Need some other ideas on an LA 40

My favorite engine just started to misbehave and I can't find the cause(except maybe the weather). It's gotten down in the 60's lately.
It ran fine up until three days ago. Now it runs fine upright, but as soon as you go inverted, maybe 3/4-1 lap, it richens up and starts to misfire. Sometimes so bad it quits. On the ground you can turn the plane over and it never misses a beat.

It's an LA 40 with an enlarged combustion chamber. .262 venturi and OS NVA. 3 bladed 10/4 Master Airscrew. Running a chip muffler.

Things I've tried:
4 oz. Sullivan with two different styles of uniflow vent, free flopping and tied to the clunk
with and without muffler pressure
4.25 oz. GRW chicken hopper tank, with and without muffler pressure
Added a second gasket to the venturi for a positive seal
New Thunderbolt long plug and a new Fox Idle Bar plug
Replaced the plastic backplate(didn't look like it was leaking, but who knows) with a metal one.

Have you tried a new batch of fuel?

LAST EDITED ON Oct-28-04 AT 09:54 PM (CDT)
 
I was recently having all kinds of similar problems on a new broken in OS.25LA. in my Barnstormer. I went thru the same changes you have made to no avail. On another forum it was suggested I check the sealing of the venture and needle valve assy in the crank case. I took out the venture and thought the "O" ring looked to be too small in thickness, so I sealed the venture & "O" ring plus both ends of the needle valve assy with Blue Pematex silicone, problem solved, engine runs great with a variety of props with slight needle adjustments. I did settle on a Zinger 9x5. Another thing to try is close up the uniflow intake vent a bit at a time if the first proceedure fails to make the litte rascel run like a champ.
Jerry

Thank You Jerry. Your post was the winner. I pulled the venturi. The two gaskets were sitting in there, almost concentric, no obvious leaks, but I gooed it up with some silicon gasket goop, reinstalled it and went flying the next day. The engine run problem was gone.

Thanks a bunch. I have not run into this problem before. It probably would have taken me only another 10 flights and two crashes to get it sorted out!!

Despite the new aluminum backplate and new gasket (right?), topic #11050 by OS32 on the Magnum .36 came to mind. Maybe you can pressure test the case, with soapy water on the backplate, screws, etc. Steve

LAST EDITED ON Oct-29-04 AT 01:14 PM (CDT)
 
Didn't switch fuel yet because the same gallon ran fine last week, and runs fine on other engines. So we spent a lot of time trying other things.

Didn't actually goop up the venturi with sealant. I figured squashing two O rings into the gap would do the trick!

Will try that and pressure testing over the weekend maybe. Never had something like this that couldn't be traced to something simple in the fuel system.

>Didn't actually goop up the venturi with sealant. I figured
>squashing two O rings into the gap would do the trick!
>

Phil,

That might be exactly the problem: Two "O" rings where only one is supposed to be used.

Enjoyed your most recent Combat column; actually, I always enjoy it. I honestly thought I had thought of all the good Combat tricks. But running a 25LA with stock muffler just so your opponent can't hear your engine and thus is not sure where your model is?! That is just too good, and I can certainly see where it would work.

For years we've had horsepower races in Combat. Now we'll see a race to have the quietest Combat model at contests? Well, maybe not...

I would like to comment, however, that surely you will be revising and extending your theories as to there being a tuning component to those stock O.S. mufflers. Anxious for the next installment...

LAST EDITED ON Oct-29-04 AT 05:50 PM (CDT)
 
Dan, the "O" rings on the LA series are not as thick as they used to be. I checked my OS 40 fp and thats how I noticed the difference. Putting two of them in may not be the best, I just put on the original and sealent. With the original "O" ring I could slide the N/V assy in and out without pushing down on the ventre to compress the "O" ring, don't believe there was enough sealing there. At least that was my situation with my engines OS.25, .40, .46 LA's. I think on some LA's it is OK, marginal on others and no go on some.
Could be one of the reasons some people have problens with thier LA's.
Jerry

LAST EDITED ON Oct-29-04 AT 04:21 PM (CDT)
 
It may be running slightly rich inverted, not enough to notice when it's warm out. With the drop in temp lately maybe you're flaming out. Have you tried taking out a head gasket or raising the tank?

