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  • April 23, 2019, 03:12:50 AM

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Author Topic: Needle For Fox .35 Engine  (Read 342 times)

Offline Chancey Chorney

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Needle For Fox .35 Engine
« on: April 15, 2019, 03:43:29 PM »
Hi again. So i have a question regarding a needle for a Fox .35 engine. My engine is older and has a needle with a flat taper on the end. However, the needle has a slight bend to it which makes screwing it in all the way very hard. I tried straightening it but did not help much. So I see a fellow online that has an older ringed Fox .45 engine that had the piston break, and was wondering if it was of any use. At a look at the pictures of the carburetor, the needle appears to look the same, but it is still installed. Does anyone here know if the needle from the Fox .45 RC would be the same as that of a Fox .35 control line engine? Thank you.


Offline Dennis Toth

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Re: Needle For Fox .35 Engine
« Reply #1 on: April 15, 2019, 05:30:29 PM »
Chancey,
I don't know if the NVA from the RC version of the Fox 45 will work. The best setup is a Randy Smith - Fox PA NVA. This has excellent seal on the needle, fits the holes in the Fox 35 case and has the center section turned down to match the OEM Fox. Second choice for just sport flying is an ST NVA for their 35, this are available from several vendors - look in the Vendors corner below. Last option is to go to MECOA website (http://www.foxmodelmotors.com/engines/35/35.htm). They have parts for the Fox including needle valve and spraybar if you need it.

Remember if you use the Fox NVA to seal around the NVA as it goes into the venturi with silicone sealer and use a piece of silicone fuel tubing between the block and the ratchet wheel (about 3/8" should do it) to seal the threads.

Last thing about the Fox is to use a uniflow fuel tank with the uniflow vent pointed straight into the free air stream, on the circle inside side of the fuse about 3/16" off the side. If a profile make up a standoff from heavy tin or brass strip to solder a short (3/4") piece of copper tubing, attach this by the rear engine mount bolt and run a piece of fuel tubing to the uniflow line on the tank. Run it on a 10x6 prop, fuel should be 5 - 10%N with 25 - 28% oil (can be all castor or 50/50 castor/synthetic), don't run low oil it will cook the Fox in a few runs.

If you are running it on a profile the stick in the bypass mod is a good thing to consider. It has been described in several recent post, do a search for Fox burp.

Best,   DennisT

Offline BillP

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Re: Needle For Fox .35 Engine
« Reply #2 on: April 15, 2019, 06:10:24 PM »
Hi again. So i have a question regarding a needle for a Fox .35 engine. My engine is older and has a needle with a flat taper on the end. However, the needle has a slight bend to it which makes screwing it in all the way very hard. I tried straightening it but did not help much. So I see a fellow online that has an older ringed Fox .45 engine that had the piston break, and was wondering if it was of any use. At a look at the pictures of the carburetor, the needle appears to look the same, but it is still installed. Does anyone here know if the needle from the Fox .45 RC would be the same as that of a Fox .35 control line engine? Thank you.

The Fox 45 needle will not fit a Fox 35...not even close.  I heated the last bent (on threads) Fox 35 needle I had and it bent back straight very easy without breaking. I left as is and didn't try to harden it back up.

Bill P.

Offline Chancey Chorney

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Re: Needle For Fox .35 Engine
« Reply #3 on: April 15, 2019, 06:55:50 PM »
Thank you for the replies. I will not pursue the needle then. Just the outside appearance had me want to ask.

Offline John Paris

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Re: Needle For Fox .35 Engine
« Reply #4 on: April 15, 2019, 07:37:13 PM »
Chancey,
It has been my experience that the slant needles have to be almost all the way out to work.  I would also guess that the bend occurred near the point where the engine needed to be set to run.  Place a small piece of silicone tubing long enough to touch the spray bar and the shoulder of the needle (ratchet piece) on the threads to help make a good seal.  Might work fine unless there is a huge bend in it.
John
John Paris
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Offline Chancey Chorney

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Re: Needle For Fox .35 Engine
« Reply #5 on: April 15, 2019, 08:01:50 PM »
Thanks. It is not a huge bend, just slight, but is harder to turn in when almost all the way in. I have tubing already on it. I will give it a test run hopefully soon once the weather breaks here and I have some spare time. I have a few engines to test run.

Offline BillP

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Re: Needle For Fox .35 Engine
« Reply #6 on: April 16, 2019, 05:42:08 PM »
Be aware the flat needle doesn't meter in a full rotation like tapered needles. The flat side has a sweet spot in relation to the spray bar holes and that's where you want it for adjusting. Hook up a piece of fuel line to the nva and blow into it while screwing the nv out...you will have more flow on the flat and less on the round side.
Bill P.

