Someone with a lot of experience yesterday told me that once you go up in nitro content, "you shouldn't really go back down". Is there any truth to this? I ran I think 1 gallon of 15%, and just bought a gallon of 10%, and I run an OS46AX.

Thanks.

There's no truth to it. You can change nitro content up or down to your heart's content so long as you retune each time. You'll get all the yada yada about how adding nitro makes the engine run hotter/cooler (depending on who you're talking to) but so does changing plugs/props, summer/winter flying, full throttle/part throttle.

When you go up in content, anticipate the need to open the needle, maybe add head shims or take some load off the engine. I usually play with compression to find the best rpm after changing nitro %

I think the saying is only valid to the point that once you had high nitro content you will not go back to lower. I can attest to that! For my Saito its 25% and 15% feels sad its not fun at all ... the difference is tremendous.

For your 46AX 15% is just nice, no point going anymore, going less does not harm the engine for sure but too low and sometimes tuning is not as fun.

I started with 10% and my 2 strokes loved it but when I started flying 4 strokes I found they liked 15% better. Well my 2 strokes are happy with the 15% after tuning so to keep from having to buy different fuels I only buy 15% now, it works well with all my engines.

I'm not sure what they meant by that but it makes no sense whatsoever. I've tried all sorts of fuel brands and blends. You may have to adjust the needle a little when switching but that's it. It doesn't change anything inside the engine.

For your .46-AX, it really likes regular old 10%. It will run well on 15% too but that just costs more in my opinion. I even run OS 4-strokes on 10% Cool Power. People say you need at least 20% to make it idle and all sorts of other stuff but mine run just fine for general sport flying. I may switch to 15% on the 4-strokes but only if I see a real performance difference.

I have ran 10% nitro in my saitos and never had a problem, mine are older saitos and I use a caster blend fuel.

Thats another thing, I always run castor blend on my engines. The other day one of the old timers told me I should not run castor in my 4 strokes because it will cause the valves to stick and that he has always runs full synthetic. Funny thing was while he was telling me this he couldn't get his engine started and it was determined he had a stuck valve

Thanks guys. I've been using castor blends all along. I ran 1 gallons of 10%, then 2 gallons of 15%, now back to 10% (I was fine with the 10%, but wasn't able to get it the last two gallons. I now have the LHS ordering 10% for me and for the Nexstar RTF's he sells - I told him it was the right fuel to offer with that plane).

I just got a gallon of Tower Power fuel though, as I had some money to burn there. It's pink, and from recent conversations this leads me to believe there's castor in that, too, although no one at Tower seems to know.

Probably will stick with the 10%, unless I notice some remarkable loss of excitement, but I doubt it.

Missileman ... even synthetic will cause the valves to stick a bit but less than castor. Saito and YS do not recommend castor. Castor also leaves a residue, its lacquers the parts. I do not use anymore castor as its messy but if you fly often the engine should not really be affected. However, the gumming up and lacquering will build up eventually. YS do not recommend castor as if may affect the pump system.