Few guys here sells parts such as Venturis. Tower Hobbies has venturis and spring needles and NVA's as well.

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Personally I think that starting with an oversized venturi is a bad idea; a smaller one has better fuel draw than a larger one, and you could always machine it out on a lathe if needed. Overly large venturi's make engines run poorly, from what I have seen. I know that when Tim says to start big, he means "ever so slightly too big", but a too small venturi will be more usable than a too large one.
To me, the panty hose means that you missed on the right size, although it is a good fall back plan if you should go too large.
And, it should keep dirt out of the engine, so not all bad...

Tim is a very smart and in-the-know gentleman, and I don't mean to be a contrarian, but it just seems like lots of people have more trouble from overly large venturi diameter than too small a diameter. And, the latter seems much more flyable than the former (from my limited observation here).
Easier to make the hole bigger than smaller later, as well, even if it isn't THAT easy, it's doable generally.

The panty hose tip is a great one if you are very close, and it also confirms which way to go for the ideal size.


R,
Target

Would appreciate some advice,have la 46 nib with Rc carb and rear assembly, what's the best Venturi set up for sport stunt flying ,I don't mind the ra or would it run better with standard Nva ,also best place to get parts

   Certainly there are many very good cottage industry suppliers. But you can also do the most obvious thing:

https://www.towerhobbies.com/cgi-bin/wti0010p?&I=OSMG9340

and

https://www.towerhobbies.com/cgi-bin/wti0005p?&I=OSMG1447&P=X

   The correct size is 7.0mm (~0.276") if you use the stock OS needle (recommended). DO NOT start with a larger venturi and work it smaller with filters unless you have some expert assistance available, because you might not be able to recognize the symptoms, particularly if you are going to put it on a smallish airplane (35-sized or so). Many people get in trouble with too large venturis to "Get More Power" and then go off on a tangent with other changes (usually stacking in large numbers of extraneous head gaskets) and never actually try to get the venturi the right size. The stock venturi is about as large as you could conceivably use.

     If you have venturi(s) made by aftermarket suppliers, it makes sense to get a range of venturis from about .260 to 275. Then use the general approach in this thread:

https://stunthanger.com/smf/engine-set-up-tips/fuel-consumption-48110/msg499234/#msg499234

Every place you see "close the throttle a tiny bit", substitute "change to a venturi .005 smaller" and every place you see "open the throttle" substitute "use a venturi .005 larger". Once you get close, then you can make small adjustments with little 1.5x1.5" squares of panty hose material held on with an o-ring to fine-tune it.

     You can use alternate spraybars like the PA or RO-Jett, but that will require you to drill out the hole it goes through and doesn't provide much advantage. Teh fact that they are "continuous" instead of discrete clicks can be taken advantage of for extremely fine adjustments but it can make the unwary too prone to making tiny, irrelevant changes. Clicks are good and it's not too coarse that you will not be able to dial in the right setting - and if it is, you have an excessively large venturi.

   The venturi  sizes would also have to be generally larger because the alternate spraybars are much larger than the stock item, and its very difficult to put it back to stock once you have done it. Note that replacement crankcases ARE NOT currently available, nor are they likely to be in the future.

     I haven't run the 46LA in any of my airplanes (it's too big for my usual test goat) but I have certainly helped with many of them, as recently as this morning. Stock, straight out of the box, it's a very good stunt engine and we could have only dreamed of the sort of reliability/repeatability/power like this  back in the supposed "Good Old Days". It doesn't need much of anything done to it to get it to work very well, use ~4" pitch props, get it flying at a decent speed, adjust the performance in the maneuvers with the venturi size, and for the most part, leave it alone.

    Brett

From Brett's post above, I got the link for the venturi, but the other link didn't take me to the needle assembly.  Here is the stock O.S. needle assembly:

https://www.towerhobbies.com/cgi-bin/wti0001p?&I=LXCR49&P=M#technotes

I'm still a crasher, so when they got back in stock last month I got the three needle value pack.  I know a lot of guys have put a lot of time into variations on venturis and needle assemblies, but I'm just a plain sport flyer so I just stick with stock.

