LA-46 Unrest

All,

I’ve been running a new LA-46 in my 48 ounce Time Machine 50. As of yesterday I have 20 flights on this combination. I’ve been very happy so far with this combination, but it seems that trouble may be looming. While everybody else in the free world seems to get perfect runs with their LA, mine seems to be beginning to exhibit an almost FP style runaway. Twice in the last five flights I have had the engine surge to a flat out two stroke, stay there for a maneuver or two and the level laps between, then drop back into a 4-2-4 for the rest of the flight. The first incident of this occurred in cold conditions (40 deg) with the air temp rapidly cooling as the sun set. The engine was a bit leaner than wanted at takeoff as I failed to adjust for the very rapidly cooling conditions. The engine surged into a howling two at takeoff and stayed there untill after the inside rounds, when it dropped back and stayed in a fast 4-2-4 for the rest of the flight. Yesterday, in 68 degree temps, I had a two good runs, then I tried needling down maybe a 16th turn on the ST nva to help with the rapidly worsening wind conditions. I noticed that it took two laps after takeoff for the engine to drop down to a four run, and it performed nominally until the overheads, when it surged to the same howling two and stayed there until 8 laps after the clover, this time lean enough in the two for the engine to fade a bit in the vertical legs of the clover. To me this has All the earmarks of an unmodified FP 40 starting to exhibit the runaway you see when they have broken in, but all I’ve ever heard about the LA is how great they run out of the box. What gives? Is mine overcompressed or not timed right for some reason?

Here’s the setup details for the curious: LA-46 with .285 venturi, ST spraybar and needle. Sig 003 plug. Fuel is Fox Superfuel (I wanted this for breakin, them maybe try 10/22, but the engine ran so well for me on superfuel I’ve kept using it till now) Muffler is Big Art tube muffler. Prop is rev-up 12x5 wide, under normal conditions it seems to turn this with authority without acting overloaded. Uniflo vented GRW tank, uniflo vent directed into airstream with no pressure or restrictors. I have not tached this setup, my preferred run is in a very fast four, this engine has a very indistinct break but I like that sort of run, typically it will slip into a wet two down wind and just barely drop back into the four upwind. Its very noticeable when the runaway hits as opposed to the two stroke in the break.

What gives? Is my engine turning into a lemon? Should I try a head shim? .265 venturi? Prop??

Check your backplate. I have one of these engines that had run well for many flights, then began running lean in flight. The backplate was leaking.

>Check your backplate. I have one of these engines that had
>run well for many flights, then began running lean in
>flight. The backplate was leaking.

I was writing while you were posting, Don, but, yup, we both thought of the same thing.

>
>(snip) Here’s the setup details for the curious:
>LA-46 with .285 venturi, ST spraybar and needle.
>Sig 003 plug. Fuel is Fox Superfuel (snip)
>
>What gives? Is my engine turning into a lemon?
>Should I try a head shim? .265 venturi? Prop??
>
>
>Steve

Steve, you already have a .265 venturi. I know, you said .285, but you put an ST spraybar in it which chokes it down to the equivilent of the .265. What I would suggest is going to a larger venturi. OS supplies a .257 venturi (too large) on the 20 and 25 FP. Then they originally supplied a .265 venturi on the .46 (too small). They have since (wisely) increased the size on the .46 LA and I think you should, too. Even without the boost port blocked you could take the venturi up to a .280 with the OS needle. That is a .300 equivilent with the ST. And with the boost port blocked, you can go even larger. Try a couple of different ones, or bore it out progressively to see what happens. If it gets too big (for your taste) you can replace it with a slightly smaller one.

Also remember, there are manufacturer's tolerances on these (and all mass produced) engines, so, without blueprinting it, yours could run slightly different from someone else's even with the same set-up. This is something we won't know.

Also, I would suggest going to fuel with a bit less oil in it. And make sure the back plate is tight and not leaking. That will cause what you are experiencing, too. Dump the plastic back plate and go to a metal one.

I forgot about the backplate issues with the LA. Since I have a bunch of spare metal ones sitting around, it can't hurt to try that first. I'd planned to switch to 22% lube but was thinking it would make the runaways worse, not better. But there is no substitute for testing it out and seeing what happens, I just need some better weather up here. Thanks for the tips so far....

Just as a reference point,

I started with a 293 venturi and ST needle in my LA 46 and it was a tad too large for consistent runs. A Bru-Line air filter fixed it so it wasn't very far off. Might start with something a bit smaller and work your way up.