LAST EDITED ON Oct-29-04 AT 09:26 PM (CDT)
 
Glad you liked the combat column Dan. Good thing somebody reads it. I need the money. Once you figure out how it sounds, the muffled engine runs quite well. Don't think I'll tuned pipe it though, although I did think about getting one of Henry's performance mufflers. The 25 could probably turn a 9/4 prop up around 14K or better with one of those. I refuse to take the bait and debate OS tuned mufflers. If the motor runs, use it.

I did try raising the chicken hopper tank. Didn't do a thing for the run. Funny thing, another identical LA 40 has no problems at all. Neither one has anything more under the head than the stock gasket, so there isn't much to take out. Flaming out seems to capture what is happening nicely.

One thought I had last night in dreamland was to try a larger prop again to load the motor more and heat it up. Maybe it is the 60 deg. weather. But then, that has never been much of a problem with other motors. If they ran at all when it was cold, they ran mostly like they did when it was hot, just with more power.

I have thought about putting a stock head back in and depitching the prop to about 2.5 in. pitch to keep the speed down.

60F. isn't cold, it's still T-shirt weather, and the engine will love it. If one new Thunderbolt R/C Long doesn't work, try another new one. "New" doesn't always equal "good". You might also see about cleaning the gunk out of your chip muffler. Crockpot should do it nicely. If one o-ring doesn't seal the venturi to the case, it's probably the venturi has the spraybar hole mislocated from the shoulder, or the hole oversize. Machined stuff has +/- tolerances on every dimension. They can add up and conspire to defeat us. Steve

Try a K&B-1L glow plug. Thats what I use to wake up a cold natured engine such as a Brodak .40 or a Dbl star .40.

LAST EDITED ON Oct-31-04 AT 11:39 PM (CDT)
 
Shake-up your fuel before fueling. Mr. Lechein, owner of Maxima Oil told me not to use Castor based oil in my trials bikes because it will separate and fall to the bottom of the tank at 50 deg. or lower. This would be a problem at high elevation events in California like Big Bear Lake. I always shake my fuel real good and only have it exposed to atmosphere (humidity) long enough to draw some out. I use an OS #8 plug in all my engines because they always work. Leave the glow driver on and let it build some heat. Permatex Ultra blue in the Chrome tube for the back plate.

>Shake-up your fuel before fueling. Mr. Lechein, owner of
>Maxima Oil told me not to use Castor based oil in my trials
>bikes because it will separate and fall to the bottom of the
>tank at 50 deg. or lower. This would be a problem at high
>elevation events in California like Big Bear Lake. I always
>shake my fuel real good and only have it exposed to
>atmosphere (humidity) long enough to draw some out. I use an
>OS #8 plug in all my engines because they always work. Leave
>the glow driver on and let it build some heat. Permatex
>Ultra blue in the Chrome tube for the back plate.

Steve,

Your suggestion is a good one and I sometimes shake my fuel jug prior to use.

However, I always feel foolish when doing so. Especially when I have just driven a couple hundred miles, entire contents of the van subjected to every single jolt and jostle during the trip.

I do not recall castor oil falling out of solution with model fuel of less than 45% nitro content, and certainly never had pre-mix separate back when I was riding two-stroke dirt bikes. Even when we were dumb enough to go riding in the snow...

mr. lechien as in ron "the machine" lechien? i always wondered what happened to him! apparently old mx guys go on to sell oil, grips, goggles, etc. now, if i can only locate "bad brad" lackey and jammin' jimmy weinert......

>mr. lechien as in ron "the machine" lechien? i always
>wondered what happened to him! apparently old mx guys go on
>to sell oil, grips, goggles, etc. now, if i can only locate
>"bad brad" lackey and jammin' jimmy weinert......

