So, after a bunch of questions this weekend about it, yet again, "setup instructions" for the 20FP and "new" 25LA. Maybe it is so simple no one can believe it, but run the engine stock with all the original stock parts from the OS Factory. DO NOT REPLACE ANY OF THE PARTS with "better" parts and the various Dremel-tool-and-a-devil-may-care-attitude grinding or drilling modifications.

   Common advice for either engine (profile mount assumed):

     OS 20FP-S ABC, 20FP-SRN (rear needle), or OS25LA-s RN ABC engine NO MODIFICATIONS OF ANY TYPE OR NATURE.
     Stock OS E2030 muffler, also stock including internal conical baffle. NO MODIFICATIONS OF ANY TYPE OR NATURE.
    APC 9-4 prop. This is the normal one with the usual APC scimitar shape. Only modification is to sand the TE with 240 grit sandpaper or similar until you can flip it forward without any chance of cutting yourself.
     Any suction tank (not uniflow, at least not to start with) where the outer edge of the tank is more than 1 3/4" from the mounting plane. Suggest Sullivan SS-4 clunk tank with "bottom" (wider) up against the fuse side
     Powermaster "Air" (basic rc sport fuel), straight out of can. 10-15% at sea level, 15-20% at altitude (for example, Tucson). The one time I ran the 25LA at Tucson, I ran YS-20/20 because it was the only 20% fuel I had. That just about made up the altitude difference between sea level and 2300 feet at 70 degrees. Other fuel (like SIG) might work as well, just do not use lots of castor oil. GMA is probably OK, Fox Superfuel IS NOT OK.

   Attach a pressure line from the STOCK muffler tap to the suction tank vent. Plug the overflow with an airtight plug. You want it to run on a suction system with pressure, not uniflow with or without pressure.

   Start engine, lean out to a 2-stroke, then slowly lean it out until it is absolutely as fast as it will go, and one click more makes it sag. Then, back off needle until you just get a distinct RPM drop, just a bit off peaked out in a 2-stroke. If you get it rich enough to start misfiring in a 4-stroke, even occasionally, you have gone *much too far*. This is about 5 clicks open from peaked-out lean using the stock OS front needle, about 5 clicks open using the 20FP rear-needle (all-metal on a metal bracket). It is about 3 clicks open from peaked out lean using the stock 25LA rear needle (gray metal needle in a plastic backplate mount). You do not need a tachometer, but it will be 2-300 RPM from peak.

   Launch the airplane and it should get slightly richer-sounding in level flight, and then peak out in the maneuvers. If it peaks out and then sags in the maneuvers, you are too lean, open needle *1* click for the next flight, try again, until it does not sag lean in the maneuvers at any point. If it ever hits a 4-stroke, you are too rich, close the needle one click and try again.

   Unfortunately, due to painful experience, YOU WILL FAIL if you make any of these modifications, so DO NOT MODIFY OR "IMPROVE" any of these items:

    Venturi: The stock CL venturi is the correct size, DO NOT CHANGE IT
    Spraybar Assembly:  The stock OS spraybar assembly is the correct part, DO NOT UNDER ANY CIRCUMSTANCES CHANGE IT FOR A "BETTER" type, specifically, DO NOT USE ANY OF THESE:

     Supertigre
     Supertigre clone
     PA
     RO-JETT
     McCoy
     Fox
     Merco
     Stalker
     Como
     Kirn-Kraft


     You name an engine manufacturer's needle, I will tell you not to use it. The ONLY ACCEPTABLE SUBSTITUTE is the Enya copy of the stock OS assembly commissioned and sold on eBay by Shtterman. Replacing the spraybar is by far the #1 most popular way to f*ck up your engine, because in addition to losing 30% of the power right off the bat, you also have to drill out the case to fit it, which means you have semi-permanently destroyed another nearly irreplacable part, and presumably the venturi, too. If you replace the spraybar, do not come to me complaining that it does not work - because I can tell you right now that it WILL NOT WORK, at least not the way I am trying to get you to run it.

    Muffler - DO NOT REPLACE THE MUFFLER WITH A "lighter/better" one, DO NOT RUN A CHIP or "TONGUE" muffler. This is extremely critical, IT WILL NOT RUN PROPERLY WITH ERZATZ mufflers. If you airplane is nose-heavy, put lead on the tail, do not remove the muffler to balance it.

