Despite for help! I have an OS25 LA that seems to run inconsistent.I start the engine and per instructions lean out needle valve till it almost dies then back out needle valve 15 to 20 degrees and launch. Engine performs well in level flight but today 2 times in a row after flying inverted then pulling up into a wing over and leveling of engine decides to allmost quit.After a quarter of a lap barely running it picks up pace again.Is this me leaning it out too much or do I have a tank or engine problem.The engine is stock with remote needle valve,9X4 apc prop ,under pressure using  a standand 3 oz tank and has been run at least 10x with 15% nitro fuel cut with 1/2 a quart brodak caster oil.How would you adjust the needle valve,turn in till it breaks into a sloppy 2 cycle and quit or adjust needle in till it dies and back out 15 to 20 degrees per instructions?I'm really trying to like this motor and it starts every time but I do believe its just me on when to stop turning the needle.

That's a lot of castor to add. What fuel are you using? This is a huge variable.

I fly with an OS FP20, which I've been told runs quite like the LA 25.  For that one, you want to adjust to peak RPM, then back off six clicks (which is about 15 degrees).

Keep in mind that you can consider that to be a starting point -- your tank and engine set up may require you to start out a bit leaner or richer.  But I'd always go a set amount away from peak RPM.

Just came back from field and my problem is starting to be consistaint. As soon as I flip the plane up side down moter starts to loss power, fly a couple laps inverted then down control to go into a wing over and power bleeds of fast.I almost lost line tension directly over head.As soon as I level out right side up moter losses all power and almost fades off and stalls.  I also tried running rich and  running on a steady 2 stroke setting.Is this a fuel delievery problem to were I should try running a uniflow tank and no muffler pressure or should I start taking thinks apart to look for something else?

Just came back from field and my problem is starting to be consistaint. As soon as I flip the plane up side down moter starts to loss power, fly a couple laps inverted then down control to go into a wing over and power bleeds of fast.I almost lost line tension directly over head.As soon as I level out right side up moter losses all power and almost fades off and stalls.  I also tried running rich and  running on a steady 2 stroke setting.Is this a fuel delievery problem to were I should try running a uniflow tank and no muffler pressure or should I start taking thinks apart to look for something else?

    It should run in a constant 2-stroke in the air.

   It sounds like it might be fuel starvation - I presume it is sagging lean (weak in a 2-stroke) and not loading up (losing power in a 4-stroke).

     Brett

This is a profile model with a metal tank on center line with venture.Also has a piece of foam between tank and balsa with a fuel filter in place.Engine runs are fine at level flight or doing simple wingovers giving straight up control,also does fine doing basic loops giving straight up control.Problems show up once I go inverted.

Definitely, adjust your tank height. Being centered on anything doesn't count. What works does count.  Steve

Yes, that NV Assy. will work, without having to drill the case or venturi. Some like the OS NV assy., but I don't happen to. They have a failure mode where they look good after a prang, but they are not. One click from too rich to too lean, and it won't stay running. The very best you can get is the Randy Smith "PA" NV Assy. Try one, and you will agree, I promise. Randy might even have one that's a bolt-in, but I don't know for sure.

We have a club member with a Tigercat twin, with .15LA's. One quit after 3 laps, every time. Replacing the backplate on that engine with an aluminum one (.15FP part) stopped that nonsense. Theory is that it leaked when it got warmed up, possibly from a crack. The plastic backplates tend to get loose, and lots of folks remedy that by overtightening the screws.  Aluminum is better, but flat washers and sealer can work on the plastic unit, if you're lucky. While you're at it, replace the screws with socket heads. They are metric, of course, 2.5mm for the backplate and 3mm x .5 for the head.  I don't recall the pitch of the backplate screws, but I'm sure you can get them from the LHS in the R/C car department.

You can buy a CNC'd aluminum backplate from Curtis Shipp (check the members list) for about $12 plus postage. Unless you can make one while being paid, you're better off buying from Curtis. It's sure not worth getting fired for.

You can make a backplate gasket from a postcard, milk carton, posterboard, manila envelope, etc. Not a big deal for a #11 Xacto or similar. Big hole first, then bolt holes. Bolt it on tight, and trim away the outside.

I don't recall if the notch is in the top of the backplate, or on one side. If it's at the top, it's probably for clearance of the piston (the piston skirt could well come down past the bottom of the cylinder liner at BDC).

If your tank is "standard" vented, then it will need to be somewhere close to the center of the NV or shaft, depending on mounting position of the engine (sideways, or upright/inverted). If your tank is "uniflow" vented, then it will probably need to be offset  (1/8" > 3/8" or so, usually). If the engine runs well upright but lean inverted, then you need to raise the pressure head for inverted flight...which is lowering the tank when the model is upright. Being able to fine tune the height precisely is important if you're after the best performance you can get. That requires about 1/64" adjustments. Shimming generally is more predictable than loosening screws and eyeballing the adjustment.    Steve

If you do make your own backplate, make the flange 0.094–0.0945" thick. I know that the LA 46 backplate is thicker than the aluminium part for the FP 35/40 but I don't have an LA 25 to check.

The gaskets are still available for the LA 25 if you choose to use them. At about $3 from Tower, it's hardly worth the time to make your own.

As Steve said, if you don't want to drill out the crankcase and venturi for his standard 4mm dia NVA, see whether Randy has a spraybar with 3.5mm diameter. We have them in Australia.

Cool beans! Is that a Galaxy? Supposed to be a really good flying plane...get it trimmed and working well before you push it too hard.

I have CNC'd backplates (but I was a contract machinist, so it was on my time). That was almost 20 years ago.
This is a project that came out pretty neat this Spring, on the Milltronics MB-19 CNC Tooling mill that I've been programming and running for the last 4+ years. The basic body was done entirely with a 2" Walter facemill. Good to hear that you found a good use for timecards (other than getting paid!).  Steve

I will definitely buy one more I bought my daughter a Fancy Pants that's not started yet and I have enough wood to build another Galaxy.Sorry about the double picture I will try to post the back plate picture again.Hey Steve have you ever used any streaker end mills on aluminum? We use them on or cnc's and you can really fly (8000 Rpm and 160 inches of feed at .25 deep passes).