I want to use an OS FP .40 on the Primary Force I am building, unfortunately they seem scarce except for the RC types. Does anyone have experience converting an RC to a control line? It looks like I can still get FP .40 parts from OS. Is it as simple as ordering a needle valve and venturi? I read something where a shim gasket must be installed under the head to achieve control line performance? Is this a fool proof sure fired conversion or should I expect to have problems down the road?   If it will work can you outline the exact parts and the best source to make this happen.

Thanks,

Steve

I have done hundreds  of them, you can just convert it, if you want, by using a 240 to 250 venturie and the OS  NVA from the 20,  or  use a 265 to 280 venturie and a  ST or PA NVA.
The OS assembly is very thin, so it makes the size conversion  wrong for most people, as it acts much bigger than people think it will,  This was the main reason for the runaway problem that started with the FP 35 40 series.

Randy

Steve, while not in the business like Randy, I've converted quite a few.

I'm quite happy with the OS NVA Part no. 22311000. It makes the conversion a straight bolt up.  Others prefer the infinite adjustment available with the ST NVAs. However, using an ST NVA requires the crankcase and venturi be drilled out to accept the 4mm OD NVA (the OS part is 3.5mm as are the screws that hold the carb).

For a Primary Force, I'd start with the FP 20/25 venturi OS Part No. 22312000 (6.55mm ID). The now discontinued small venturi that used to be supplied with the FP 35 and 40 is 6.75mm ID (17/64"). You might like to consider buying two FP 20/25 venturis and drilling or reaming one out. Just for reference, the venturi currently available for the FP 40/LA 46 is the large venturi from back in the day when there were two.

Thr FP 40 that I'm currently flying in a Profile Cardinal has a Bob Zambelli hemi head and a 6.75mm venturi. The model is 51 oz and I'm using a Bolly Clubman 10.5 x 5 prop.

I have an OS .40FP that I bought used 20 years ago from the late Byron Barker.  This has been one of the best .40 size "normal" engines I have had!  I have used it on numerous profiles and two built up models.  Always done a great job and got Aaron from beginner to Intermediate then Advanced!
Wish I had a couple more like this one.......

BIG Bear
RNMM/AMM