I will be using a new OS .40LA on my new Full body Oriental.
Having read several threads stating the .40 is not as user friendly as the .46LA (which I have  one running just fine in my profile Oriental), I have decided to follow Pat Johnstons Venturi Chart from Stunt News Jan/Feb 2000. It leads me to take out the .280 venturi and use a .256. I plan to use the stock OS spray bar and remote needle.
Any coments or suggestions pro or con to my thinking.
To date most guys have played with prop mfg's and prop sizes to make a better running OS .40LA. That I will take into concideration also.

What led me to want to make the change in venturi was the venturi in my .46LA is .280 and same in .40LA. I'm just confused how two engines of diffrent sizes can use the same size venturi. Perhaps the size diffrence between the .40 and .46 is not significant enough to concider it. I was thinking that way when Mike Pratt had to replace the venturi in his OS.25LA (stock.265) when he could not get a good run on his first Primary Force while flying at 5000 ft in Colorado. He changed it to .250 and decided not to use the .25 LA as a fishing sinker after much experimenting with fuels and props.
I followed suit with my OS.25LA in the Barnstormer and things ran signiffinitly better.
I'm not an engine guru, just seeking advice and a possible explanation about venturi size.
Great that Leesters engine ran good with FP front N/V.

Ty, Thanks, I believe thats what Mike Pratt found out with the OS.25LA as he was also flying at 5000'.  It worked for me. Altitude must be in the equation.
I'll try the .40LA stock and change to a smaller venturi if needed. I do have a ST needle valve assy and also the smaller venturi. Changing venturis is easier. I used a ST N/V with my LA.46 (.280 venturi) just to avoid using the remote N/V.
Metal backplate in place on both engines now.
Also have a good selection of Zingers and APC's to try.
Jerry

Bill, Your comments make sense.
I ran the new .40 LA with the .265 venturi from my OS .25LA that I replace and installed a .255. Prop was Zinger 10x4.
It ran great on the bench. Got in four 6oz. tankfuls. Ran in a wet 2 cycle and after the 4th tank it would drop out of a full out 2 cycle run after 20 seconds back down to a wet 2 cycle instantantly.
Sound like its ready to go but I think I'll run 4 more tankfuls before trying in the Oriental. Engines always seem to run good on the test stand, but this baby needled really good even with the remote NV assy. Putting in the air will be the real test. Plan on starting with a Zinger 11x5 and go from there. Have local HS ordering a 10.5x 4.5 APC to try.
Fun with engines. Love it as long as it dosn't get too complicated.
Jerry

Hi Jerry,

There is something about the 10 1/2-4 1/2 APC prop.  Usually I just suggest a starting point with props, but that prop is the closest thing I have seen to *MAGIC* in our area.  It has turned out to be the best prop for several of the schneurle engines in the .36-.40 size.  I just put one on a Leo 37 last time I flew and it worked great.  Also works on the Magnum .36 as a low cost substitute for a CF prop.  Have one on a Byron Barker TT 36 and it's great.  A good starting point I would say.

Bill <><