Glow Engines Discuss RC glow engines

O.S. LA40 carb

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Old 02-24-2010, 06:36 AM
  #1
willig10
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Default O.S. LA40 carb

Guys. I just bought a brand new O.S. LA40. Looking at the carb the throttle plate looks to be smaller than the venturi hole (i.e. restrictive). As you know this has the remote needle valve on the back of the engine.

What I am looking for and my question is this:

1. Is there a bolt on carb that can replace the carb currently on the engine? In other words remove the carb and rear needle valve.

2. Has anyone done this? Looking for real options not opinions here.

Thanks
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Old 02-24-2010, 09:49 AM
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Default RE: O.S. LA40 carb

There are after market carbs, notably Kavan (www.mecoa.com)and Perry (www.perrypumps.com). But the carb on the LA 40 is just fine. What's wrong with a remote needle valve? You can unbolt it from the back of the engine and mount it on your airplane if you want. Remote needle valves are safer in that they keep your fingers well away from the prop. And the needle valve does the same job whether it is up front or in the back of the engine.

Cheers,

Chip
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Old 02-24-2010, 10:40 AM
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Default RE: O.S. LA40 carb

Hi!
Why replace a perfectly working carb????
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Old 02-24-2010, 11:02 AM
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Default RE: O.S. LA40 carb

As stated earlier. The throttle plate is restricted as looking down the venturi. What I am looking for is a tad bit more power. In other words is there a carb that when fitted to the engine will make it look like a regular .40 size like an FS etc. I am not new to RC been in it for 20+ years. I understand your concern for newbies. I know where my fingers are when I am adjusting a needle valve.

Glenn
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Old 02-24-2010, 11:06 AM
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Default RE: O.S. LA40 carb

Hi Willig, you can change the carb by an OS 3A carb. This carb was from the 35_40 FP, and yeas, it has a frontal needle. Also you could change the plastic backplate from one of the 40 FP also. Many C/l flyers in my area does this.The venturi in the carb on the 40 LA is restrictive in order to give a steadier run and an overall good running.
Regards

Carlo
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Old 02-24-2010, 11:09 AM
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Default RE: O.S. LA40 carb

Quote:
What I am looking for is a tad bit more power.
For the price of another carb, you could almost buy a more powerful engine.
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Old 02-24-2010, 01:59 PM
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Default RE: O.S. LA40 carb

Thanks carlo. I dont understand why it is when you ask a question you get answers to everything but your question. I will go and see if I can find the backplate and the carb at a LHS.

Glenn
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Old 02-24-2010, 03:16 PM
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Default RE: O.S. LA40 carb

I have several LA and FP 40s and last time i checked, the LA carb actually has a bigger choke (hole in the barrel) than the Fp carb, so the Fp carb won't do you any good. Unless OS has made a change.....my FP carb barrels measure around .202 to .209, the LA is around .230.

For WOT use for combat, we would enlarge the barrel to as much as .250. Drilling the barrel is a BEAR, it is hard and you either have to anneal it, or use a carbide bit.

The mismatch in size between the carb body and the barrel is key to making an airbleed-style carb work, if you don't have that mismatch, your idle and midrange quality will suffer greatly. I can't explain it fully, i read an article about it years ago and it was a revelation. All the carbs I had enlarged were only good for WOT and would not throttle well. Then I read the article, which I believe (long time ago, memory shot) that the carb barrel area has to be around 18% less than the carb body area- it might even be more. A good way to find out would be to measure your LA and do the math. Anyway, when i first enlarged my carbs, I drilled them all straight thru. After reading the article, i further enlarged the carb bodies, relative to the barrels, and the throttlability was mostly restored, although of course with the much larger choke area, fuel draw goes down and that usually means the midrange gets fatter. you can enlarge the airbleed hole but that only goes so far.

The best way to get more power out of an LA is to remove the muffler baffle, ream out the tailpipe to about .250", and experiment with removing the head shim (depending on prop and nitro level, this may or may not help- on my engines it almost always did). I gave up on enlarging the carb- it's a definite performance boost but a real hassle and in general the engine is less user-friendly after you're done.

For my FPs, if I want more power, I use the LA carb! Another good carb but no longer in production was the one from the (old, plain bearing) Tower 40, which was an FP clone.
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Old 02-24-2010, 04:31 PM
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Default RE: O.S. LA40 carb

Hi!
You will not see any rpm change by mounting a bigger carb. Remember this is a beginner engine with very tame exhaust timing!
But! If you really want more power the best way of doing it is mounting a tuned pipe; Either a magic muffler or a long tuned pipe.
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Old 02-24-2010, 05:04 PM
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Default RE: O.S. LA40 carb

Ok now were getting somewhere. This is good info. Thanks. Appreciate all your responses. I did not know the FP/FS series carbs were actually smaller than the LA series engines. Well let's see how this engine performs on a Hangar 9 arrow trainer soon. I have 3 airplanes and I like to fly the trainer just to keep me tuned. I also have an RV-8 with an O.S. Max 75AX. I am currently building a Hangar 9 Taylorcraft 20cc which will be powered by a Zenoah G-26ei. Thanks and keep the info coming.

