I have an OS 46AX on my H9 Ultra Stick 40. I have run at least 50 gallons of fuel through it without a bit of trouble. Also when I fly, I wring the living Hell out of it.
Max engines don't require an extensive break in period. In fact, they fly fine right out of the box. For mine, I used the abbreviated break in recommended in the manual. After that, I tweaked the high speed mixture over the next half dozen or so flights. Since then, I haven't touched it, and I never touch the low-intermediate speed mixture!
I recommend no more than 5% nitro with some castor as part of the lubricant. I mix my own fuel, since I use so much of it. You can buy methanol, castor oil, synthetic lubricant, and nitro at most go cart shops.
Frankly, I doubt that your problem is the engine. Start tuning from scratch according to the OS manual. Don't touch the mixture valve. If you can't get things right, you should concentrate on your fuel delivery system:
- Can you easily pump the fuel into and out of the tank without problems? If you can't, you have a pinched line.
- Are your fuel lines intact? Examine them for holes. In fact, throw them away and replace them.
- Is the clunk still atttached to the internal tank line? Better yet, replace the line with a new one. Is the clunk free to move around in the tank?
- Is the fuel tank at the appropriate level for the engine? You OS manual gives guidance.
- Replace your glow plug.
- Check your muffler to ensure it isn't leaking. A good idea is to make sure the long bolt that holds it together is tight. Also let some CA leak into the threads, so you won't lose it.
All Max engines including the AX have a reliable idle; however, you'll have to clear the carb from time-to-time if you let it idle for long periods. I have never had a Max dead stick on me unless the tank was empty. You should know through experimentation about how much flight time you have with a full tank and then use a kitchen timer or your computer radio.