Mark

At the end of the day I'm still learning, getting through beginner pattern now without crashes , been flying a .15 size spitfire on 52 ft lines ,I find for me this has been the best to learn on,it's quite touchy I figure if i can master this I can move on ,my son flys our larger ships as he is more advanced, but getting back to the 46 la just want a good easy reliable set up, so standard Nva sounds like it would be fine , thankyou gents for all help and advice

  Cory

  " About .295 or 0.0233 square inches, which is right at the edge of the usable limits, as big as you could ever imagine using. That's why I am nervous about "starting too large" because it will work only when you permit the engine to rev up. The stock setup does work with sufficiently low-pitch and low-efficiency/small diameter props, but it is very marginal if you treat it like an ugly-looking ST46, or a really heavy Fox. Unfortunately that's what a lot of people try to do. Which strangely leads them to stacks and stacks of head gaskets, instead of venturi diameter which is the root cause.  "

 Brett  you maybe right ??  However It was 301  not 310, that is what my program showed, and using it, it seems to "act " larger than that,  at any rate the Os 20 bar is .134, the PA is .157 , that is .023 thou  smaller across the  largest point of the diameter of the venturi,  So 23 thou across the largest part  only make a .281 a .295??   that is only 14 thou difference, at any rate  doesn;t matter because  either your or my  measure  is  TOO large, and the .281 work almost perfect with a PA  ST  or  ENYA, or the  OLD  OS 40 size  NVA  which is  .155, and it is not on  the small size, its about right, because  a  .275 works very well too.   The size range on the  46 with a  .157  bar  ( ST  PA size ) is from  .265  to .285
I have 100s of the LAs  out there  and  people rave about how they run, and they are all over the country, and many other places in the world, so even ones I have in Georgia, and California, run very much the same
While I am at it  this setup will run well  with a  3.75 to 5 pitch prop
And the  Merlin Hot Big Bore  2004  runs very well on these.

Regards
Randy

    I mentioned it only because I was very uncomfortable with the "start too big and work down" plan. What that seems to lead to is people concluding the engine "runs away" and then they go grab a handful of head gaskets and a Dremel tool. I know the stock venturi will work at sea level with a low pitch prop, but anything else and it's really iffy, based on what I have seen. Profile at the Northwest Regionals made me want to cry, one screeching , sagging run after another, from a combination of "too large venturi" and "stunt props" (i.e. too much pitch). Some Brodak 40s apparently come with a .308 venturi and people were running them at 8500 rpm - or at least that's where they started.

     One thing people seem to very consistently miss is the relationship between rpm/HP and venturi size. There's another thread here where someone is trying the 20FP wth a 9-6 instead of a 9-4, and it won't draw fuel - probably because the flow rate difference is ~33 lower.

       Brett

Yep I have seen what your saying for decades, That is  why I like to get the venturi size as close to right as possible, I know from experience  the .281 works pretty well with the PA bar diameter, and the .253 works with the OS 20 bar diameter. And as I stated these setups will work great with 3.8 to 5.0 pitch props. I think the best Prop I have ever seen run on a OS LA 46 was the Old Bolly  11 3/4 x 4.25  and the  12.2 x 4.2 , I am making moulds on these, and these also work  extremely well on the  OS  VF 40 - 46 PA 40-51 , Many other engines . Its a shame the 46 LA  has been discontinued, I have about 12 left here  but  I think OS  Should have kept this one.  However I am working with the  35 ball bearing AX  and it is looking good

Randy

  I would expect that to be a very strong engine as well. The only reason I don't have one right now is that it's clearly WAY too much power for the Skyray and I am not inclined to build a larger airplane just to test engines. Although the Imitation is legal for both Super 70's and NOS30...

   Brett

I am looking for something to be in the same power range as the TT 36 or Aero Tiger, and still be  LIGHT, This engine is very light, and would be good in a  Vector 40  SV40     Dreadnought 40, Stiletto , Chipmonk, Nobler  Ares type airplanes,  It would  also be  good in  twister  and  larger  Profiles,  This one seem  to  be a good candidate

Randy