Hi All:
I am thinking about adding a remote nva to one of my OS .35 powered profile stunt planes and was concerned about what advantage if any. would there be in doing so.
Perhaps the fact that my fingers will be in a safer position when adjusting the needle valve. I have an OS .40 with the remote needle valve on profile stunter and I have grown to enjoy the extra distance from the spinning prop for safety reasons. At the present time, I have an OS.35S with a ST nva which is more or less the standard replacement for these engines. It works very well but, my fingers are still close to the spinning prop.
I have the complete remote nva assembly to drop into the .35 to replace the ST nva. Oh yes, what would be a suitable venturi bore for the remote nva set up if I decided to make the change?
I haven't found any significant issue with remote or rear needle systems on several systems. The only problem was figuring out how and where to mount it, in the case of remote needles. Most of the analysis related to "lag" is wrong, the lag simply from having the needle 2" away is well under a millisecond. There may be other effects but I haven't found any consequential performance issues.
The original OS 35S needle is probably superior to the ST, I sure wouldn't change to the ST for performance reasons alone. People do it all the time and usually it's OK, but you're not gaining anything much and adding the chance of the ST turning into a tuning fork occasionally.
The choke area should be the same, remote needle or not. Presumably you are using a conventional spraybar with the needle hole blocked for the spraybar, so it should be the same size as it was before.
Many people, without realizing it, replaced the OS with the ST spraybar and concluded it "needled better" - which in some cases, it does, because the ST spraybar is much bigger around than the current OS needle. On the 20/25FP and 25LA, that has the super-great effect of killing about 1/3 the power, what a great modification, then you can go on the internet and tell that idiot from California that he's a liar (as has happened repeatedly). On the OS-35s, the original spraybar was also 4mm like the ST, so at least you don't change the choke area, and you can put the original spraybar back in because the case and venturi haven't been damaged, er, "modified for lucky best stunt run".
BTW, the "core" of the OS RC carburetor can be unscrewed and used as a remote needle/metering block. OS used to sell it for that purpose. So if you have any 80's+ OS RC carbs lying around, you can use that. Just like the front needle assembly, the needle is stiffer and supported much better than the ST, and you have click stops and very fine thread. If you think you need to change it between clicks, you probably have something else wrong.
Brett