OS 70 Ultimate problems
 

I have just bought an OS 70 Ultimate engine and mounted it in a 40 size Sukhoi. I'm running the engine on 15% nitro and 15% synthetic oil. The engine is extremely easy to start an idles well but I have a big problem with the throttle response. If I run the engine for more than 10 seconds on full speed the engine will stop almost immediately when I try to throttle it back to idle. I have adjusted the full speed needle to about 1.5 turns and I have also tried almost every setting possible on the idle screw. The engine has been run about 2.5 litres of fuel but there is no sign of it getting better. The tank pressure seems to be fine and the fuel plumbing looks fine.

I have flown the plane 2 times with this engine and both flights ended up with a dead stick landing.

Has anyone had a similar experience with this engine?

I'm getting real frustrated about this so any help in this matter would be very much appreciated.

Happy flying
Sondre

RE: OS 70 Ultimate problems
 

First off, fuel with a 15% oil content is a fuel with too little oil. O.S. states that the fuel should contain at least 18% oil content by volume. With too little oil in the fuel, the engine's not getting proper lubrication, and your engine could be quitting because it's trying to seize. It won't take much full-throttle running with too little lubrication.

RE: OS 70 Ultimate problems
 

I too face problems with my engine. I broke the engine in according to the manual and I'm running 20/20 fuel. I have tried 20/15 fuel with no change.

The problem is this.

The mixture adjustment starts at 2 turns from fully in. As the engine runs, it gets richer and richer throughout the "run" to the point where I'm only about 1/2 turn from fully in when the tank finishes to keep the same rpm's. (12 oz tank)

It's just the opposite of a "normal" engine which runs leaner as the tank empties.

If I try to leave the setting alone, it gets so rich it does not want to run, bogs down and quits.

I have plenty of pressure in the tank, (too much?) Fuel delivery is NOT a problem.

The engine ran PERFECTLY the first time I flew with it. I was SO delighted. :D I attempted to fly again after a couple of days of not flying, and have not been able to get the engine to run properly since it's first flight. [:o]

The regulator isn't damaged, nor are there any obstructions in the "hole".

I have worked on several engines, so I'm not new to the hobby, and I'm a pretty good troubleshooter. But this one has me baffled! It's also my first 4 stroke, and pump setup.

ANY advice would be appreciated!

p.s. I did notice one the "o" rings on the (Idle adjustment??) was slightly damaged. I do have parts coming in this week, and will try that. If that does not work, it's possibly off to OS for repairs.

RE: OS 70 Ultimate problems
 

I Don't think the fuel with 15% oil is the problem, I have used this fuel on all my engines (both 2 and 4 strokes) for several years without any problem at all.
This weekend I tried to run the engine at several different fuels with more oil but the problem is the same, when I run the engine at full speed it leans, and when taking it back to idle it gets to much fuel and stops. It looks like the pump doesn't work at full speed and pumps to much fuel at idle.

I have been running the engine almost 2 gallons of fuel this weekend and tried almost every needle settings possible. I'm not new to 4 stroke engines and several other "experts" has tried to get this engine running properly this weekend with no success.

Any advice?

Sondre

RE: OS 70 Ultimate problems
 

Threedee,

If the engine has problems on a variety of fuels, then it's certainly possible the pump had a difficulty. Does the engine do this on a test stand, or only in the airplane? If it operates normally on the test stand, then the difficulty would come as a result of the airplane/engine/fuel system combination.

If all else fails, please send the engine to us for coverage under the warranty.