>Just as a reference point,
>
>I started with a 293 venturi and ST needle in my LA 46 and
>it was a tad too large for consistent runs. A Bru-Line air
>filter fixed it so it wasn't very far off. Might start with
>something a bit smaller and work your way up.
>
>Bob

Interesting on the venturi. YOu say a .293 with a ST needle is too big??? That is the equivilent of a .273 with the stock OS. And we are talking about a 46 here! I would consider a .273 marginally low at best. A .281 (with the OS needle) would be better, which would be the equivilent of a .301 with the ST needle. It would sound to me like you are trying to run it too much like a Fox, rather than get the power out of it that it is capable of.

Oh, and by the way, the choke area of your set-up is .022. That is before you put the filter on it. Do you know what the choke area of a stock Fox 35 is? .022

Don't know, just reporting what worked with my box stock LA on a Buccaneer 740 running 5-22 GMA fuel. The fuel tank wasn't large enough but if it was, this set up would do the pattern with confidence on 65 foot lines without ever breaking into a 2 stroke. The airplane and engine is now in the hands of one of our up and coming teenagers or I would weigh it and report the weight.

Maybe we have denser air here in Oklahoma, two of our club members are running 228 venturies with OS needles in FP-20's on Flight Streaks and they both run fantabolus. You have also said this is to small for the 20. I really don't know, I just use what works.

>(snip)Maybe we have denser air here in Oklahoma, two of our club
>members are running 228 venturies with OS needles in FP-20's
>on Flight Streaks and they both run fantabolus. You have
>also said this is to small for the 20. I really don't know,
>I just use what works.

With the OS needle the .228 venturi is about right for the 20FP. Use a .238 fora .25. Stock on these is .257. Put an St needle in these and it gets a lot closer.

>
>>(snip)Maybe we have denser air here in Oklahoma, two of our club
>>members are running 228 venturies with OS needles in FP-20's
>>on Flight Streaks and they both run fantabolus. You have
>>also said this is to small for the 20. I really don't know,
>>I just use what works.
>
>With the OS needle the .228 venturi is about right for the
>20FP. Use a .238 fora .25. Stock on these is .257. Put an
>St needle in these and it gets a lot closer.

My 20FPs run great with the stock setup. The 25, on the other hand, seems to need something slightly smaller, particularly in high density altitudes. The ST needle in the stock venturi is smaller than required, although it runs fine that way.

>

>
>. Even without the boost port blocked???

Hi Len,

I thought the LA .46 didn't have a boost port!

I got a Tower .40 backpalte and venturi for mine and an OS
.40FP needle. What should I bore the venturi out to?? .275-280?
Just curious about what give best performance.

Thanks!

>>
>
>>
>>. Even without the boost port blocked???
>
>Hi Len,
>
>I thought the LA .46 didn't have a boost port!
>
>I got a Tower .40 backpalte and venturi for mine and an OS
>.40FP needle. What should I bore the venturi out to??
>.275-280?
>Just curious about what give best performance.
>
>Thanks!
>
>
>Jim Pollock

What I meant was, even if it didn't have the boost port blocked, I would take it that high. With the boost port blocked, you can go even higher because you have greater crankcase compression.

On the LA 46, if you are using the OS needle, I wouldn't be afraid to take it as high at .290 or .295. Ironically, OS is now supplying the stock engines with a .295 venturi. And to think, they started with a .265, the same as they used on the .35 FP.

>>>
>>
>>>
>>>. Even without the boost port blocked???
>>
>>Hi Len,
>>
>>I thought the LA .46 didn't have a boost port!
>>
>>I got a Tower .40 backpalte and venturi for mine and an OS
>>.40FP needle. What should I bore the venturi out to??
>>.275-280?
>>Just curious about what give best performance.
>>
>>Thanks!
>>
>>
>>Jim Pollock
>
>What I meant was, even if it didn't have the boost port
>blocked, I would take it that high. With the boost port
>blocked, you can go even higher because you have greater
>crankcase compression.
>
>On the LA 46, if you are using the OS needle, I wouldn't be
>afraid to take it as high at .290 or .295. Ironically, OS
>is now supplying the stock engines with a .295 venturi. And
>to think, they started with a .265, the same as they used on
>the .35 FP.

Ready for this. At the hobby shop the other day I took out a NEW 46LA control line version..The verturi was .303? Has anyone come up with that one yet?

