I recently decided to get back into u control flying after a 25 yr. absence..bought some plans , old dremel scroll saw, and a fox 35. Only problem so far: I cant recall how many turns from stop on the needle to start the engine..2 3/4 sticks in my head. Is this anywhere near close?..Thanks!!..Bob

That's probably OK but another half or 3/4 turn won't hurt. Fox needles are notorious for not holding a setting because they leak air through the sloppy threads. If you can find a Super Tigre or OS needle you'll be happier in the long run.
Chuck

Have you ever tried to use thread tape to restrict the leak?

4 to 5 turns out should get it running close enough to be able to set. I usually cut a piece of fuel tubing to run the needle thru before screwing into the body. About 1/4" of tubing should seal it.
Lee TGD

Strangely enough I ran a Fox 35 for the first time ever only a couple of days ago and that was only because someone wanted to know how hard it'd be to start using zero nitro fuel. Unfortunately mine doesn't seem to have the original Fox needle valve so my setting won't be of any help but you can still do the same as I did which is just open the needle to where you're fairly certain it's going to be good and rich then just start it up and tune from there.

As for starting on zero nitro, with a clapped out piston that leaks like a seive, one flick every time. OK, a slight exaggeration because twice I didn't give it quite enough prime after pinching the fuel line to shut it down so they took 2 flicks .

I flew Fox 35's a lot back in the late 70's, early 80's. Could not get the Fox NVA to work consistantly. Put in Super Tigre NVA and all is well. Never got around to opening up the venturi as mine ran to suit me as they were. Fox changed the NVA design to be more conventional, pointy needle rather than flat, after it was noticed that most Fox engines seen at contests did not have Fox NVA's. Replacement NVA's are a noticable part of engine sales.

I have tried the fuel tubing aound the needle and that doesn't seem to do anything. Put in a Fox pointed needle instead of the flat side one and it now runs constintaly. IMO not enough air leaking past the needle to make a big differance, but others may be sloppier. The needles on my Fox RC planes seem to work fine also, however the main needle will leak a small amount of fuel out, not air in, since the tank is presurized. But not that much.

mole,

The Fox flat bevel NVA is kind of a nuisance, which is why it is so often tossed and another type installed. OS and ENYA NVA are good ones for progressive tuning, and reasonable spraybar diameter. The ST NVA are a bit big in diameter IMHO. And, yes, all three types are still available...

To make the 'fuel tube over the threads' thing work, the fuel tube snippet between the inner knurled wheel and the NVA mounting nut must be 1) cut square, and 2) longer than the space available at the running setting. That way it spring-loads the needle threads against the spraybar as well as sealing off air leaks. Part of what it does is dampen vibrations...

The flatted bevel needle tends to roam back and forth to richer and leaner as you turn it in. I see this as going richer when the flat is lining up with one of the two spraybar jets, and leaner when both jets are more masked off than directly facing the flat. This makes finding the settings "fun." Still, once you are within a half-turn on the needle, the flatted bevel works as well as any other type...

My problem with the Fox needle was that I would set the needle, fly three flights, and get three significantly different engine runs. []

That's odd, Jim...

Over the years, I've had many Fox 35 powered planes which got a one-click needle adjustment for Winter, which, like clocks where they do Daylight Savings Time, was set back where it had been come Spring. (In Arizona we don't do Daylight Savings; we get plenty of sun without it...) And that was with that awful one-flat-side monster...

I’ve read this post very interesting and you are right about the Fox needle valve screw in it’s pretty sloppy. I did not change the assembly because super tiger, K and B, and OS. And other assembly’s have a much larger hole? There is a product called fuel lube. I simply place this jell on the threads of the needle valve only. It coats the threads and really seals the Fox Stunt 35. Fuel does not seem to effect the fuel lubeAJ.

Well I tried a new approach in setting my fuel control I set at 1 full turn of the needle valve, and prop the engine if I don’t see fuel in the feed tube I will open it a quarter turn and place my finger on the Venturi, and continue flipping the prop.Repeating that quarter process until I see fuel. Complete this process until get delivered into the Venturi. Then I apply voltage to the plug. Third flip every time she starts it’s usually lean so I riches it up. I have a feeling all my Fox Stunt 35 s will be a different setting. Wish they still made the clear plastic tubing. Lots easier to see the fuel flow. If you see air bubbles in the fuel. Plug you fuel tank overflow tube. That’s the tube that vacates fuel when the tank is full. If you have a fuel vent off your crankcase or muffler. There is a leak someplace! AJ.

Yesteryear: I had a Fox35 stunt, Fox36x Scheuerle Ported, McCoy35 Redhead
Today: Enya29, Enya45BB, K&B40 Front Rotor, OS61Max SF

Two and a half turns sticks in my head but my control line days were prior to 1975 so I could easily be wrong, and it may vary for different engines. If it starts too lean it will likely shut down, or you can use a fuel line plier hand clamp to shut it down and it will help keep your hand and fingers away from the prop. Or whatever way you prefer to shut it down. I have some of these clamps (in my shop) and plan to use them. Have not tried them yet. If it is too rich just screw the needle valve in until it starts to break from a 4 cycle into a 2 cycle and away you go....

Nylon Hose Clamp Tool Set Brake Fuel Water Line Clamp Plier Hands Free Tool Car Repair Tools Hose Pliers - ****



Plier Clamp

Ya I can see that they would be handy but my area is so small I use a set of hemostats. But I had to modify them by adding red permitex sealer to stop them from damaging my fuel line. I have 6 planes that I can fly, kinda grounded sliced up my right thumb on a saw six stitches. Really sore but only five days sense I did that. All my Fox Stunt 35s only one has a K&B NVA just two turns with it. The hole in the Venturi is noticeably larger compaired to the Fox. Two square tips and three pin head tips. Later version. Mecca has the original needle tip. But two of my engines have the flat. On the square tip model. Those are the leakers. Still use fuel lube on the threads to help seal it up. Never had much luck using the fuel tubing. Ordered blue fuel tubes four sizes one foot each size. Fits fueled garden edgers. Think I may try it. They claim they are Ethinol proof. Should be fine with my 25% Castro fuel methane mix, use touch of liter fluid in the winter. Add to my fuel half ounce, and prime. AJ