I have a 40 FP venturi and 25 FP RC.  The 40 venturi came with 40FP Stunt.  Would it work in the 25?  What would fuel consumption be like?  Will probably have to get a Smith NVA unless I find something at the Lebanon RC Flea Market.

Would it work in the 25?  What would fuel consumption be like?  Will probably have to get a Smith NVA unless I find something at the Lebanon RC Flea Market.

If you don't want to drill out the case you need to get an OS needle valve.  Yes it will work, sorta, but see below.

If a venturi is oversize you can always fill it with JB Weld and bore it out smaller.

Or just get a pair of nylons from somewhere (I recommend not asking women on the street, though -- you can get plunged into the most unimaginable misunderstandings that way).  Cut out squares of material and hold them on the venturi with an O-ring.  You get a nice tunable restriction, an air filter, and a guard against fuel splash-back all in one.

I have to agree with Brett on the NVA and the venturi—for a 20 or 25. The good thing that it is a straight bolt in—no drilling required. Since the correct parts are readily available, why mess with a venturi that is probably too big?

I've bought quite a few to convert FP 20s and FP 25s to CL and despite what the technical notes say, all the venturis that I've received from Tower have measured 6.55mm ID—as measured with a vernier calliper that has never been dropped.

The small venturi that used to be supplied with the FP 35 and FP 40 back in the day measured 6.75mm and the large one is 7.1mm, standard in the LA 46-S, and readily available. I've simply run a 6.75mm reamer through the FP 20/25 venturi when I wanted a 6.75mm ID. It's not the purest way but it is only 0.2mm—~0.008"—so I don't think it adversely effects mixture flow.

I've seen an LA 46 fitted with the 6.75mm factory venturi work very well in a Heartbeat Models Sukhoi and the attached article may be of interest as well.

I have a late model—ABN—FP 40 with a Zambelli hemi-head, 6.75mm venturi and Bolly Clubman 11.5 x 5 in an ARF Cardinal. A very happy combination.