     Head Gaskets/screws  - DO NOT CHANGE OR ADD HEAD GASKETS. In fact, don't even buy any "spares" because if you don't have any, you will not be tempted to use them. While you are at it, the 20FP comes with a very nice Allen Wrench. That doesn't mean you are compelled to use it!!!  Don't take the head off at all, do not replace the screws, just leave it alone. It is not going to come loose.   

     The 25LA uses JIS Crosshead screws, they are also OK, do not remove them or replace them with "better" socket-head screws. Along with that, if you have a screwdriver from any common US manufacturer/brand name (Craftsman/Proto/Williams, etc) and use it to remove or "adjust" the head or backplate screws, you will very likely damage the screws because those are Phillips, not JIS. If you absolutely must have a screwdriver, a Vessel or Hozan #1 JIS crosshead screwdriver is the only thing you should use in the exceptionally unlikely situation that you need to take it apart. DO NOT try to really crank down on the 25LA backplate, it need only be snugged up, not gorilla-tight, and if you tighten it  too much you will either cause a leak or crack it. It is otherwise perfectly OK, until you break off the corner in an inverted crash. LEAVE IT ALONE.

   You would think this would be self-evident, but apparently it isn't - DO NOT GRIND ANYTHING, CUT ANYTHING, or DRILL ANYTHING!!  Neither you, nor your flying buddies, or anyone else knows how to improve it by grinding it. Even if they did, I can assure you that if you *follow the directions*, it will be better, stock, than any other engine you and your buddies have had for the the typical 35-sized profile models like the Skyray, Flight Streak, etc.

  "old" VS "new" 25LA. I know of no way to tell whether a particular engine is the "old" version or the "new" version. It may or may not follow the paint- all of the "old"/lower-performance types I have tested or have been tested by qualified observers were the original blue-paint type, and the "new" higher-performance types have all been bare, but I can't say for sure that this is a bulletproof test. Unfortunately, the only reliable test is to run it. On the stand, the "old" types will be peaked out around 12,800-13,200 RPM with a 9-4 APC, 10% fuel, at sea level. The "new" types will spin up to around 14100-14400 on the same prop and fuel. It is not a subtle difference, and please don't tell me that "they are the same", because they are not (although I do not know what the internal difference might be, and neither will you, because, again, *you are not going to take it apart*, right?). The older types are usable but not nearly as good as the "new" type, at least for stunt.

  25FP - the 25FP will work, too, and is much more powerful than the 20 or the 25LA. This is almost a negative, because on the typical airplanes, they tend to be too fast, leading you to try to needle it down, which then makes it run less good than the others.

  Note also that the same sort of advice applies to the 46LA - dear GOD ALMIGHTY, just leave it alone!  You buddies don't know how to improve it, either. It is extremely good right out of the box, the problem being that it, too, tends to be far too powerful for the sorts of airplanes people want to use it in. Figure it to be an upgrade to an ST46 - more reliable and much more powerful. I think Tim Wescott flies one of Paul Walkers old Bad News/Impacts which originally were designed around either the ST60, 45 FSR, or 40VF.

     Brett
   

And what Brett says about the 20FP -- that.  Of the engines I've flown with in competition, the ones that stand out are the 20FP, 25LA, Tower 40 (basically a 40FP clone), a Magnum 35 (which has hotter timing than a Tower 40, and flies the same-sized airplanes), and the 46LA.  These have all been flown in as close to stock condition as I can achieve, with the exception of smaller venturies on the 46LA when I'm trying to span the gap between what a 20FP really wants to fly and what a 46LA really wants to fly. 

I've tried various older motors, and a super-duper modified 40LA, and they're not as good for serious competition.

My shop tends to be a hospice for neglected and abused equipment, so I can't follow Brett's advise about leaving things alone -- instead, I get them and put them back as close to stock as I can, and this has served me well.