>Ready for this. At the hobby shop the other day I took out a
>NEW 46LA control line version..The verturi was .303? Has
>anyone come up with that one yet?

Ho boy! Does anyone know what OS is doing these days? And then there are people who keep insisting "Just run it as it comes out of the box." It is getting so one needs to measure up the whole engine and then decide which version he wishes to copy.

Len, Scott

I think I will just stick with a .281. I'n not going to ask mine to pull a 2,000 car freight train!

Leonard
The guys that flyem straight out of the box, like me gotem befor any crazy changes had taken place.

By box stock LA46 is a horse on 5/29 GMA fuel. This engine does not care if you put a 13/5 or a 12/5 on it. It breaks perfectly every time but it is a fuel hog.I am flying just the way it came.

What I am getting at is, did you get yours with a .265 venturi, .272 venturi, .278 venturi, .281 venturi, .295 venturi, or the latest .303? That is over a 50% increase in choke area from the smallest (earliest) until now. That has got to make a wild variation in how one person's engine will run compared to another's. We move venturi sizes by two or three thousandths. Here we have a near 40 thousandths difference. And that doesn't take into account the differences in deck height, etc., that will also affect the run.

Hi Jim, Each set up appears to be unique! But do use a tapered reamer and NOT DRILLS! The reamer lets you do a tiny bit at a time and there-fore see the incremental improvement a little at a time. Phil Spillman

My guess is also a loose backplate. My LA 46 runs very well x about 3 years right out of the box but the backplate seems to get loose a couple times a summer and you can tell when it happens because the run gets unpredictable. I bought one of the Tower 40 covers to replace it but have not as yet because I am still using the remote needle. Also if you can post a picture of your Time Machine. I am building the 60 sized version.

Thanks

Rick,

I'll see what I can do about the pictures. I've got some killer jpgs of it Willis Swindell took last week with his digital camera, but I've never taken the time to figure out how to post.

Out of throughness I'll replace the backplate on my LA, but I'm not sure if its the problem or not at this point. I just have the feeling something else is going on, especially since the two runaways to date have been when I took off with a setting a bit leaner than I wanted, and flights with a perfect needle have been a-ok. Right now it just seems like the engine is not as idiot proof with prop or needle as I had supposed it to be. I'll need more flights to be really sure I have a problem or not, but by posting this issue early, it gives me more ammunition to troubleshoot with when I do get more time at the field. Thanks to all who commented, and thanks for the tips about the ever increasing venturi sizes. I have four LA-46s purchased over the last two years. Wonder how many venturi sizes I've got.......!

Here is a picture of Steve and his Time Machine 50 powered by the LA 46. Photo by Willis Swindell.

I have had the same problem with this engine. I was running Rev-up 11x6 and 11x5 props. The real trick most of the guys here in the Northwest are using,is the fuel and prop combo. I am using .285 venturi with OS NVA, and now use Powermaster 10/22 and APC 11.5x4 prop. These props are ugly but made with a fine degree of knowledge. I think using synthetic oil in the fuel is the best bet for the LA series engines. I had total frustration till I switched to this combo. I also switched to a metal backplate. Jim J..... Here is an email from Derick Pickard.... The transfer and bi-pass ports are the same thing. It's just that I'm an ex-UK two stroke engineer and use the UK name (transfer). these are the two little ports which transfer the incoming gas from the bottom of the engine (crankcase volume) up into the combustion chamber so bi-passing the piston. They are either side of the single exhaust port which exits to atmosphere.
You can use a Dremel to grind the liner or a file. Certainly a fine file is best as can be used on the top of the piston. And by all means use a scriber to mark the position of the two transfer ports in relation to the piston top. And when notching the top of the piston in two places to open the transfer ports early, it's a good idea to be a little wider with those notches.
You must fit the extra head shim(s) and I'd advise only 20% castor oil and do try 5% nitro if your engine is too lively.
If all this is too hard, simply send the engine to a specialist like Tom Dixon. also.......Jim
The piston notches must be the same width (curved circumferential distance) as each transfer port to ensure a good match, be as low as desired (1mm or whatever down from the top of the piston) and reach towards the centre of the piston top by 2 or 3 mm to give the incoming gas "no sudden hill to climb". And on that last bad expression I'll just say good luck.
Good luck
Derek Pickard This is reference to the recent article in Stunt News

I, too, was having some inconsistent runs and switched to an all-synth fuel (5 percent Rich's) because I was caught at the field with only my Stalker fuel. Four great runs until I tried to be a farmer and plow the field.

