Hello, Joe.
Before tinkering with venturi size, IŽll give it a try with the new setup.
Just for the record, my ST 46 runs almost same power with .174 and .190 id (sprinkler type) but a lot sweeter with the first, and easier on fuel.
Give it a try, probably it will be OK.
Then, if it lacks power, begin raising the effective area drilling the insert.
Hope it helps.
Manuel.

Hello,

Manuel:  I'll take your advice and try the LA .40 as is with the ST NVA.  That is , I'll try it when (?) the Artcit weather we've been having lately here in WV decides to  give up.  Minus 2* this morning and the high for the day was only 9*. 

If the engine needs more venturi area, I can open it up later.

Ward: Great idea! I wouldn't have thought of doing that.  Might be better than boring out the venturi.

Thanks to both of you.

Joe

IF you bore the venturi too big, you can make it (effectively) smaller by adding a Bruline air filter (Tower has 'em). The green (fine) is supposed to be equal to .020" reduction, the black (course), .010". An air filter is a very good thing for your engine, and helps starting. Put a few drops of fuel on the filter and you got fumes going into your engine...perfect. Especially helps inverted, IMO. If you happen to know where you can get some gnarly old used panty hose or nylons, you can put several layers on with an o-ring, safety wire, etc., for the same effect, but cheaper and more compact.  Steve

PS: I've also seen OS engines run terrible with the rear needle valve. Probably more to do with the crumby plastic backplate, though. A good one has to get through QC once in awhile!