   One thing that may affect things for some people is the variation in OS. needle valve assemblies. The common one most used is for the FP-20,.35,.40 and LA.25,.40 and .46. In the last couple of years I have been wanting to really study this to figure it out and prove a theory.  One version of this is the OS NVA that came with the FP-20, .35 and .40. The replacements for these came in a package with a black and white header card with part numbers and engines it will work on. I can't remember what the OD of the spray bar is right now but they worked very well, were as consistent as a part could possibly be. Then at some point in time, the packaging changed to the blue and white header card. I don't know if this was during the introduction of the LA series of engines or not. A summer or two ago I was helping a buddy with a LA.46 that required swapping out venturis and NVAs at the flying field. I knew at that time that there was a difference between the two in OD and I know that the Enya needle valve assembly looks like the OS but is different. I had purchased several OS units from shuttrman on eBay and hade a bunch of used ones in my parts box. I also heard the shuttrman was having new MVAs mad by Enya to OS specifications, so I bought a couple of those also. I can't remember the exact problem but trying to get what we want out of this engine, I noticed that the OS needles from the last batch of NVAs that I bought ( and might have been the last batch that OS produced) had really shallow tapers that were really blunt on the end. I started to treat that with checking them up in a hand drill and filing/polishing the taper to match what the older needles looked like. This greatly helped getting the needle setting that we wanted. I think this may explain the issue some guys have with "on click goes too rich or lean"  on some engines. I got the Enya made "OS " NVAs from shttrman and compared them. They looked better, but the nut was kind of a sloppy fit on the spray bar. I tried an OS nut on it and it fit better. As they come, you may easily over torque the nut and strip it out. I called Bob Brooks about it and he was aware of the issue and was working on it. I think the cause was maybe using Enya nuts on the OS spec spray bar. The difference is a matter of a few thousandths but on threads that fine it's as good as a mile. Some guys using these may not be getting them tightened correctly and they are not staying positioned correctly.
   Getting back to the last production OS NVAs, I started to compare them to other parts in my stash. It's been a while since I did this but I think I found that the last production OS FP-20 through LA.46 NVAs had s pray bar that looked just like the OS FP-.15. It made me wonder if when OS discontinued the LA series of engines, they decided to use up excess .15 NVA inventory to make up for shortages of the .20 through .46 NVAs.  The poor taper and blunt ends of the needles could just be poor quality control. I was going to mic everything up and measure things carefully and document everything and post it here, but something in life got in the way and I got side tracked. In other words, I think there may be a variation in parts out there that may be giving guys problems with these "stock" set ups. In some cases you can't buy the stock parts any longer, so you go digging through your junk box or your buddy's stuff to come up with something. Of all the things I have read over the years about NVAs and troubles guys have and all the discussions that go with that, I don't think I have ever heard once mentioned that Enya and OS needle valves do not interchange. One is slight smaller that the other by a few thousands and that is the cause of the nut issue I mentioned with the shuttrman OS reproduction when they first came out. I found out about it years ago when I went to adjust the needle on an LA.25 on a Ringmaster and I pulled the needle right off the spray bar!! Funny thing was I never felt the sloppy fit and the needle managed to stay put for quite a while, probably from accumulated dirt on the spray bar threads. Many of us have been doing this a long time, have a lot of spare parts and these get loaned, given out, sold swapped, traded and inherited. Unless you have a new in box version of a specific engine and you know all the parts are original and new, you might have to be more careful and triple check what you are using on the engine. The recent thread on FP-.35/40 runaway also brought this to mind when Randy Smith posted that you should get rid of the "tiny" OS spray bar unless you are going to use a .250" to .255" venturi, (and that is the range I usually use on OS .35/.40.46 engines with a later production NVA set) and go with something that is in the .157" diameter range, which would be PA or Super Tiger NVAs, and also the earlier FP..35/.40 assemblies with the black header card are close to that, but are getting REALLY hard to find these days. .  I think all of this is key to making the "stock" set ups work if you don't have known correct parts of the correct size.
  Type at you later,
   Dan McEntee

What do you do for break in on the LA 25? I have a Flite Streak ARF I want to throw together as a trainer just in case there’s someone who may want to learn how to fly

Is break-in and run very different for the OS Max 25's, pre FP? And the recommendations for venturi and nva, if it is being converted from RC?

Is break-in and run very different for the OS Max 25's, pre FP? And the recommendations for venturi and nva, if it is being converted from RC?

      These are good running engines, more like a traditional run, but not in the class of the FP or the LA. They are a relative of the older MAX-S .35. They made a .20 also that is not to be confused with the FP-.20.

