Happy new year to all on S.H Got myself a lovely brand new os 35s ie 1977 but never used, but need a venturi and nva. I have contact details for someone here in the UK who makes them but needs the exact dimensions, (obviously!) But doesn't want the engine sent in the post. (Had 1 or 2 go walkabout in the mail) So what info do I need to pass on please? Any other advice would be welcome.. Thanks in advance
Phil

Does he need the outer dimensions, or is he just looking for the throat diameter?

If it's the latter, then Google around on "control line venturi size".  Basically you're looking to make a venturi whose open area is a certain proportion of the engine displacement (and I can't remember the number!!!) after you've taken the size of the spraybar into account.

  Problem with that is that there isn't a fixed ratio of venturi choke area to displacement and that equation doesn't make sense.   I am currently running essentially the same choke area on engines from a 20 to a 61, and David's 75 venturi is actual a little smaller than the one on the 20.

    The C/L version of the 35S used to come with two venturis, you want the smaller of the two, or, the small venturi from the 25S. I don't have either in hand but I bet somebody else does. Failing that, start with a .255-.260 (with stock spraybar).

    Brett

Hello Phil, you live just up the coast from me, I live on Sheppey in Kent! I think you can still get them from OS, or whoever is the agent here (Ripmax?) I found a brand new OS 30 R/C 70's model, and managed to get a venturi and needle valve assy. through my local model shop, Westons.

Cheers   

Thanks to all for the replies; its been really helpful. I will be using the stock muffler, so if I can't get one from Ripmax I'll ask for  the .310 internal dia AND send the r/c carb for external dia. I should have thought of that!   

   Phil, I think that will be far too big. Almost no one used the stock large venturi and it as very marginal for fuel draw.

     Brett

Thanks to all for the replies; its been really helpful. I will be using the stock muffler, so if I can't get one from Ripmax I'll ask for  the .310 internal dia AND send the r/c carb for external dia. I should have thought of that!           Neville..  I had a wonderful naughty weekend in Kent with a young lady many years ago Thanks for the trip down memory lane!

Cheers Phil   

Hi Phil

The stock venturie they came with was about .310, this was OK if you used the restrictive muffler they came with. However  most people used mufflers that flowed a bit better and found they worked much better with .270 to .280 venturie sizes. They also used a .157 diameter spray bar, most either OS or ST

Randy

         Neville..  I had a wonderful naughty weekend in Kent with a young lady many years ago Thanks for the trip down memory lane!

Cheers Phil  

Phil, was she a maid of Kent, or a Kentish maid? and do I know her?

Cheers   

The popular " village bicycle",