Mike, I'm no expert, but here's what I've done with engines that had an unknown break-in history.  I run them on the test stand, starting very rich.  Once their warmed up, I slowly lean out the needle until I get a 2 cycle and keep leaning it until it sags.  Then I richen it by about 200 RPM and let it run there.  If it holds the 2 cycle at that setting without sagging, I figure it's probably broken-in well enough to fly, as long as it is flown a bit on the rich side.  Fox 35's seem to like 10/6 props.  Just my $.02.   Glen

I use the Sig all castor, and like 10% nitro when I can get it.  I also ALWAYS add an ounce or so of Aero 1 oil from Randy to ALL my fuels.

10" props, just start with one in the 5-6 pitch range and take a handful with you to the field!

A HOT plug and a good battery!

For setting the 4-2, I use Lou Crane's method, I set the plane on my foot on it's out board tip.  By swinging the plane forward and back, you can accomplish much of the effects of the maneuvers, I guess.  I set it in a 2 cycle to begin with and slowly back out until it is just cackling between a 4 and a 2.  A couple of tank shimming flights is usually all that's required.  If it's a standard *uniflow* tank, I start somewhere about an 1/8th" high with the tank centerline.

I'm not an expert, but I did stay in the same Holiday Inn Express at Huntersville that Randy Smith did!

To Bill's Post#3 -

To review: Start the model held as Bill says: fuselage centerline level at all times, wings vertical, outboard tip down (your shoe is just to prevent scuffing the model.)

Set a comfortable, easy RPM that you can hear or tach RPM any change as you do the following.

Roll the wings to about 45° to one side from vertical (cockpit up or cockpit down) and check for RPM change.

Roll the wings to the other side from vertica at the same angle as above, and check for RPM change.

If there's no sound or RPM change in each rolled position, the tank is just about centered for upright and inverted flight. Might still need a tweak, which only flying can determine, but it shouldn't be much.

If, however, the engine leaned out when you rolled it to 45° cockpit up, and richened when you rolled it to 45° cockpit down, the tank is too low. Visualize it: in flight, the fuel 'feels' both gravity and centrifugal force. The fuel surface tries to be at right angles to the effective gravity of these two forces in combination. The wings-vertical starting position is just a "neutral" between simulating the direction of effective gravity for inverted and for upright. We can simulate the angles of the effective gravity, but not its force. The angles serve well enough...

An engine will lean out when the tank is too low, and richen when it is too high. Can get confusing with the engine singing in your hands, so if you prefer, recheck any RPM changes you notice a few times to make sure. Then you can point the model pretty straight down to uncover the pickup in the fuel tank and starve it off in just a few seconds. If you can put a finger over the tank vent, it's even quicker.

Adjust the tank height to correct the condition you noticed, crank 'er up and recheck. Might take a few passes through the procedure to move the tank to where there's no detectable RPM change in the rolled positions.

When you and the model are happy, shut it off. Tighten/retighten the motor mount bolts, prop, etc., clean the filter, and you can try a flight with good assurance it won't starve or flood off on you.

Another item: Fox 35s like nitro. They perform ever better with a bit more. Larry Foster (L&J Fox guy) likes to run his on 15% nitro, 25%C+3%Synth oil. He fits them particularly to run well on that mix. A good break-in - several short heat-up runs, let cool to air temp between each - for a new Fox 35 is usually very important. More than usual nitro improves the 4/2 type of run, with the power the nitro carries within itself. Nitromethane doesn't produce a great amount of heat when it burns, but since it brings its own oxygen, we can just pour more of it in. That means the engine will probably be thirstier - need a larger tank fill for the same time - but it will turn more prop more steadily because of it. Don't go to extremes in nitro, of course. Just keep in mind that it can help to use a bit more. And keep the oil % high enough, too.

Lou,
Slightly off topic, but I note that you must not have deleted your Zip Code or location ID from your profile. That means the software is trying to load the weather site which no longer seems to exist----and slows down the site for some guys. See Sparky's request ("News") up at the top of the page.

It's possible the current spray bars only have one hole to cut down on confusion and to work more like most other needles, however the fully tapered needle works fine in the earlier spraybars 9 out of 10 times I've tried it.  Somewhere around 1992 I remember Betty Fox and John Lowry attending a lot of local contests.  Shortly after news came around that they'd noticed many Fox engines with other manufacturers needlevalves.  A fairly large number of the new fully tapered needles were provided, if I remember correctly directly from Fox.  They were to be used with the spraybars already in circulation.  I was also told that if I wanted the old needles to work like the new ones, to just simply spin em with a drill and file the end round to make them like the new needles.  No mention of changing the spraybar was made.  I've got a fairly significant stash of Fox 35's, 25's, and 19's, with the old spray bar and new style needle and have only once had a problem with the new needle in a 50's vintage spraybar.  I mention it as a possible problem since it's easy to check for when switching the needle and can save a lot of frustation at the field.

The best way to get a Fox 35 running is to replace it with an LA 25 or a Magnum 36XLS

Or actually learn out to make one run right.  Along with Fox 15s, too.

