I've got three OS .35-S's that all seem to have the same run characteristic for me on any model I mount them on. They only want to run consistently if they are on a "Full Honk" two cycle. Although it would be nice I'm not expecting a perfect 2/4 out of them, but what combo will provide a consistent slightly wet two cycle run? What combos are working well for some of you?

       This is a well-known problem from the good old days. We all used the *small* (of the two supplied) os-25S venturi. Unfortunately I can't recall the dimensions. Now, I would get a series of them about .005" apart, and select from those by experiment. Actually, I am sure that someone has one that they can measure, or they just know it off the tops of their heads.

      Brett

I've got three OS .35-S's that all seem to have the same run characteristic for me on any model I mount them on. They only want to run consistently if they are on a "Full Honk" two cycle. Although it would be nice I'm not expecting a perfect 2/4 out of them, but what combo will provide a consistent slightly wet two cycle run? What combos are working well for some of you?

If you are using the  Stock  venturie  it is  about .305  diameter, Too Big   try a  275 or so size,

Randy

Big Art told me some time back that the best venturi size for the OS Max S was .280.   And I'm not gonna second guess Big Art !!
So I sell a .280 venturi for the Max S....   The stock one is about .305....
thanks
Jim

Big Art told me some time back that the best venturi size for the OS Max S was .280.   And I'm not gonna second guess Big Art !!
So I sell a .280 venturi for the Max S....   The stock one is about .305....
thanks
Jim

Spot on Jim with a 0.155" dia needle body like a ST or one of randy's excellent products. If you are running the Max valve ~0.135" od body look for one of the .265 or smaller (they came in MANY different) If you've got a 0.272" the Max valve sometimes will work on muffler pressure. I say sometimes based on how worn the Max valve is. It will leak and break your heart. Get the ST or prefferably the Randy valve. and a 0.280 and you will be in a good place to start.

If you are using the  Stock  venturie  it is  about .305  diameter, Too Big   try a  275 or so size,

Randy

The stock NVA size is approx. .157 diameter,  the ..new..  OS 35 FP uses the 25 NVA  and is much thinner , so be careful that you don.t ix the sizes up and use a  .275 venturie with the New thinner spray bar. If you use a new thin one you will need a .250

Regards
Randy

I double checked and my venturis are .280. I'm also using the standard O.S. NVA. On the plane I'm currently dealing with I'm using a Hobby Fasteners tongue muffler. Sounds like I need to go smaller on the venturi.

 I'll be looking for ya at Sig Jim!

If you are using the standard  "Today" size (.134) spraybar that OS uses ,which is a 25 size you will need to go down to a .250 or so venturie, or the one that Brett mentioned that was for the OS 25 may work too, If you put in a .157 diameter spraybar , that came with the OS Max 35S , or equivilant,you can use the .280 sized ones

Regards
Randy

There's a Thunder Tiger Cyclone 10 x 5.5 (and a 10 x 6). Pete Ferguson's brother in NJ tried one and liked it. I got one of each for Pete when I sent in a "club order", and he shipped them to NJ. I'm glad to hear that the prop worked, because I have an OS .35S ABC project waiting on me. I got the Jim Lee venturi inserts. It's gonna go into a WU Excalibur that's also waiting...    Steve

1 head gasket, Randy or ST needle valve, .280 venturi, Excaliber 25% castor, 3% synthetic, 10 or 15% nitro fuel,
RSM 10X6 prop and go fly. Mine pretty much 4 stroke throughout the flight. Great classic engine.

 For informations sake the LA's come out of the box with the rear mounted remote NVA. I'm pretty sure the proper application by the book for the "accessory" NVA that I'm using here is the same for all of the .25 through .40 FP'S and LA's.

 Thanks for the confirmation Randy.