John,
From your description it sounds a little like you have a plug problem. I have had good runs with a hot Enya#3 plug (I have also used the Fox plug work but not always, sometimes they get taters on them and don't hold the setting).

The Fox is a special engine and once you get the hang of running them they are a very good stunt motor for the right size ship, which the Ringmaster is just fine. Not knowing how much you have run stunt engines I will give a few basics (if you know this stuff please forgive me). Break the engine in slow on the Brodak 5%, 28% oil fuel, 9x6 prop, Enya# 3 plug (this is a good starting place, a Fox plug can work but may not). This takes about 10, 5 minute runs. On the last three runs do some lean-out bursts where you either lean the needle a bit at a time or pinch the fuel line to cause the engine to lean, holding this a little longer (20 sec) several times during the tank run. Once it will hold a lean run its ready.

OK, mount the engine on maple mounts, don't use hard Aluminum pads or if you do add 1/32" plywood pads under the mount lugs (to allow some crushing under to account for the mold draft angle of the mount lugs). Mount the tank so that the back end is kicked out about 1/8" and the centerline lined up with the upper head fin (the Fox likes the tank a little high and the first fin on the head is a good start point). Last, assuming you are using a uniflow tank set the vent up in the free air stream (see the attached photo).

For the first flight set the engine on the rich side so that if you pick the nose up to the 11 o'clock position it just breaks into a 2 cycle.  Once you get a feel for how it runs you can bring up the rpm a few clicks at a time to get the lap time in the 4.9 sec (assuming 60' lines).

If you start doing maneuvers you will likely develop the Fox "Burp" on outsides. This is what they do and it can be eliminated by running more of the 2+-2_2+ setting or do the stick in the bypass (see attached).

Good luck,    DennisT

Brodak was out of 10% nitro. I haven't had a Fox in 50 years . I appreciate all the input. Trying to maiden my first Ringmaster in 50 years. I need the needle you referred too. I have accumulated 6 Foxes and finally got one to run a full tank but the needle is all the way out. I am anxious to get my Ringmaster in the air.

Brodak was out of 10% nitro. I haven't had a Fox in 50 years . I appreciate all the input. Trying to maiden my first Ringmaster in 50 years. I need the needle you referred too. I have accumulated 6 Foxes and finally got one to run a full tank but the needle is all the way out. I am anxious to get my Ringmaster in the air.

   The components of s standard, stock Fox .35 can be anything but consistent, but if you have good fuel, good battery and a good plug, they will run. I have had Fox .35's that had to have the needle backed way out, which is where I tell people to start with the setting anyway. Back it all the way out, slide a length of fuel line over the threads the length of the threads, then put it back in about 2 turns. The threads leak air something fierce sometimes. Not to start it. If it still runs too fast, take the needle back out, file the flat taper on the end of the needle a little bit, then try again. You will eventually get a decent ratio and be able to get settings. If the engine has compression but is well used, it may be varnished up and will need to be cleaned up. That can drag a Fox down and run like it's blubbering. Check the piston to see if the baffle is at the back of the cylinder bore, and has not been assembled backwards. All the other modifications that are mentioned work and work well, and I have used them, but it is still possible and very satisfying to get a good run out of a box stock Fox .35 every now and then. It helps to give you an understanding of what all the other modifications are doing and why. You don't know what you can get out of an engine until you learn to get what you can out of it in it's original designed state.
   Type at you later,
    Dan McEntee