Hey gang.  I have a Fox .35 that I bought about 25 years ago, built a plane around it, but could never get it to run.  It always started fine on prime, but wouldn't take off and run.  The plane got detroyed in a house move, and the engine has been sitting in a box since then.  I got it out last week, mounted it to a board, and ran into the same problem where it won't pick up fuel.  I tried the tank at different heights compared to the needle valve with no difference.  The spray bar is free of obstructions, and the crankcase is leak-free.  I want to use my old/new engine.  Can anyone offer pointers?  Thanks in advance!

Put a piece of hose on the needle valve intake side and try to blow through it.  If you can't, then things are plugged up. If it is clear then choke it and turn the prop both directions.  There is the slight possibility that it has a left hand crank and will only run "backwards".    If the needle is clear and it still won't draw fuel, check the backplate gasket.  If the backplate leaks, there is no way for it to get vacuum to draw fuel.  You should also make sure that the fuel line from your tank is actually in fuel and that the line is open.  Sometimes they get plugged up in amazing ways.  I have had every one of these problems including Jim's leaking needle valve body.  The engine will suck air before fuel if it has a choice.

Foxes will run pretty rich, so I would open the needle about 6 or more turns. I have seen this happen more than once where the needle just was not open far enough. The Fox instructions say 5 to 7 turns out on the needle, and I have seen where 8 works pretty good. Once you get it started, leave the battery on until you get the needle set. Also, check to see that you can not see either hole in the spray bar, if it is a 2 hole spray bar. If it is a  one hole make sure it is pointed down the venturi.

Fox .35 can be a real kick, but if just getting back into the game and looking for easier handling and feeding, then you might ought consider procuring an OS la .46 or Brodak .40. If everything is not perfect, they will chug away a lot more consistently than the kinda persnickety Foxy gurl.  They will drink almost anything (because their cylinders are plated with nickel or chrome) and if get a lean run, are much more forgiving and will not go over the hill right away. When you learn how to make these run, then using an engine that gets hurt real bad if not handled just right, won't present the hurdles it might when you're just starting out all over again.
Shaken not Stirred,
Grady

I may be mistaken but 25% nitro on the fox is way too much. I'm no fox expert, but from what I've read so far on these forums, 5 to 15% nitro is more like it. 5% for cold weather, 15% for hot weather.

Also, more importantly, your oil content for the fox is too low. The fox should be using 25 to 29% castor or a 80% castor 20% synthetic content to get to the 25 to 29% in the end.

My fox runs on brodak's 5% nitro, 29% castor. It also runs on brodaks 10% nitro, 29% castor.

Check Brodaks website to order online.

Also, I'm with the others on the needle valve thing: Try opening it more. If all else fails with the fresh 25-29% content oil, I would change the needle valve for an st (super tiger) version, they fit on the fox .35.

Also, on these first starts, an electric starter sure gets things started faster then by hand...

After a quart of fuel, my fox starts nicely by hand.

Good luck

-Danny 

High castor percentage - Good info. Lower Nitro - Good info. Use an electic starter on a Fox - BAD  info, most likely will push crankshaft into backplate causing damage.  More good info: Stuffer back plate (should be mandatory) Randy Smith Fox NV...likewise. 

I wouldn't. The stuffer backplate makes them run smoother but the crank shaft end can still be forced against it causing gauling. The electric starter issue is not exclusive to Fox 35 either, OS 35S' are prone to the same issue. Others experiences may differ but hey, you pays your money and takes your chances.

I was mistaken on the fuel, it is a 15% nitro fuel, not the 25% I was thinking.  When I added the castor oil to the mix, that would reduce the percentages of all the other components, so that 15% would be lower, maybe 10%.  I'm thinking the amount of castor I added should be fine, the amount added was 20% of the original fuel quantity.  Or is this engine like a diesel, needing a lot of castor to get compression where the synthetic doesn't really help.  I couldn't find the oil content on the original fuel, so don't know how much there is in the mix.

  15% is fine, and it should make it easier to start. I wouldn't be too scared of 25% as long as you work up to the break-in. I used to prime my Fox with Cox "Blue Can" when I was running Fox Superfuel, makes it kick over a lot more energetically.

   Brett

What Brett said on the nitro.  Werwage and Wooley (along with many others) frequently used 25% nitro.

  Although if you do it for long, I would suggest finding a Randy crank! Either that or carry about half a dozen stockers.