Steve,
I had some initial problems with my LA46, as far as running away and inconsistent runs. Even though there was nothing apparently wrong with my uniflow tank I changed to a different tank and that fixed most of the problems. The other thing that really made a big difference was to run a Bolly 3 blade prop, 11 in. 4.5 pitch, and one added head shim. Now it runs great.
Also make sure to check the collet on the NVA, that is is tight, replace fuel filters, check lines for pin holes or cracks, clean out the spray bar, and make sure the tank is not vibrating.
And yes, replacing the backplate is a good idea too.
Good luck,
Brian

Hey Brian, where are you getting your head shims from???

a 0.010 shim I take it?

Steve,
I got mine at Tower
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCM65&P=Z

.013 thick.
They have discount shipping for the LA parts.
Brian

Some ideas to consider. 1)Be suspect of the plastic backplate. I always thought the safe thing to do was to replace it before running the engine. Also replace the screws with a set for a Magnum XL .25 > .36 (maybe larger). Socket heads are better, give better feel of the torque you are applying. No leaks!

2)I'm not convinced that my dial calipers will reach deep enough into the stock venturi to get a true reading. Best to use a drill for a plug gauge, then caliper or mike the drill.

3)From what little I ran my .46LA on a 4-2-4 run, it was on 10-22GMA, a Big Art tube muffler, and I tried a variety of props. Ones that I liked were the 11-6EW RU, and the 12-5 APC. My impression was that both were too much load, but the 12-5 APC, trimmed to 11.5" might be just the ticket. As the same props work well on my ST G.51, and as it seems to like the Graupner 11-6, that might be another prop to test. I like to be able to replace props without going to eB*y or waiting for an estate sale. Bottomline, I think your 12-5W Rev-Up is too much prop.

4)When Jimmy (Johnson) got his .46LA, I suggested 10-29 GMA would work fine (and he had some), but apparently this was bad information for a 4-2-4 run. It worked fine for my 2-2-2 Mac's Muffler setup, not so for Jim's. One of those stunt mysteries. Steve

Hi Steve, You may want to try ST.45 or St.51(GS) gaskets as well from Tower. These are thinner than OS' and would you believe...CHEAPER! Oh and they fit too!

Thanks for the shim info guys! If a ST 51 shim fits I bet I can scrounge one at KOI next week and have it on hand if I need it.

What I really need is a good hot July day where I can put up fifteen flights back to back, where each time I land Willis comes out with a different prop or other adjustment to try and Tate hides in the shade from the tree and hollers out good natured "suggestions" and other various imprecations. Those sessions are good for sorting stuff out.

BTW, thanks for posting the picture John. I'd hoped for the more heroic inverted flight shot which prevented my ugly mug from being displayed, but the pic you chose does at least show what the plane looks like!

All,

This past weekend, at the KOI, the immediate cause of the runaway problem was identified and repaired. The anti-plastic backplate guys win the prize.

I had brought the Time Machine 50 to KOI as a backup, but a structural failure in my Gieseke Nobler's wing in friday practice forced me to ground the Nobler and pull out the Time Machine for the rest of practice, where, on cue, the motor promptly ran away worse than ever. Since nobody had any head shims I could mooch on short notice, I figured I was doomed for the weekend. But Kent Tysor's sharp eyes spotted oil weeping past the backplate, and he suggested yanking the motor and changing the backplate in the field. Although short of head shims, metal backplates were one thing I remembered to bring and the metal backplate went in. Instant fix, although I was astonished on how far I had to turn the needle in to get back my normal RPM. Having barely practiced the plane I was not competitive for the win in Advanced, but I didn't totally embarrass myself, either. The plastic job must have started leaking by flight 10 or so and very gradually worsened each flight, while I kept opening the needle bit by bit, but to no avail.
The backplate screws seemed tight, except one that was not as tight as the others by maybe 1/16th turn. Even that screw was nowhere near what I would call "loose", though. With the new metal plate on, the engine ran perfectly from beginning to end of the tank at whatever speed I set. While originally I had been with those out there that said give the plastic backplate a chance, based on this experience, I join those that say chuck the plastic backplates into the bin and beg, borrow or steal a metal one.
Thanks to all who posted, glad to report I'm back to being very happy with the LA 46!

Steve,

That's why I got a Tower .40 backplate for mine and plan to install it and the .135 needle and .280 venturi before I even attempt to run mine any