I have a OS 70 fl. It is giving me a little trouble. It has a great idle, and the high speed needle seems about right on the ground. When it is in the air however the top rpms sound like they go and come. I am wondering if air is getting in around the high speed needle and leaning it out in the air. It is on a 40 size stick. When it runs right is great fun, but you know when it does not well its not fun. In the past I have seen some people put a small piece of fuel tubing on the needle and cures a leaking problem. If this is the fix how big of a piece should be used? Anyway a little help would be greatly appreciated.
Alan

The best solution is to replace the O-ring.

That piece of silicone tube needs to be a little longer than the distance that separates the step of the needle and the valve body after the engine has been tunned.
In that way, the silicone will compress and will avoid air leakage.

For my engines, the silicone grease has been more effective; see this thread:

http://www.rcuniverse.com/forum/m_93...tm.htm#9359588

Your problem may not be valve air leaks, though.

Do as directed by the first responder.

If the problem persists after following the first responder's suggestions, you may be having a problem with fuel foaming. That is - engine vibration shaking the fuel tank so hard that it is causing air bubbles to form in the fuel, which varies a great deal and which can affect how your engine runs. The simple way to check for fuel foaming is to give your gallon of fuel one or two squirts of original formula "Armor All" liquid that is meant to restore plastics. If this works, then you know that you will have to find a way to isolate your fuel tank from the engine's vibration. Also rebalance your prop.


Ed Cregger

Hi!
Sounds to me that you are not certain how to set the needle (By ear)!
What you have described is a lean running engine!!! Investigate why it runs lean...high speed needle set too lean...hole in the fuel lines...tank too low ...etc.

Ed, I suggest using only a couple of drops of ArmorAll if you are going to use it. I wouldn't add it myself.

You probably know how to set your highspeed nv a few hundred rpms rich already. Either way by ear, or a dependable tach is fine. A tach is more accurate if it is a quality one.

You may be right about the highspeed leaking air somewhere. I wouldn't hesitate richening the low speed just a little bit too.

OS discontinued production of this engine, after an abbreviated production period; without bothering to look back...

I guess they had good reasons to do so.

I never saw anything positive written about it in these pages...

I agree with BLW in adding only a very little of Armor All, if any at all. I understand it contains silicones that will deposit on the glow plug and prevent the element from reacting to the methanol in the fuel. A glassy appearance to the plug element is evidence of this, which renders the plug useless.

Thanks, BLW. An excellent point.


Ed Cregger