Hey guy's can you give me some advise as how i should setup this Fox 35 from glow plugs to fuel and what tank i should be using.I can't get it to continue running wheni start trying to do stunt manuvers.Help
Thanks Jim [&o]

That is a tall order but here is what worked for me and seems to be the same for now.

Fuel: 25% or better oil, at least 1/2 castor. 5-8% Nitro. Expect minimum of 3/4 gallon for running in. See below.

Prop: smaller than flying. 9-6 wide blade wood. 10-4/5 Keep it rich most of time for first 30 minutes.

Tank: standard wedge shaped tank with pick-up at rear. Lots of variables on tanks.

Glow plug: Preferably an idle bar. Generally a "hot" plug.

If you can find one (I have bought a good supply on eBay) replace entire needle valve assembly with an OS 29-40 CL size, Enya same size, or possibly even an old K&B.
Use washers to get spray-bar hole in direct center and faced STRAIGHT BACK WITH HOLE JUST OUT OF SIGHT.

I use wildcat fuel and have 5%N 16% oil 80-20 syn-castor and 10% nitro 18% oil 80-20.

I mix 1/2 gal 10%N with 32 oz, 5% N 80-20 blended oil. Mix in 14oz. of castor oil and you have roughly 110 oz. fuel with 7.8% Nitro, 27.8% oil at 56% castor and 44% syn. It works for me very well.

Hossfly has it all covered but I'll add a bit...............

If you're wanting to fly it on a full stunter (like the type it made it's reputation pulling) it was made to run at a 4cycle in level flight. You try for a needle setting that does the 4cycle level, but the centrifugal force from a maneuver will cause it to break into a 2cycle. Adjust until you get that performance, and it'll be running cool enough from the intermittent 4cycle laps that it won't quit until the tank is dry.

The Fox Stunts were not made to be fast, they were made to run sedately, so to speak. I've seen new ones that act just like yours, that shut off if 2cycled continuously. The pistons in older engines aren't new alloys. The heat builds in them if they're not broken in until the expand too much.

They need breaking in, and the rich needle setting described above to operate like they did when they made their reputation.

BTW, if you're using the OEM needle/spraybar, their orientation in the venturi is critical. His advice to replace the spraybar and needle is good. And his advice about which works is good too.

Jim, if your Fox is already broken in and you are flying a profile, some folks have suffered what has come to be known as the "Fox burp".

If this is the case, the most common "easy" cure is to pull the cylinder and wedge some wood in the bypass to decrease the bypass size. Some make a more permanent cure such as using JB Weld but with the wood, you can easily remove it if it doesn't fix your problem.

George

Hossfly,da Rock & George, Ok guy's let's talk fuel, i don't have access to wildcat fuels.I do have access to Byron fuels, that is 20% total oil content blend, 5% or 10% nitro if i used one of these and added 4oz of castor to a gallon, would this be ok fuel to use?

Engine is used but should i go through a breakin process any way? And what process should i use? Do i use a 9x6 prop to do this?

Hossfly you mention using a glow plug with adle bar, i thought the idle bar GP was for RC type engines.Also just confirming it does take the long plug correct.Does the brand of GP make a big difference?And you say i should be using a Hot plug.I do have a enya needle valve assy that is for the enya .35 so i should use that correct.

Da Rock, on needle setting when i go to fly should i set it so it is just breaking in and out of the 4-2 cycle, or should it be in just the 4 cycle mode on the ground?

George, it is a profile and it is a used eng don't know it's history but looks to be in good shape compression seems good no sloop in crank shaft area or connecting rod.I will probably do a breakin just to be sure.
You mention the Fox burp, can you tell me how i would know if this is happening.All i know now is, that any time i try to go inverted it stops.What should i look for to know if it is having that fox burp.

Thanks guy's.

jayseas,
The three of your issues.........

needle setting:
Everyone I knew who campaigned Fox35s set the needle by test flying. In your case, you already know it's too lean to do the 4cycle-2cycle break. It's gotta be doing the 4cycle on level flight. So in your case, simply keep richening until the sucker comes down to a 4 after take off. It's obviously not doing that now, is it?

new/old engine:
If it's not new, and it has gone through a breakin, it shouldn't need another. However, old engines that look like a honey-baked ham (baked on glaze all over) actually do what you describe because they've got bake-on insides. Competition flying often gave us well used engines that needed internal cleanup. There would be a glaze on the cylinder wall that was the cause.

fuel:
Any popular fuel can be what you start with, but it'll be better to start with one that's at least got some castor in the oil content. Just add whatever amount of castor needed to bring the RESULTING amount to have 25% oil content.

128oz to a gallon. 18% original oil would mean 23oz of oil to start.
Let's make a rough guess that the resulting quantity would be around 140oz. If we add 12oz to 128oz that'd result in 140 total. Add 12 to 23 and that'd be 35oz of oil in that 140oz of fuel, and we'd get........... hey, the 35oz of oil would be 25% oil in the 140oz of fuel.......

Hmmmmm..... that's different than, "....wheni start trying to do stunt manuvers." Not much, but it suggests the tank might be high. Depending how you get to inverted, it might be high or low. Any way, it might not be in line.

What kind of tank?

OK, I just noticed the 20% oil post.

We want to wind up with 25% at least. Since the base fuel isn't all castor, and Fox was serious about wanting all castor, lets try to wind up with something like 26 or a bit more.

