Here are 2 pictures of the engine in case it makes a difference.

         Chancey. the needle your making reference about was discontinued some years back. Your engine is from the 1980's. It predates the 40th anniversary engine which became available in and around the mid 80's.  The replacement needle that Fox sold was the full tapered needle. While it does screw in and works, I've had some issues with it in SOME spraybars. Some of the spraybars over the years have changed slightly in appearance. Some had black oxide finish, others brass, and  some were plated. Depending on the years they were made the replacement does one or two things. It either works, or it's barely hanging on by a thread or two to allow it to run correctly. It's not uncommon to have any Fox needle break off especially in a inverted landing. Essentially there's two knobs on the needle, one for the ratchet clicker and one for your fingers to turn. I always cut them off above the ratchet clicker and bend into a J to avoid bending. The needle are dead soft, if you try and bend them back, they will break. They break at the first thread on the needle just at the start of the taper. Typically they're broken off in the spraybar leaving the tapered portion inside and the rest snaps off. I'm not going to say it's impossible to straighten. However, due to the poor quality of the entire assembly, it's far better to improve your engine runs by just replacing it in it's entirety. Seeing that Fox has been out of the engine industry for a few years now, EBAY has been a fairly good source to find needles. Omni models / Tower Hobbies has had Fox needle on Buy It Now auctions  recently. I don't know where they're finding them, but they just recently went out of stock with a supply of over 75. I would keep an eye out or post on here for a new in the package one.

               In my opinion, the best needle to use is a Randy Smith needle. For the cost, there's nothing better. Randy might not have these in stock but it's certainly worth asking. I've seen new in the package Fox needles sell for just as much as a Randy needle so it's pretty much pointless to buy a Fox needle. RSM also sells a Super Tiger copy which is designed for the Fox. I have no experience with that needle. Super Tiger the originals were very large in comparison to the Fox which could rob some needed rpm's if used. I assume the offering from RSM is the correct throat diameter. If you take out your stock Fox spraybar you will note that the center is turned down, this is exactly how Randy Smith needles are done.  Ken


                

Ok. As I am new to anything bigger than .049, and having only run RC engines larger, when referencing outlet hole in your post, could you please verify my picture. To me, this is how I see it.
A - red line is perpendicular to the venture
B - green line is parallel, or 90 degrees to the venture
C - blue lines, 15 - 45 degrees with improved suction by test

Again, this is how I am interpreting your post. If I am seeing or thinking this all wrong, please let me know so I can correct it. Thank you.

An easy way to remedy the larger Tigre needle is to file flats on it both sides of the hole.  This still leaves plenty of metal on the top and bottom for strength when tightening the spray bar nuts.  Leonard Newman's idea, by the way.

Clancey,
Couple things about the old Fox that will make your life easier. First you can change the nva to the Randy Smith option, RSM or even an OS 35 - 40 FP nva. Trick is to seal around the mount boss with silicone sealer when you seat the spraybar nut. If you use a Fox nva you need to look at the spraybar holes as they are drilled below the centerline. This is to position the holes just below the 90 deg line in your drawing. They (the Fox nva) do work but you need to also seal the needle itself with a small piece of silicone fuel tubing between the spraybar seat and the ratchet clicker. Last, run the engine on 5 - 10% nitro with 25% oil (50/50 works well) and a 9x6 prop if you run a muffler.

I like the Fox for OTS and once I pulled back the prop from a 10x6 to the 9x6 with the muffler the motor runs in a nice lean 4 cycle and moves the ship nicely.

Best,   DennisT