I have a OS 46 fx that I have been running on 15% nitro, I have heard that you shouldn't change nitro % or fuel brand. Any true to this. I'm wanting to change to 10% or even 5%.

Any suggestion?

It's currently mounted on a Great Planes P-51 ARF

Thanks

No problem changing brands or %. Just check and readjust the needle when you change the fuel.

You heard wrong. Nothing wrong with changing brands or nitro content. You will find some you like better than others after a while. You will probably have to readjust the needle settings.

You'll also probably lose a little bit of power if you switch to a lower nitro fuel. I don't think it's really enough to worry about, but that's really the only difference after you get the engine re-tuned

Probably wont notice even notice it, the fx wont have a problem.

you may notice you have to keep the idle up a bit but again were only talking 2 or 3 hundred rpm

Steven

You can even run those engines without any nitro at all. They run very well without it and you don't need to worry about putting after run oil in your engines. Nitro is acidic, the more you use the more acid you put in your engines and the more you need to put after run oil in the engines. The pylon racing guys F3D manage to fly at over 350 kilometers per hour (thats over 220 miles per hour) without using any nitro in their fuel

It's an old wives tale. Make the change any time you want. Just be prepared for a little retuning.

i have the very same engine in one of my planes and i've changed brands and Nitro % lots of times without a problem.......just like the boys say, you need to retune a tiny bit so no worries.

Thank you guys !! Its been a while since I tuned an engine, (haven't flown a plane for over a year) but I guess all it takes is to do some search in the forums

Tuning an engine is easy. You just have to remember about how it sounds when it is tuned right and how it sounds when it is not. Also, if not tuned properly, it may just quit on you causing you to land dead stick.. a sure sign you didn't tune it right..

There are several methods, and I'm sure as many people with differing opinions on how to do it. No matter how you do it, just getting used to doing it is a big first step (or in your case, a re-learning experience).

So, I won't offer a how to, just to tell you that it's easy to do and once learned, you won't forget how. We generally check the engine tune at the beginning of each flying day, then once set, if set right, you can usually forget about it and enjoy the flying.

CGr.

Here's how I set high speed needles.

Tuning – High speed needle
The following method is designed for sport flying where one wants reliable engine performance (minimum deadsticks) and long engine life (part of which comes from avoiding lean runs).

I’ll start off with a reminder that all needle adjustments should be done from behind the engine and that the plane should be firmly anchored or held. Never attempt to adjust the needle while holding the plane in the air. A small engine blip or wind gust could result in fingers in the prop.

Begin by gradually leaning the engine until you find the peak RPM. Once you find this, turn it several clicks rich. Once you’ve found this slightly rich setting, with a firm two handed grip on the plane, point the nose straight up. While you are doing this, remember to keep the propeller arc out of anyone’s face. When you raise the plane’s nose, one of three things will happen to the engine RPMs.

If the engine speeds up slightly and holds that speed for 10 to 15 seconds, pat yourself on the back (after you put the plane down), you’ve got the needle set pretty well.

If the engine slows down, or does not speed up a bit, it’s too lean. Lower it immediately, turn it a few clicks richer and try again.

If the engine speeds up significantly, it could probably be a bit leaner. Put it back down, set it a bit richer and try again.

That’s it, no magic…

..........and the (slightly more complicated/aggravating) low end tuning?

should I worry about tunning the small needle ?

Thanks,