One percent of 128oz is about 1.3oz. Needing 6% more, but knowing the resulting amount is going to be about 140oz, lets try 8% times 1.3oz. That'd be about 10.5 oz. Add about 10oz to the gallon of fuel that's got 20% oil, and that'll be close enough.

BTW, Duke Fox really wanted you to use all castor, but he was wrong about that. Plenty of Foxs today run on synthetic oil. They've always needed to be run rich, and with today's good synthetic, rich is good enough. Well, better than good enough.

It's Brodak 3 oz
standard wedge shaped tank . And i have tried raising and lowering.

Also what about glow plugs?

A bad plug can cause those problems, but only because it's bad, not the wrong temp or type. Wrong temp has got to be really wrong unless the needle is also way off. Usually............

What plugs would you recomend?

First, you need a uniflow tank. It is difficult to get an open vented tank to run well. If you are using a muffler, run muffler pressure on it. I am presently flying a Fox stunt 35 which I bought in 1977. I lapped the piston and cylinder and broke it in on short runs with a 9 x 4. A half dozen runs and I flew rich lazy 8's with it for three or four flights as George Aldrich advised. I could not get consistant runs with the Fox NVA and replaced it with a Super Tigre NVA. I flew 11 x 5 wide Zinger props, Don't recall what fuel I ran. Last couple of years I have put several hundred OTS flights on the engine with Sig Champion 10% nitro, 20% oil, half synthetic, half castor. The engine has outstanding compression and usually gives one flip starts. Fox 2 volt plug, and Taipan 11 x 5 prop. The engine is upright. If I rich it up a hair, I can get a burp in the center of the horizontal 8's. I'm running a uniflow tank with pressure off the world's smallest and least effective muffler. It is a piece of tin which covers 1/4 the exhaust and has a pressure tap.

Can you post a picture of your muffler?

Before I started mixing my own fuel, I was dosing a gallon of 10% nitro Morgan Omega with a pint of extra castor and running a hot plug. On a profile, raise the tank so its pickup tube is just over 1/4" above the engine centerline. I've found that cures the "burp" on outside maneuvers pretty well even when its running real fat and won't make a 2-cycle break.

Hi JaySeas,
If the tank remains a problem there is a pretty good solution I've found. I have gone to plastic clunk tanks for the Fox on a profile as described by the Sig Primary Force ARF manual. The set-up runs beautifully even when put together by 11 year olds. I think the manual is available online.
Chris...

Thanks Chris for that info, I went to sig online and read the manual on the tank setup.Good info.
Jim

Here is a picture of the muffler. The fuel line in the front of the picture is the closed off overflow line. The fuel line from the muffler goes to the uniflow. The muffler has a piece turned into the exhaust so that the pressure tap is sitting in a box with anopening toward the piston and liner.

Jim thanks alot for posting the picture very simple.
Thanks Jim

Most of the plugs sold for everyday flying are "Hot" plugs. Cold plugs are for higher nitro and more RPM. Plugs have deterioted in the past 10 years due to the price of platinum and the plug makers have discovered modelers will pay the price for whatever can be spread around the flying fields as "The Best."

Since I buy plugs in bunches, I have 3 that generally serve my purposes, because I don't do 70% Nitro Pylon as I once did.

The McCoy 59, relatively hot and good for up through 15% nitro in the compression ratios of most of today's standard engines.

The McCoy 50, a fairly cold plug and good for Nitro ranges 20-40% with suitable compression ratios.

My favorite is the McCoy 9, an idle bar plug about same heat range as the 59.

I guess I learned and became adjusted to Idle Bars when my first big glow engine (Fox 29) came along and the CHAMPION GP reigned supreme. Once the high compression engines, OS, ST and K&B Greenheads dominated, they blew the ceramics right out of the Champions. [X(] Got hit one day in the forehead. Champions went back to Foxes with 6:1 CR and 5% nitro
Later, flying competition with Fox 35, Fox 40, ST 40 and a Johnson Stunt Supreme, the Fox Idle Bar was the mainstay with K&B right up there. I still like 'em.

One other thing about foxes. Is this on a profile? If so, you may need to do some vibration supression work first. If there are bubles in the fuel line, yoy may have a problem. In the order of doing things I would:

1) Right fuel, 25% oil, but not more than 30.

2) Right Prop, 9-6 or 10-5 to start.

3) Right tank yours should be fine if it is assembled properly. Check for cracks in the hard lines or fuel lines. Check the takn for leaks in a sink.

4) Good plug. I like Fox long RC, Fireball hot or magnum.

5) Vibration control stiffer nose, more or less padding under the tank tighter or looser tank mounting. Put a fuel filter close to the engine, it will break up the air bubbles. A plastic tank may help.

In my experience, most of the problem is one of the above. If it is a profle, vibration can make you go crazy figuring this out.

It is a profile and i will go thru this list to check these issues.As soon as i get this plane back together doing some mods, stiffenning the nose area and some other issues.Will post back with findings, it takes awhile have some home mods going on also.
Thanks again
Jim

I just realized my Fox 35 doesn't have the holes for a muffler.I will think of something.

Easy enough. Lots of mufflers can be jerry-rigged to fit with some help of thin sheet metal such as drink cans. Easy to use.
If you don't have a strap-on laying around, those metal circular fastners can be cut to do the job. Forget what you call them but plenty in hardware store and every so often a bag of various sizes in the Dollar stores.
Betting if you look at it and with some stuff, you will come up with ideas that you will have fun making work. Brodak handles Tung mufflers and they can be fitted with strap-on.

Which one of these NVA would be a good choice for the Fox .35
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