I was figuring that I'd use a .40 LA-S in my Nobler ARF when I get around to assembling it.  But I find myself with four FP-S .25 engines.  Looking through past posts in this section, there have been LA-S .25 Noblers that are said to fly well.  I also read that with the .40/46 LA-S, the plane gets nose heavy, so that's why I was wondering on the .25 FP-S.  Also, I was flying a gimme Flight Streak with a FP-S .25 engine this past weekend.  On 60' lines I was doing 3.5 second laps.  Much faster than my FS ARF with the .25 LA.  I did not find posts by anyone who had flown a Nobler ARF with the FP .25 engine.  Anyone have this experience?

I agree that an OS 25 FP is really too small for a Nobler ARF. It might pull it around OK in level flight, but struggle in maneuvers or if it is a bit windy.

I have a Nobler ARF. I had an OS 40 LA on it and needed a bunch of tail lead to CG balance. It weighed close to 49 oz and did not fly well.

I came across and picked up the new Enya SS 35 EX BB ABC engine and put it on my Nobler. Wow, what a difference. The Enya SS 35 is designed around a 25-size case and is quite light at 7 oz. A Fox 35, which the Nobler was designed around once upon a time, weighs 6 oz. With this lighter 35 engine (compared to the 40 LA) I was able to remove most of the tail lead. Model overall weight came down to 43 oz all in (w/ stock Enya muffler). The model flies totally different at 43 oz.

Back when I was flying glow, the secret sauce to a competition Nobler ARF( besides enhancements like tip weight box, adjustable leadouts, equal flaps, upgraded elevator and flap controls and a few more) was the OS LA 46 with the  OS venturi restrictor, Shipp backplate, Smith venturi needle valve/body, ports tipped(although not a must) and a tongue muffler.  The stock muffler is where most of the weight is. An APC 11-4. Not at all nose heavy even with 4.5 ounce tank.  Of course, we replumbed the tank internally and for external air pressure. That combo could fly in sensible wind and grunt aplenty for verticals and overheads .

I ran an OS .25FSR in a Noblarf for a while. The trick was to try to keep it below Mach 0.9 with the right prop. Too much fiddling with props and fuel for different days. Plenty of horsepower, just not as tractable as you might like if you are used to running an OS .46LA. The .25FSR even though an older engine probably has more grunt than the FP, which has in my opinion more grunt than the LA.

Mark,
You need to setup the OS 25FP like they do for the OS 20FP per Brett Buck instructions. Use the stock 3030 muffler, stock NVA, stock full venturi, APC 9x4 prop, 10 - 15%N fuel. Set the CG at ~16% average chord,

With Brett's setup it will pull the Nobler better than a strong Fox35. Keep the lines to 0.012" cable and ~58' C to C.

Best,     DennisT