   Type at you later,
   Dan McEntee

Is break-in and run very different for the OS Max 25's, pre FP? And the recommendations for venturi and nva, if it is being converted from RC?

    Completely different animal. I had both the OS-20 and 25-S baffle piston engines. They are fine runners, but nothing like as powerful, and certainly are not adequate substitutes for a 20FP. They are minor upgrades for the "15-sized" "Junior" models like the Flite Streak Jr, Junior Nobler, Shark 15, etc. You could fly a Skyray 35 with one, but I would expect much less performance than a Fox 35 - it's basically the same thing, with better workmanship, but 60% the size. Full patterns would be extremely difficult in anything but ideal conditions.

   The correct venturi size for stunt is 5.5 mm or about .217". With a spraybar diameter of ~0.123", this gives a choke area of about 0.0118 square inches. It came with a "small" and "large" venturi, but my experience was that the "large" was pretty hopeless on suction. Note that the spraybar was also much smaller than the 20FP, in this case, you might have to dig a lot to find a stock unit. Randy might have some. If you absolutely cannot find one, then, use the bigger OS spraybar, which will require you to damage your case fit it, and whatever size venturi it takes to get the .0115-.0118 square inches of choke area.

   It uses typical props from the Jurassic age - 8-6, 9-5, 9-6. Forget the 9-4 or smaller, and beware of breaking the crank at high revs or high nitro.

   Break-in is standard for iron-liner engines, small props at high 4-stroke settings, short runs, lots of castor. I think I ran mine for about an hour total, but I was also 12 years old at the time.

     Brett

Thanks guys.  I'm glad I asked the question because my brother and I have several.  I think we were running them like FP's and LA's. We didn't run them often.  I have one on an old Trixie which is rather light.  It pull it fairly well.  Maybe I do need some more high castor fuel and different props.  Thanks again.

   I have a fairly large B-25 profile scale model that was built by a friend who has passed away, and it's powered by two of these. I would have to get it down to look, but I think we ran 9-5 wood props on it and used spoked up SIG Champion 10% fuel, and they fly this model confidently. Sean took it to fly demo flights at Oshkosh last year. It's no light weight model either, but not a stunt model. On two engines it's pretty solid on the lines. One engine will barely keep it in the air. Dick Sarpolous published a twin engine stunt model based on a SIG Chipmunk wing that was powered by two of the .20s' I think, and certainly two of the .25s wouldn't over do it. The ARF Flight StreaK should be light enough for the .25 if you can find one of those. Might as well have a little fun with them. There are lots of the .25s around, and turn up on eBay a lot.
  Type at you later,
   Dan McEntee

The ARF Flight StreaK should be light enough for the .25 if you can find one of those.

      It will certainly fly the airplane, but will not give you anything like the performance of the Veco 19bb, OS20FP, OS15FP, etc.   Start with a 9-6.

     Brett

Brett please do a  post on running the LA 46 now.

He did -- his guidance is exactly the same as for the 20FP and 25LA.  Stock needle, stock venturi, stock muffler, don't touch anything, take it out of the box, go fly.

The only thing that I'd add to (or mildly disagree with) is that the 46LA can handle a BIG plane.  If you want to put it on a Nobler, you'll need to tone it down.  My recommendation on that is to use a smaller venturi (or the stock stunt venturi with lots of nylon mesh piled over it), and possibly go with bigger props, up to the APC 12.25 x 3.75.  If you neck the venturi down, then smaller planes seem to like that prop.

You do have to fiddle a bit with finding the prop and venturi size combination that the plane is happiest with.  The props I select from when matching a 46LA or Tower 40 to an airframe are the APC 11x4, APC 11.5x4, Thunder Tiger 11x4.5 (which I don't think you can get any more, but some may be sitting in people's stashes out there) and the APC 12.25 x 3.75.  I can't speak from experience, but I think that the 40FP would respond about the same as a Tower 40.

And -- that's it.  A bit more variability than the 20FP, but only because you're maybe trying to match it to a wider range of airframes.

He did -- his guidance is exactly the same as for the 20FP and 25LA.  Stock needle, stock venturi, stock muffler, don't touch anything, take it out of the box, go fly.