It's not really that hard to do.  But there is always California excess, and there is worse.  An LA 25 is mostly garbage, way too low on power for an OS 25, other than perhaps one of the "25-S" models.  The Magnum 36 is a sweet engine, but the Magnum 25 is, also.  Fox 15s seemed a lot easier to get running "right" than Fox 35s, I always thought -- but my bunch had less trouble with Foxes (in the loop scavenged, steel cylinder days) than we had with Tigres (any kind, in the steel cylinder days). 

There are few things with as neat of a sound as a classic old 4-2-4 stunt engine run, be it from a Fox, Max-H, Max-S, McCoy, Merco, Tigre, or Veco.  It's just that there were always so many more old Foxes around doing that thing!

Just my 2 cents:  I chased the elusive Fox 35 stunt run for awhile - finally found it when I gave up my stubborn insistance on running them on uniflow vent and switched to plain suction.  Easy switch - same tank, uniflow blocked, over flow left open - instant 4-2-4 without going lean. 

Fox is easy to run. they are a little tempermental to start but most people try to put them in too big of a plane. They are harder to start in the winter and sometimes they get too hot in the summer. The timing is great for a 2-4 break and they are not the smoothest runing engine but for the price they were a good buy. Ask Don McClave how many contests he has won with a Fox 35.

I agree, the first experience with the venerable old Fox is telling.  As a pre-teen, I was highly influenced by the looks of the things I came in contact with, and in my young eyes, a K&B Torp "looked right", while the early rough castings of the Fox engines "looked wrong", so I bought K&B or Veco engines at first, not Fox.  Like Fred S., when I was below about 19 or 20, I generally preferred to set engines fairly close to their peak rpm range, and tear holes in the hemisphere, although that admittedly had a cost in worn out sleeves more frequently.

It would be 11-12 years before I bought my first "new" Fox 35, I think.  Not that I didn't own some Foxes at a relatively early point, though.  I had a 29, in an Elliott Black Tiger, in 1956, but sold engine and plane in '58, before going away to college.  In 1961, I was starting to fly some stunt occasionally, and bought out a fellow modeler completely, when he entered the military, and he predicted he'd not survive (he did survive his service in the Marines, but not his maniac bad driving).  He'd owned three Foxes -- a new 15 and 19, and an older 35. 

Elsewhere in the last day or so, in Fred S's thread, I mentioned watching Don Still flying the earlier 29- powered Stuka, and doing so at a fairly fast clip, closer to the ground than any 5 feet.  I copied the engine run he used, which was slightly "fast" compared to the speed that George A. was flying Noblers at (I wouldn't meet George until I was almost 20, and wouldn't get to see him flying for several months after meeting him), but it seemed then that everyone I knew had watched George fly somewhere, some time. 

That first (used) 35 seemed worn out to me, and I let it go, but the 19 was so good, I bought a 25 to go with it.  Still another young man I knew wanted to sell everything a year or so after that, so I finally had a 35 I kept, and used it in a Ruffy that had a too-short life span.  Before the 1960's ended, I had a half dozen Fox 35s, only one of which came to me new!  I had tried running some of them as slowly as George seemed to prefer, but the planes I tried that with were generally too heavy to get by with it! 

I also disliked Fox's NVA, and used Austincraft instead, when those were readily available, and later on, the OS Max NVA from the .20 and .25 that are sometimes called "Max-S" these days, although they were only marked as plain "OS Max" on their bypasses.  I never had much luck using props larger than 10" for the Fox stunt 35s, and despite reading a lot of hype about wide-bladed Rev-Up 10-6 props back in the Fox engine's heyday, I found those really weak for me in overheads. 

When the older TF 10-6 props were withdrawn from production, I tried a number of props, before settling on Taipan 10-5s for my own Fox stunts. 

A couple of years ago I was asked if a Fox 35 would run on zero nitro (I'm fairly well known on another forum for never using nitro) but this was a bit tricky because I've never run any Fox engine...ever. However I've got an old Fox 35 which leaks compression like a seive so I thought I might as well find out. On to the test stand, fill the tank with 75/25 all castor, couple of primes until it sounded "wet", hook up the plug and one flick later it was singing away happily to itself. Hmmm, not bad from cold but what about hot? Stop it, flick it, off it goes again...and again....and again. One day I might even build something I can put it in and find out about the dreaded "burp".

Brian, that is the same fuel George Aldrich used in his Fox 35's.

Fox 35 Stunts and Cox.049's have been made over the last half-century and they are not all equal.  With only two used units in hand, you might not have a winner.

The good news is that (unlike the Cox) current-production Foxes are good.

Furthermore, running a Fox 35 Stunt on a profile plane vs an upside down or or upside right model is an uphill battle.

Amen to that. As long as you don't use a Fox plug.
OS #8, Taipan red or Enya 3.

Back then we used Fox longs and had no trouble. We also flew with 9/6 props and were at sea level. I still fly the 35 Stunt with 9x6.5 props most of the time on Ringmaster types.  Maybe the smaller prop (than most people use) and elevation helped keep the plugs alive. For the last 15 or so yrs I've used Thunderbolt hots and Fireball hots with a sprinkling of Fox longs or Fox rc longs with the idle bar cut off.

bp