If you are forced to use a larger needle valve assembly, just increase the venturi a few thousandth to compensate. You just need to match the choke area and the engine will not care. It had no idea what kind of NVA that is being used. This is not what I THINK, it is what has been done and discussed on the forums countless times, and is what I consider basic engine 101.
It needs a lot more than a few thousands, it needs .273 or or so (.016, 16 thousands) with an ST spraybar (not recommended) and a lot more with a PA and more still with the RO-Jett. I would measure the RO-Jett spraybar and figure out what the necessary diameter venturi bore should be, except that, apparently, someone has "liberated" my box of replacement RO-Jett spraybar and venturi parts.
If you just enlarge it "a few thousandths", you will have to run a prop with more pitch (since it won't rev up enough for the correct prop, which is an APC 9-4) and thus start giving up the advantage it has over old crock engines like the Fox 35, and your Skyray/Flight Streak will start flying like a "trainer" again.
However, there is no need to keep destroying crankcases to fit erzatz parts, a correct part is available here:
https://www.ebay.com/itm/OS-FP-LA-20-46-NEEDLE-VALVE-ASSY-DIRECT-REPLACEMENT-NIP/293139719059?hash=item44407d2393:g:0-8AAOSwJRFcolWt Which then permits you to run the stock venturi (.257") like you should.
The rear-needle setup from the OS20FP-S RN will work just fine, as well as the front needle, if you have those parts. It also works fine on the 25LA, if you have broken the backplate (but not cracked the sealing face), or if you have replaced the backplate with an aluminum aftermarket part. (harmless but unnecessary).
There is no significant question about how to run it - it's been documented endlessly since public access to the internet has been available.
I would be *extremely surprised* if anyone has run these engines in more different configurations than I have, *stock straight out of the box* is the best way.
Brett
Topic: needle valve assembly for OS la 25 or FP 20 (Read 1752 times)
