OS28F Venturi Size ????

[Jack R. Dock]

I am retrofitting a OS28F RC engine to use on CL.  Does anyone have a suggestion for the venturi diameter when using a ST 36 needle valve?  Its about 5/32 inch in dia.

Thanks  -------  Jack

[Steve Helmick]

I'd start with a .272" hole, but keep in mind that you can reduce your effective venturi size by using a Bruline air filter or layers of panty hose material held on with an o-ring. The Bruline "fine/green" is said to be a -.020" reduction, while the "coarse/black" is -.010" reduction. The filter is a real fine idea anyway, IMO, so don't be shy about using it. And you can always drill it out bigger, if you need to, but that should work pretty well.

I once made a venturi for a .25F or .28F, and put the spraybar through the drawbar hole. The venturi had a spigot for fuel delivery from the spraybar. I wasn't confident that it would work, but it did. It sounds like you're going to put the spraybar above the crankcase? I've done that, too and it works reasonably well...probably best for a profile with side mounted engine.    Steve

[Terry Bolin]

Jack, Jim Lee did the leg work on that for me last year using the RC carb for starting numbers. You should contact him and get one sent to ya.
T

[john e. holliday]

I am surprised that Jack didn't contact Jim first.  He has a line of venturis for quite a few of the OS engines and each set comes in various sizes.  I have at least four different ones to try on mine.  Having fun,  DOC Holliday

[Jack R. Dock]

Thanks Guys ---
Sounds like I need to chat with Jim and get one from him.  I have never tried the panty hose thing but may do that just to see what happends.

Jack