Not sure if this question has been asked and answered, I've looked and couldn't find the answer so I will ask.

I have an OS MAX 46AX in my trainer and I am getting a OS MAX 91 Surpass II with pump for my Extra 330. I have been running Tower Hobbies Tower Power 10%, with 18% oil (it doesn't tell me castor to synthetic mixture) and my 46 runs fine with it but has a tendancy to load up a bit at idle.
Now I am shopping for fuel again. I have been contemplating going to a 15% Nitro, with a 18% oil content (80% synthetic and 20% racing Castor) and here are my questions.

Will I notice a difference in the way the engine runs from 10% nitro to 15% nitro?
Will it idle better with 15% nitro?
Are there any benefits or drawback's to switching fuels?

From what I can tell both types of fuel will run fine in both engines... am I incorrect in that assumption?

Thanks,

Yes, both fuels will run fine in both engines, either 10 or the 15%. So use which one you are comfortable with.

Your 46 is most likely loading up because it is too rich either on the high speed needle or more likely the low speed needle. Or possibly both.

Many engines turn more RPM (with the same prop) with 15% nitro versus 10%. From what I have seen, the OS four stroke will probably show a bigger increase than the OS two stroke. There are engines with compression ratios too high for 15% but they are not made by OS.


Some do, some do not. If the idle mixture is really right, for the fuel being used, the OS engines seem to idle well regardless of nitro percentage.


Benefits
- potentially more power and performance

Drawbacks
- 15% costs more than 10%.
- Fuel economy often decreases as nitro percentage increases. If tank size is marginal this may be a concern.


OS Two strokes and four strokes list 10% and 15% nitro as acceptable and they recommend 18% oil. My brother and I have two and four stroke engines from multiple manufacturers. We use the same fuel (15% nitro, 18% oil) in everything.

I run a 46AX on 5% nitro and it runs just fine with good idle, good transition and no tendency to load up. There are guys at my field who run that engine on 20% nitro. Their engines run fine also. They may get more power -I don't know-, but if so the difference is not obvious. I think it's more important to properly tune your low speed needle than to worry about what percentage of nitro you run.

I believe you have gotten the right answers therefore I will ask a question. Why are you buying fuel from Tower? I buy many things from them but not fuel,Too expensive.

For my first order I bought 4 quarts of Tower Hobbies fuel. Figured it would be in quart bottles so less chance of it going bad, I can track how fast I go through fuel and in the mean time look around for other options. So I just added it to an existing order I had. It was either that or drive across town to get a gallon of fuel....

So spend 34.00, minus the 25.00 discount I got, plus shipping for a gallon of fuel or spend (cost of fuel + tax) + about 15.00 in fuel for my vehicle to get there and back to buy fuel locally and I am not sure what the price of fuel is a gallon locally.

So there you have it... that is why I used tower hobbies fuel for my first gallon....

FYI... I did some checking around, I found Wild Cat Extra Premium 15% Nitro, 18% oil on sale for 16.00 a gallon... sure beats some other prices I've seen...

and yes I bought the last two gallons they had...