Someone gave me a quart of Brodak's 5/29 fuel a while ago and it runs horribly in 3 different Fox Stunt .35's I've tried it in. It seems plenty oily, but they behave like the nitro content is below the claimed 5%. The engines behave like its a straight alcohol/oil fuel.

I've tried Stunt .35's on 75/25 FAI fuel and they behaved just like this stuff. Kinda hard to start, super critical needle setting, significant power loss.

The stuff smell like there's a touch of nitro in there, but it can't be right...

cutaway

Maybe try mixing a little generic 10-15% nitro sport fuel in a tank or two, and see if it helps.

Sound like the can hasn't been sealed tight, methanol evaporated and some humidity (from the air)got into the rest. The % of oil get higher as the methanol evaporate.

Na, it was capped tight and unopened until recently, and the volume was to the top, so nothing significance evaporated.

I've only ever run a Fox 35 once and that was only because someone asked me if they would run on zero nitro fuel. My engine is quite worn (someone gave it to me) but it started first flick, tuned easily and seemed to run just as well as any other engine of its type. Every time I'd stop it it'd start again with one flick, hot or cold. I can only guess that, for some reason, your fuel is bad.

Weak glow plugs?  I know unlikely on three engines, but possible.  High humidity in the air could also be an issue. 

I don't know what needle you are using, but the old stock Fox was not very precise.  The new ones should be great, no detents so you can get really fine.</p>

For whatever reason since it was given to you and is only one quart, its time to repurpose the fuel. Using it for freeing up old engines or cleaning up ones that have received a dirtbath.

John

In the seventies everybody at the local club was using FOX 35s with 75/25 castor fuel.The same for every other glow engine. Nitro was simply horrendously expensive in Italy at the time.
No starting o behavior issues of any sort , almost every engine started first flick with usually a generous prime both in the carb and the exhaust. When mufflers became a norm, only carb prime ...sure when I tried 5% nitro needle settings became way more consistent ( I even used to cut a slot in the cowl to detach the engine without disturbing the needle for not to loose that "magic" setting found ). No particular power gain over straight fuel, as far 5% nitro. Maybe with more....
Also the we always used the original FOX needle ( even if whe had lot of cheap Supertigre needle valve assemblies ) because, once used to the strange one click=lean-two click=rich behavior, no problems of any sort.
When the fashion was toward ST 46, whe had a hard time to find again that FOX built in stunt friendlyness ( 4-2-4 etc .... )

I think your fuel is good to be presented to your closest competitor ( or...maybe actual FOXes are not the same as before, who knows...)

I'd add some higher nitro fuel to it or add straight nitro to it. I always used 15% in fox's, they needle better and make more power.
Chris...

Cutaway, do you have some known good fuel for comparison, or is the gift fuel all you have to run in these motors? I'd try to get some fresh Powermaster GMA 10/29 at the LHS. If they don't have that (and most don't), get some Wildcat Premium Extra 10% nitro (18% total lube) and amplify it with castor oil to 28-29% total lube. To do this, put 4 oz of castor oil in a quart container and fill it with the Wildcat Premium Extra fuel. That'll give you 28.25% total lube, which is sufficient for the Fox. Try it and see how it compares. If that fixes the problem, you know what to do round file the bad fuel. If not, then at least try a fresh hot glow plug in the motor just to eliminate this variable.

My homebrew 7/29 mix runs fine in them.