  In point of fact, I didn't, although I know that it does not need to be "carved" or "head gasket patrolled" to death, to first approximation. I do not have enough experience running the 46 LA to give this level of detailed instructions. I have "set up" dozens of 20FP/25LAs for myself and other people, and flown many hundreds of flights, in addition to doing the "small engine experiment" nearly 30 years ago, so I know exactly how it runs and how much better it is than the alternatives.

     I repeat that *I am not an engine guy* and as far as I can tell, knowing that I am not puts me way ahead of 99% of so-called engine experts. I *do* know what is required to fly stunt patterns successfully and have some general ideas about how to go about it. I have also been sad witness to the explosion of "engine experts" and their disastrous efforts trying to turn 2022 into 1955 and the very sad fact that no one even seems interested in even trying to take advantage of modern techniques. Just look at the rest of the threads in the engine forum - not a single thread and only vague references to currently competitive systems. And this is with IC in it's "end state" - this is the end (or rather, the mid-late 00's were the end), it isn't going to get any better, and IC will be either unsupportable or hopelessly uncompetitive very shortly, if it hasn't happened already.

   So, I have no detailed recommendations about how to best set up 46LAs. My best advice is if you want to run a 12-6 at 8500 RPM, go get an ST46 instead of grinding up and destroying your 46LA, so at least the next guy has a chance. The fact that this will likely spin a few people into a foaming at the mouth rant is a perfect illustration of what I was talking about.

   Brett

   

I think the only reason there seems to be utility in the extra level of fussing that I detail for the 46LA is because people need to stick it onto a wider range of airplanes.

     Sort of. The apparent desire to grind it up, add head gaskets, etc. seems to stem from wanting it to run like a "real stunt motor!", i.e. slogging along at low revs with 6" of pitch in a 4-2 break. Never mind that that hasn't been a "real stunt motor" run for well over 30 years, if you try, it will either not run reliably, or, it will decide to run like a "real stunt motor" from 1995, that is, the dreaded "runaway", which is stunt talk for "run as designed". If the airplane is too small, it will fly like a bat out of hell, and thus "obviously require modifications", if the airplane is too big, it will just be dead in the maneuvers, because you are already running it at full tilt in level flight, and the high pitch will only permit it to slow down in the maneuver. Junky foreign motors, can't even run like a Fox.

   This is when the real BS starts, because you really only have to run an appropriate prop, and then adjust the venturi diameter to get the necessary power level. However, the nearly universal first step is to start carving the head or the ports, or stacking in head gaskets - mostly because absolutely none of these guys understand the use of compression to adjust a stunt engine.  Greatly reducing the compression will indeed reduce the power - but running lower power, you cannot draw fuel - which is why it ran away in the first place!

    This starts a spiral where you get might get perfectly neat modifications, done with good workmanship or not, where you end up with 46LAs that have less power than a bone-stock Fox 35. If you don't believe me, one pretty famous reworkers engines did exactly that, to the point that the engine would not fly a Pathfinder ARF fast enough to do the pattern - even with a 10-7 prop and 15% nitro!

   The inevitable conclusion,  conveyed to me many times, is that "the 46LA is no good for stunt, and by the time you modify it to work 'right', it's gutless and you can do better with an ST46"!

   Which brings us back to Kevin's question. While I am virtually certain that there is no practical way to greatly improve a "new" 25LA (and about a million variants on how to screw it up), I actually don't know if there are simple modifications/adjustments to be made to a 46LA to make it run better. I do know that, bone stock, it seems to be vastly better overall than anything we had before about 1988, certainly better than an ST46, as long as you don't expect it to run 12-6s in chug mode. As long as you leave it alone, and pick props based on 2022 knowledge rather than 1960 knowledge, you will have a better-running engine than almost anything we used before the tuned-pipe era.

    And you sure don't want to be carving on these now-unobtainable parts trying to replicate the ST46, because you can just go get an ST46 and run that. Good luck - Ted Fancher gave up on it in 1988, but, I am sure your average Advanced pilot or expert keyboard operator knows muuuch better....

    Brett

Does the same thing about running stock and wet 2 apply to the LA 40?

   My guess - which is only that, a guess - is that yes, it will probably be a good starting point, and that you might have to experiment with venturis and prop pitch (never 6", think 5 or lower). But not internal modifications.  I don't post anything about it, because, again, *I am not an engine expert* and I have only seen a few 40LAs ever in stunt. They run perfectly well for RC peaked out lean, all you need for stunt is a lower pitched prop and a few needle clicks - not a f*cking grinder.