"The Machine" is still active in Motocross, although I cannot remember with which team.

Brad Lackey is pretty much inactive. If you really want to know, Jim Pomeroy, I have been told, has semi-retired back to the Yakima Valley here in Washington state, Yakima being where I was raised, purchasing a couple motorcycles from father Don Pomeroy. Jim would surely know of Lackey's whereabouts, they were great buddies back when racing professionally.

Mr. Lechien is Ron's dad. I believe his name is Mike. When he told me about the Maxima 527(Castor) oil separating at below 50 Deg. F. We were of course talking about gasoline. The issue was the ambient temp. Shaking pre-mix fuel, gas or methanol before use, is just common sense. That's my story and I'm stickin' to it. As for Da' Dirt, your poor ol'worn out FP 20 probably needs Aunt Jemima to build compression. Hehehe.

LAST EDITED ON Nov-04-04 AT 00:02 AM (CDT)
 
Even when we were dumb enough to go riding in
>the snow...
>Dan

Yeah, Your not alone!!!!

Me too! I only did it once. It was a Memorial Day weekend, out near Goldbar, at Reiter's Road area, snowing like mad, about '75. My buddy and I both took our wives and gave them a ride up the mountain and back. Yeah, leaning the wrong direction on corners, and all the usual helpful techniques. Neither one of us fell down, which was an display of amazing skill. Neither wife fell (or was pushed) off the bike, either. They also never wanted to go again. Steve

LAST EDITED ON Nov-05-04 AT 03:59 PM (CDT)
 
Actually, I ended up riding in snow every single spring for years and years.

We'd get all pumped over weather at lower altitudes, haul the bikes to the mountains in trailers hooked to semi-nasty Jeeps. As a lot of our riding was on logging roads that early in the year, we would frequently exit a corner bathed in sunshine, pin it just to feel the really good traction...and run into a snow bank on shadowed side of the hill.

Sometimes you could ride over them, sometimes you had to push. And sometimes you'd discover there was a small stream hollowing out the snow bank from underneath.

Once this got tiresome, it was great sport in the Yakima Valley to see who could get a Jeep first to Darlin Mountain look-out and then down into Kilickitat Meadows. Details not now, but this involved blasting snow banks. Getting stuck. Being rammed from behind. Rammer being rammed. Our limit was three stuck Jeeps, fourth in line already being tied to third with really stout chain. In fact, all the Jeeps, in nasty going, would be tied together.

Thus last guy in line would back up, snatch the one in front of him and so on until we were all free.

Repeat. Again and again.

My group was never first-in or last-out to either site, but we tried.

Last out? Oh yeah, and it wasn't for girlie guys. As there is quite the climb up and out of Klickitat Meadows, the idea was to be in the meadows during a good snow storm, and then climb out *just before* the road became impassable.

Every year the first guys in come across Jeeps that have been there the whole winter, abandoned months ago. Approved procedure is to just shove them off the narrow road, although it is bad form to see them rolled onto their top. Loss of vital fluids, don't you know...

I had a casual friend in high school who was two years ahead of me. About 1962 he had to buy a second Jeep because his was in the mountains for the winter. Next year he suffered the exact same fate. But already had a spare, so didn't much care.

Phil,

I noticed in another thread that you may have discovered source of the problem which started this thread, even though Greg, Steve and I converted it to dirt bikes and Jeeps in the snow.

Uh, y'all aren't thinking about leaving this hanging, are ya? We want to know, 1) If you screwed up; 2) How you screwed up; 3) That it was definitely your fault; 4) The suggested fix.

Not for me, you understand, all of my Stunt equipment being perfectly prepped. But Steve and Greg could probably benefit from your insights, especially items 1) through 3).

See post #15.

>See post #15.

Ty,

Oh. Sorry.

But did you notice how Phil buried it so as not to address my innocent questions?