Offline Dan McEntee

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Re: Needle For Fox .35 Engine
« Reply #7 on: April 16, 2019, 08:15:36 PM »
  Also as far as the flat slanted needles, I have filed the flat bigger and longer to let more fuel flow. It doesn't take too much to let the needle trun in 2 or three full revolutions. The more the threads overlap, the better they will seal. I have also chucked them up in a drill and filed a taper on them also, and they worked OK. You just can't go too long on the taper. Towards the end of production, Fox started making the needles tapered for the Fox.35.
   Type at you later,
    Dan McEntee
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Offline kenneth cook

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Re: Needle For Fox .35 Engine
« Reply #8 on: April 17, 2019, 03:24:27 AM »
           The tapered needle doesn't always fit properly in the older spraybars. Sometimes they're barely screwed into them in order to get them to run correctly. Mecoa is offering the full replacement or just the needle. Full assembly is $25 and the needle is $13. Makes you want to go back in time and buy them. Shtterman on Ebay also offers the Enya as a replacement and in my opinion a far greater bargain and quality.

Offline Fredvon4

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Re: Needle For Fox .35 Engine
« Reply #9 on: April 17, 2019, 12:05:41 PM »
http://www.rsmdistribution.com/index.php

also Randy Smith Precision Aero (PA)
"A good scare teaches more than good advice"

Fred von Gortler IV

Offline Chancey Chorney

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Re: Needle For Fox .35 Engine
« Reply #10 on: April 17, 2019, 05:33:51 PM »
Thanks for the links and help. While I have not run the engine yet, it may not be as big of a deal as I am thinking with the needle being out that far. It is mainly at the last turn or two it gets tight. Sounds like these like to be out a few more turns. I will know more when the weather gets better and I have more time to play with teh engine.

Offline Glen Peterson / formerly pitsen3

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Re: Needle For Fox .35 Engine
« Reply #11 on: April 19, 2019, 11:17:25 AM »
This wont help Chancey because he is limited to how far he can screw in his needle valve but here is a mod I used to do to mine that helped quite a bit. The best choice would be a new valve from Randy but in a pinch or if you want all Fox, this works quite well.
The step inside the needle valve body is right next to the outlet holes. This really goofs up the metering as the flat passes the holes. I take a drill that is a tight fit when entering the body from the needle side and drill down the step about 1/16" deeper. this allows the fuel to find its way more equally to each of the outlet holes. This also means you will be screwing the needle in further engaging more threads.
There is usually an internal bump on the fuel inlet hole that will keep you from screwing the needle all of the way in. You must remove that also. Don't forget the tubing to seal the the needle to the body.
Glen Peterson

Offline Brett Buck

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Re: Needle For Fox .35 Engine
« Reply #12 on: April 19, 2019, 11:58:25 AM »
The step inside the needle valve body is right next to the outlet holes. This really goofs up the metering as the flat passes the holes. I take a drill that is a tight fit when entering the body from the needle side and drill down the step about 1/16" deeper. this allows the fuel to find its way more equally to each of the outlet holes. This also means you will be screwing the needle in further engaging more threads.

  That's great! I knew that the position of the flat made a huge difference in how it needled (and why 5 separate needles would all work differently, depending on the conditions), but never diagnosed why it was like that. The suggested modification certainly does seem to address it, too.

   Aside from that effect, I think the "cylindrical needle with a flat" was generally superior to the "full taper" needle, because the cylindrical portion was a close fit on the ID of the seat. That supported the needle on both sides, threads and inlet side, just like the old "+" sign needle. The full taper solves the problem you are trying to solve, but leaves the needle cantilevered by the threads - which just makes them even more prone to getting pounded out by vibration, just like the McCoy. Since they went to the full-taper, they had to start making the threads longer and the entire assembly out of steel, rather than the 60's brass version.

   I always used the "cylindrical needle with a flat" version, and then selected which particular needle to use from a generous supply of them that I bought (when they were 75 cents a piece...) and which one seemed to work for a particular fuel/air temperature/prop (depending on where the flat wound up when it was otherwise letting in about the right amount of fuel). The saving grace was that the entire adjustment range in the summer was about 3 clicks (one "right" setting, and one click either side), so a particular needle would be good for a wide range of conditions, unless you changed something.

    Of course, it never occurred to me to switch to the old, small, OS spraybar, which is far superior, and in any case, they were very hard to come by in central Kentucky in the mid-late 70's.
 
     Brett

   

Offline RandySmith

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Re: Needle For Fox .35 Engine
« Reply #13 on: April 19, 2019, 12:40:54 PM »
The  OS  15 FP or LA  Needle assembly  is the size for the  FOX 35,  the  20 is  larger diameter than the  fox, For those  that want to use the  OS  NVA
I use  2 very  thin washers on each side, with a little silicone sealer,  The  OS  works way better than the  stock FOX

Randy

Offline Glen Peterson / formerly pitsen3

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Re: Needle For Fox .35 Engine
« Reply #14 on: April 19, 2019, 03:05:26 PM »
K&B had 2 needle valves with the same part number but different spray bar diameters. I used to call and ask them to sort thou and find the small ones. They were about the size of the fox and fit the hole.
Glen Peterson


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