    It's really not too complicated, take it out of the box, do not modify it in any way, use all the parts in the box, find an appropriate prop - for a 40LA, I would probably start with an APC 11.5-4. Put it in the airplane, start it, peak it out, back off a few clicks until you get a distinct drop, launch it. Check the level flight speed, and what the engine does in the maneuvers, adjust accordingly. Play venturi off against the needle setting and the prop diameter to get the right level flight speed at the right setting (a medium 2-stroke) and the right maneuver pickup.

   I did dozens of tests like this in the small engine experiment, it takes about 3 flights per engine to know what it might need, or whether it is a waste of time. The conclusion - ANY, repeat, ANY small schneurle engine (15-32) that you could buy in the early-mid 90's *worked pretty darn well* and the parts they came with were generally appropriate for the engine. This includes the RC carb most of them come with. All gave perfectly reliable flights with very minor experimentation and generally FAR better performance than old crock baffle-piston engines. The ones that didn't do to well on the Skyray 35, Banshee, and Coyote test airplanes were the 32s, because they were FAR FAR TOO POWERFUL.

   I very strongly suspect that the 40LA is no different in that regard, although FAR FAR TOO POWERFUL to put on something like a Twister, which is where most people start making their mistakes.

   There may well be very subtle changes that will make it run slightly better for our purposes. No one will ever find them if there first step is to make a HUGE irreversible change, and, here's a clue - you actually have to know what you need to fly stunt successfully to begin to evaluate changes.

    I would note that, despite the 10,000 threads where it is discussed, *running in a 4-stroke at 8000 RPM with 6" of pitch has not been a mainstream approach in stunt for more than 30 years now*. That is way over 1/4 a century and has been around far longer than Fox 35s in chug mode. Even if you can make that happen, why do we want that?  It doesn't work nearly as well as running at 10,000 RPM and 4" of pitch, to the point it has transformed the event. You want that sort of engine, they made them for decades, and they are widely available. Why destroy new ones?

     Brett

I will try the new one - completely stock with the stock set-up from shtterman.

I have one but I modified the NVA.  However, it runs best for me with 10.5x4.5.  Runs 11 minutes on 4 oz of furel but not the highest power.

     How did you modify the spraybar - modified to put in an ST spraybar? If so, that's why you lost power, that is about 20% right off the top. It's more like 30% on the 20FP, which is why everyone insists I am lying to them.

    Brett

Yes, I put one ST size Needles in it but I I don't remember drilling it. It has a tongue muffler also.  It was my first LA engine after 2 FP 40's. I have an almost new one which I will have to convert from RC.  I want to set it up completely stock and run it that way for awhile.

If an ST-sized needle fit then someone drilled it out.

If you can't get a stock venturi for it, someone can make one for you.  RSM probably has one; Jim Lee can probably make you one.

I actually have a stock venturi which I removed from an FP 40 so I could put a (better one??? in it).  I don't remember what I put in that one.  I bought a different venturi from Jim Lee.  Then I sold the engine.  This venturi needs a new O-ring.  Where can I get one?  I think I will put this one in the new LA-40 and get the appropriate needle from Shtterman.

      The size of the venturi will depend on the size of your spray bar. Like it has been mentioned, if you have an ST needle valve assembly  (which measures .057"in diameter) , and it fit the engine , it has been drilled out for that spray bar. Putting things back to stock will require a late model OS NVA, and it measures .136" or .137", so you need to reduce the size of the spray bar. There is a thread pinned to the top of the section on recommended venturi sizes for various engines. here is a link  :   https://stunthanger.com/smf/engine-set-up-tips/venturi-inside-diameters/
     If you change to the smaller NVA and spray bar, you will need to take care that the side holes in the venturi mount where the spray bar goes through get sealed well, maybe even bushed down if you have the right stuff to do that with. it is handy to have a set of dial calipers and/or a set on number/letter drills to use as a tool to measure the bore of a venturi. Use the smooth shank of the drill bit to check it for fit into the hole. When you find one that is a slip fit, measure with the dial calipers. It takes a while to develop the feel for using this tool if you have never used one before. Watch for Harbor Freight to have their cheap sets of fractional, number, and letter drills on sale to use the shanks as pin gauges.  The shank will be a bit smaller than the indicated size of the drill bit and fit the hole better. You can use the drill bits on wood and plastics and such but don't expect too much performance out of them on steel. Once you have a venturi identified for proper size, scribe or engrave that size on it for convenience the next time you want to know what size it is.
  Type at you later,
  Dan McEntee

LA 46 has a remote needle on a plastic back plate. Leave that alone too?
Kevin.

