel lines and tank was leak checked again after the bench run by blowing into the vent line on the tank and immersing the tank, fuel lines and remote needle valve assembly in water and pinching off the line at the carburator. This test was repeated this time by blowing into the line at the carburator and pinching off the vent line at the tank while immersing the tank, fuel lines and remote needle valve assembly in water. No leaks were found.

The fuel line between the remote needle valve and carburator exhibits a continuous stream of bubbles. Bubbles are continuous no matter how I hold the tank, above the carburator, level with the carburator or below the carburator. Obviously, vibration is not affecting the fuel in the tank because I'm holding the tank.

The fuel line between the tank and remote needle valve does not have bubbles.

Engine runs only if it is fuel rich and four cycling. If I begin to lean it out the engine runs but at any moment it will suddenly die lean.

The needle valve o-ring was replaced even though the previous o-ring was not damaged and did not leak.

Engine has not been in a crash.

Engine has very little time on it. It was broken in with two tanks of fuel while mounted on an Eagle 2. It was flown 6-8 flights running very rich (four cycling) without a problem. When I begin to lean the engine it dies before it ever reaches peak RPM. It's not possible to hold peak RPM and richen the mixture. Engine dies before the adjustment is completed.

Fuel is CoolPower 15 percent.

I disassembled and inspected the remote needle assembly before bench running the engine. I checked all the seals, fuel nipples, examined sealing surfaces under a magnifying glass and reassembled. No problems were found.

What shall I do to fix it?

Doug

RE: OS 50 Ring Fuel Delivery Problem
 

You don't say what propeller and fuel you're using. If you have a too-large propeller, then that could cause difficulties. If your fuel is old, that could cause difficulties.

We'd use a 10 x 7 or 8 propeller or even an 11 x 7 or 8 prop. Nothing larger because you want the engine to turn up. It should turn over 12,000 RPM when leaned to just rich of peak RPM on the ground. Make sure you have fresh fuel with at least 18% oil content. We'd normally use 10% niro, but 0%-15% is OK.

You may need to check for some kind of leak/obstruction or such in the fuel system. If the engine's tending to die when you try to lean it, then you most certainly have a fuel draw problem. Are you using the stock muffler?

2 tanks of fuel will never "break in" an engine. That may give you enough running time to allow you to fly it, but the engine will "come in" over the next gallon of fuel or so. We usually don't fly an engine until we have 45 min. to an hour of running on the bench, but that's just our way.

You need to go over everything carefully. The O.S. Max .50 SX is one of the easiest engines to set up and tune. We'd not know why your's has the difficulty it does.

One thing to consider: if the engine tends to die when you try to lean it, and it's in the model, you're likely getting vibration-induced fuel foaming. That's when air is agitated into the fuel in the tank while the engine's running. You won't likely see the air in the line to the needle because it's in the form of micro-bubbles. They will congregate at the needle and then break off as visible bubbles. That makes leaning a problem. Many modern models have lightweight airframes that just cannot absorb vibration, and they also have very little room for proper fuel-tank isolation. Ideally, you should have one inch of foam rubber around the fuel tank to keep it from getting influenced by the engine's vibration.

RE: OS 50 Ring Fuel Delivery Problem
 

The propeller is a 10x6 to keep the engine lightly loaded until fully broken in.

Fuel is CoolPower 15% and yes, it is fresh.

Yes, I'm using a stock muffler. All engine parts are stock.

There are no leaks. The original post carefully details the double testing, and immersion testing that has been done.

Based on your reply, I checked for obstructions. With the needle valve open, I can easily blow air into the vent line at the muffler. There are no obstructions.

The engine is not in a model. I'm bench running it. I'm holding the tank to eliminate fuel foaming as the cause. I'm also holding the tank because I wanted to find out if fuel level with respect to the carburator is a problem.

Muffler is pressurizing the tank.

This engine has not been run to 12,000. Bubbles after the remote needle valve appear to be larger and obviously are flowing faster as RPM increases. Engine dies before it reaches 12,000.

What shall I do to fix it?

Doug

RE: OS 50 Ring Fuel Delivery Problem
 

I broke in a new OS 40 LA over the weekend that has a Plastic remote needle valve assembly. I used the same fuel and propeller I had on the 50 ring. I used the fuel tank, fuel hose and bench mount for the engine. Everything is the same except the engine itself.

The OS 40 does not have bubbles in the fuel after the remote needle valve.

Evidently, the problem is in the metal housing of the 50 FX remote needle valve.

What does OS have to fix it? Doug

RE: OS 50 Ring Fuel Delivery Problem
 

bubbles in the line between a remote needle and the carburetor can be caused by leakage in the needle assembly, but can also be caused by air in the fuel before it reaches the needle. The needle has a stagnation point and micro-bubbles can 'stick' there and form larger ones, which you see.

If you replace the needle assembly and still get bubbles, then you'll have to examine the fuel system to see if you have an air leak of some kind previous to the needle.

If you have high fuel pressure, then you would not get air leaking into the fuel system at the needle. If there's potential for a leak, fuel would exit the needle assembly instead of air being sucked in...due to fuel pressure.

We'd try a new needle assembly, first.

Your difficulty is not something that is at all common with the O.S. .50 SX engine.

RE: OS 50 Ring Fuel Delivery Problem
 

I was very careful to leak check before and after the bench run.

I'll send the engine in for repair under warranty.

Doug