OS .25LA N/V Mod.?

Engine Men,In trying to modify my new but broken-in OS25, I followed Mike Pratt's suggestions as I fly at the same altutude.
I got a .250 ventui and Super Tigre style N/V assy.from Lenord and replaced the plastic bakplate. I drilled out the case for installing the new thicker N/V and installed it.
Well, I had nothing but problems getting a close to decent engine run with engine in my Barnstormer. Why? Mikey did it, why was mine not responding well.
After dicovering the venturi was not sealed, evedent because when I inserted the N/V spray bar into the case, it went in without having to compress the venturi at all. So I sealed the venturi with silicone and got a super running engine. Lucky me.
I now realize that when I drilled the case for the new spray bar, I compressed the "O" ring when drilling the case, that left the venturi with no seal due to lack of "O" ring pressure.
First question - What procedure should I have used in drilling for the new spray bar?
Second question - I read about the modification to the OS.46LA, to make it 4-2-4 buy raising the ports by .002. The artical basicly said if you could brush you teeth, you could make this modification. I qualify. Will I get the same results on the OS25LA? Is it worth it, since I am getting good flights with the Barnstormer. It's the first time I am flying with the engine in a full time wet 2 cycle and kind if like it, but am used to the 4-2-4 brake.
Any advice, suggestions or ridicule would be appreciated and enjoyed.
Thanks, Jerry Bohn

Hi Jerry,
I wouldn't go to the trouble of modifying the 25LA. It will probably run a 4-2 (maybe), but it will lose some power in the process. It is a lot easier to set up the wet 2 cycle run to have a much more constant speed since you are using a flatter prop. I'd stick to the wet 2.
Bill <><

"I wouldn't go to the trouble of modifying the 25LA. It will probably run a 4-2 (maybe), but it will lose some power in the process. It is a lot easier to set up the wet 2 cycle run to have a much more constant speed since you are using a flatter prop. I'd stick to the wet 2."

Same goes for the 46LA, prop it right and let it eat! The 46LA is the best control engine for the money....period!

Thanks for the replies. I will leave well enough alone.
Just for future reference for myself and others, any input as to the right way to drill out the case for replacing the stock OS N/V with a Super Tigre N/V assy. Or would you all suggest that replacing the rear stock N/V is also not really necessary?
Jerry

LAST EDITED ON Nov-08-04 AT 12:11 PM (CDT)
 
I take a 1/8th round jewelers file, chuck it into my cordless drill and *file* it to the right size, coming in from both sides. Packing tisue tightly into the opening beforehand. "Cut and try". Take your time and carefully keep it centered. A good tight fit is wanted.
Bill <><

Thanks Bill, sounds like a good and better method than I could come up with.
Jerry

The Super Tiger NVAs that Len sells arn't the same as the original. They might work ok for stunt but, they arn't made right inside.

If you want to test yours, close the needle all the way down, if you can still get air through it then it's not the standard Super Tiger design.

The problem is that the place where the needle seats is not between the fuel inlet and the fuel outlet. The seat's on the wrong side so, when you close it all the way, fuel can still go through.

I considered drilling father into the threaded end of the spray bar to move the seat but, you can't do this because they are drilled too big on the fuel nipple end. You would end up with a big hole all the way through, not good.

What you can do is drill it all the way through, slightly bigger than the needle stem so, you can use the shank (between the tapered part and the threads) as a slider valve over the outlet hole.

You're not metering the fuel with the tapered part so, it doesn't work as good but, it might be ok if you don't have to lean it down too much (stunt).

I can't say they are all made wrong but, the few I had in my shop I had to send back.

I am running a stock FP20-40 needle valve through the LA25 control line venturi. Fits in with no drilling. Runs a wet 2 cycle at a constant rpm. No hastles. Still using the plastic backplate after fifty flights.The OS needles are still available here and there. Your LHS should be able to order one, if Leonard's out. Tower should also have them. Guess you're making the Super Tigre style work now. Since the case is already drilled.

I use a .231 venturi and an OS NVA. About the same area as a .250 venturi and an ST. It runs whereever I set it, from a solid 4 cycle to a solid 2 cycle on an 8/4 or 9/4 prop, using a GRW chicken hopper tank and the stock muffler. Several more in the club behave the same way. Doesn't seem to be a real fussy engine.

LAST EDITED ON Nov-08-04 AT 10:39 PM (CDT)
 
I found I get the best runs with a Zinger 9x5 or APS 9x4. All foward uniflow tank, stock muffler with baffle intact, no pressure, no extra shim in the head. Sig 10% 50-50. Things are working well now. Sometimes engines act strange at my altitude (5000ft.), but once I worked out the bugs I created, I feel it would run well at sea level with no changes.
I have an OS40 and 46 LA in the boxes, The .46 is for a Brodak profile Oriental kit, the 40 is going in my just arrived AFR Cardinal. This time I will take the suggestions from you all as far as how to set up the engines. I did run the 40 in a Pratt Force that he published in Stunt News a couple years ago, just to see how it ran box stock, it did good, replacing the Silver Fox 40, but I wanted to save the OS 40 for later. Plane was good, pilot buried it 1" below Ground O practicing outside loops. Anuder one bits the dust!
Thanks for the great help guys, Jerry