LA 46 has a remote needle on a plastic back plate. Leave that alone too?
Kevin.

  I would certainly start that way. I have seen no problem at all with either type of rear-needle setup on the OS - the old metal one that is the core of an RC carb, or the integral plastic one. The only problem with the plastic type is that it breaks off if you crash inverted with a profile mount. The clicks are rather large for the 25LA, but manageable.

    I emphasize again - I am not publishing any setup information for the 40 or 46LA. I do not have any. This is just a starting point for experimentation - without the preconceived assumption that you need to cut/grind/drill/modify something as your first step.

    Brett

So I asked this question on FB, but I'll ask again here: I've got a George Aldrich Top Flite Peacemaker (built-up body) with an OS FP 25 on the front.  Flies awesome!  But maybe too fast.  Any thoughts? Some have said replace it with a Fox 35, as the mounting holes are the same. But, I only have space for a 3oz tank in the fuse. Thanks in advance

  Go to longer lines and/or reduce prop size a bit, change the engine to an LA.25. All of those will affect lap times. This is another example of where the OP does not give enough pertinent information such as what prop you are currently using, line length and diameter, and current lap times. Give us something to work with.
  Type at you later,
   Dan McEntee

Christopher,
I wouldn't have thought 5.5 seconds per lap was too fast!
4.7-4.9 on a stunt ship, at my novice level, yes. But I would be thrilled with 5.5 second laps!

Good luck
Craig

/quote/

   Attach a pressure line from the STOCK muffler tap to the suction tank vent. Plug the overflow with an airtight plug. You want it to run on a suction system with pressure, not uniflow with or without pressure.

   Start engine, lean out to a 2-stroke, then slowly lean it out until it is absolutely as fast as it will go, and one click more makes it sag. Then, back off needle until you just get a distinct RPM drop, just a bit off peaked out in a 2-stroke. If you get it rich enough to start misfiring in a 4-stroke, even occasionally, you have gone *much too far*. This is about 5 clicks open from peaked-out lean using the stock OS front needle, about 5 clicks open using the 20FP rear-needle (all-metal on a metal bracket). It is about 3 clicks open from peaked out lean using the stock 25LA rear needle (gray metal needle in a plastic backplate mount). You do not need a tachometer, but it will be 2-300 RPM from peak.

   Launch the airplane and it should get slightly richer-sounding in level flight, and then peak out in the maneuvers. If it peaks out and then sags in the maneuvers, you are too lean, open needle *1* click for the next flight, try again, until it does not sag lean in the maneuvers at any point. If it ever hits a 4-stroke, you are too rich, close the needle one click and try again.

     Brett
   
[/quote/

Does this engine set-up style work for iron piston-and-liner engines like Fox 35 and McCoy?  Albeit with flatter-pitched props and high oil content fuel?  Or are they “ set the motor in a rich 4-stroke, tip the nose up to get it to lean out and call it a day” kind of settings?

C R

C R

Bingo!  Thank you!

C R

Does an Enya .15 (plain-bearing) C/L motor run like a Fox 35 (high-pitch prop, 4-2-4 low RPM) or like the OS? (Flat-pitch prop, high rpm, 2-stroke)?   I think the Enya takes lower oil content, like 22% 50/50 castor synthetic.  Thanks in advance

Thank you, that is helpful! I'm at the point in my life (43 y.o.) where a relatively little amount of time on this forum and facebook Control Line enthusiasts, coupled with once or twice a year meet-ups with New England Stunt Team, have done more for my flying then 25+ years "experimenting" on my own!  (in relative isolation). Thank you! Very much appreciated.  But, I think my Enya looks newer then 1950's/1960's. More like '80's/90's? I've got it mounted on my son's trainer: foam core symmetric airfoil wing (24"?), solid profile fuselage, etc.  I've got another on an Akromaster: flaps, no wheels,


C R