     Brett

p.s. you might be surprised what these engines will run on. I recently assisted some kids of a friend of mine with an experiment where they ran a 20FP (the one that David and I flew for 547 and 542 points, respectively, in P-40 one time) on glow fuel mixed with either gasoline, or with vegetable oil. Even 50/50 gas and glow fuel ran, although with only 9% oil it wasn't going to do it for long, and it got *very* hot. It ran fine on 70/30 glow fuel/Wesson Oil with essentially no power loss, and if we had opened up the spraybar holes, it would have at least started on 50/50. As it was, with the 50/50 fuel/oil was too thick and I ran out of needle adjustment before I got it rich enough to run.

There were some Fox 35 needle valves around that required that they be open 8-10 turns for starting. I remember this from the instructions of the first Fox I had in the early 80's. Might you have one of those? I don't know how to identify them by looks, but I know the needle was flat on one side.

     A lot of them are like that. I think the issue is where the threads end relative to where the wedge starts. I used up A BUNCH of stock needles in the late 70's/early 80's and even from the same batch, one would need 5 turns, and the next would need 8. Only about 3 out of 10 of them worked properly in any particular spraybar. A particular spraybar needed a certain type of needle. And where the flat wound up relative to the holes also made a huge difference, not in the number of turns required, but in exactly how the 4-2 worked and how evenly it ran.

     This brings back many nostalgic memories of sitting out in a hot parking lot for hours on end trying various combinations of randomly-produced Fox parts (and fuel and tanks and props and glow plugs) to see which ones ran properly. It reminds me of the murderous blinding rage and dreams of finding something better and then taking every Fox 35 I saw, placing it gently on a blacksmith's anvil, and smashing it into individual quarks and gluons with superhuman blows of a 10-lb-sledge. Ah, good times...

    Brett

     I would say considering the engine is new for the most part, I think a few things should be addressed. The engine has sat for several years if I read that correctly. I would check to see if that conrod is floating freely on the wrist pin using a small allen wrench to get behind the rod and work it back and forth with some oil. While the backplate is off a new gasket should be in order due to that one more than likely getting ruined when you remove it to check the rod and also it has been squished for a long time. I generally lay the case on a piece of glass with 400 sandpaper on it and a bit of wd-40 as a lapping oil and work the case flat for the gasket area. You would be pretty surprised as to how untrue that area is. If the backplate isn't sealing your not going to draw fuel. You claimed no crankcase leaks so I will take your word and let you decide whats best to do. Just remember its very easy to overtighten the backplate and distort the ears. I would also highly suggest not only on the test stand but also once in the plane to wire tie with copper wire your fuel tubing to your fuel barb on your spraybar. This will eventually come off especially once the tubing really gets oil soaked. I would orientate the holes on the spraybar so that when looking down your venturi that you just start to see both holes looking straight down on them. I would also suggest a inline fuel filter on the test stand as to not get major bubbles causing erratic and lean runs. Although the needle valve is poor as most claim, it works with a few tricks. I'm assuming that your needle has a flat on one side because of the time frame you described when you purchased it. . If so, this needle doesn't have to be entirely screwed out to work. I would place a square clean cut piece of tubing on your needle about 5/16 long and then screw it into your spraybar. If need be, you could cut a few pieces of tubing smaller allowing you to screw your needle in more. This is the probable reason why its apparently not drawing fuel. After that , I would start it up as I see no reasoning why it wouldn't run. We cut our Fox needles so they don't get broken in a inverted landing. You clip the round knurled knob off and bend it over into a J shape. This allows one finger adjustments while the rest of your hand is holding the plane and this advice probably just saved you $20.00 in broken needles. The newer tapered Fox needles  are barely screwed into the spraybar to get them to work correctly hence the need for a larger piece of tubing on it. The older spade style is no longer available and the new tapered is the replacement. Bob Z stated above about the Randy Smith needle and spraybay. This is a well designed and affordable option. I would say that there is no needle out there as nicely made as that one and its a direct fit having the center area the same size as the stock Fox unit. I usually use a Master Airscrew 9x6 on break in and I don't break mine in on a rich run but a steady two breaking back and forth. These methods work well for me maybe not for everyone so good luck.  I surely don't suggest Brett's sledgehammering method. Ken

  It was just a wonderful nostalgic dream. My recommended solution to almost any Fox 35 run problem can be found here:

http://www3.towerhobbies.com/cgi-bin/wti0001p?Q=1&I=LXPUE2&P=3

   Brett

You know, I actually clicked on the above link looking for a shrine of knowledge on the Fox 35 - boy was I mistaken!

Nice humor though Brett.

You know, I actually clicked on the above link looking for a shrine of knowledge on the Fox 35 - boy was I mistaken!

Nice humor though Brett.

  Actually, that link is about all you need to know about the topic! So I contend it *is* a shrine of Fox 35 knowledge.

    Brett