Glenn
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Old 02-24-2010, 05:36 PM
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Default RE: O.S. LA40 carb


Quote:
ORIGINAL: willig10

Well let's see how this engine performs on a Hangar 9 arrow trainer soon.

Glenn
The .40LA is the weakest performing .40 on the market, it is smooth running, reliable, lightweight, thrifty on fuel, but not powerful by any standard. If that is what you need, it is a good engine.
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Old 02-25-2010, 01:38 PM
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Default RE: O.S. LA40 carb

I put a 46 la throttle barrel in a 40 la carb it was a little bigger
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Old 02-25-2010, 03:39 PM
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Default RE: O.S. LA40 carb

Another option that will cost you next to nothing is to polish the throat of the carb. Both the top and bottom of the venturi. It is an old Hot Rodders trick to take a small carb and make it flow better by a simple polish job. I do not know how rough your carb is so it would be your judgement.
Iuse Mothers mag polish on little jobs like this, be sure to clean up well afterwards.
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Old 02-25-2010, 04:16 PM
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Default RE: O.S. LA40 carb


Quote:
ORIGINAL: willig10

Thanks carlo. I dont understand why it is when you ask a question you get answers to everything but your question. I will go and see if I can find the backplate and the carb at a LHS.

Glenn
Nobody's trying to be a dick.. forums are electronic round table conversations. To a lot of folks it sounds like you are about to waste money trying to get blood out of a stone, and they are trying to be helpful by asking something to the effect of "why bother spending time and money on something that seems like it is not worth it"? You can only pile so much jam on a slice of stale bread. As an example a new TT Pro .46 is just over 90 bucks. A new carb and backplate is how much?

MJD




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Old 02-25-2010, 04:26 PM
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Default RE: O.S. LA40 carb

I can see where the original poster is coming from, Iwould love to have an engine the size and weight of an OS40LA with the power of a .46.
But most feel it is a waste of time.
Please dont take it personally.
Do not be discouraged either as Ihave taken engines with mediocre power and made to run very nicely.
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Old 02-25-2010, 10:16 PM
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Default RE: O.S. LA40 carb

I wasn't trying to be mean. When I posted the question about the carb, I just wanted to know if there was a bolt on alternative that would provide just a tad bit more power. I am not concerned about cost. I fully realize how much engines are on the market. I can go and buy one if needed. I just am curious, as this is the first engine that I have seen with the throttle body noticeably smaller that the venturi when at full throttle setting. Sorry if I offended anyone that was not my intention. Please keep coming with any and all ideas/suggestions you have.

Regards
Glenn
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Old 02-25-2010, 11:56 PM
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Default RE: O.S. LA40 carb

Ok guys the OS40 series are as we know (and some of you have pointed out are not noted for being powerhouses), They are however very user friendly, reliable,
and preform as advertised , they are missing the 2 schnuerle side ports of their more expensive OS brothers, this of course cuts the cost of making the engine
I do not think moding or changing the Carb will make a big difference since the amount of fuel charge mixture is thus restricted.
The one thing that does really increase their power is converting them to diesel ( Davis heads) they only burn about half as much fuel as glow
Hobbsy has an LA46 that turns a graupner 12x7 at 9100, John Pavlick did a review of the 46 conversion in Dec08 of fly RC
being now a diesel they do use less fuel hence the intake porting is out of the loop
I know this is the glow forum but a quick review on the diesel forum will really show how good these engines can really do
can you compare them to say the AX46 in power as glow no way. again the oily rag group likes them
Either way they are still good engines martin
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Old 02-26-2010, 11:47 AM
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Default RE: O.S. LA40 carb

Humm. Want more power - go to bigger engine. An LA 46 is a bored out LA 40, more cubes ergo more power, same essential performance. Perhaps that is why the LA forty is no longer manufactured, eh? And if that is not enough power, go to a Tower Hobbies 46/GMS47/TT46 Pro/OS 46FX or AX. That kinda takes you from the lowest cost to the highest cost higher performance 40 series engines. Of course you can go to a Rossi or a Jett then you can really humm along. I left out Supre Tiger but they to fit in that category.

The point being it is not worth it to fool around with bigger carbs when the engine timing and ports are not present to increase the power.

And do keep your fingers safe.

Cheers,

Chip
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Old 02-26-2010, 02:46 PM
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Default RE: O.S. LA40 carb

The classic post on here for many years has been the guy wanting to know how to adjust his tuned pipe on his LA-40 so it runs like the big engines he sees at the field.

The tuned pipe costs more than a LA 40.

They don't seem to respond to tuning modifications all that well. The hole up the center of the crank is just too small and they have busings for bearings.
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Old 02-26-2010, 03:53 PM
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Default RE: O.S. LA40 carb

understood. I will see how this engine does with the Hangar 9 arrow. If it wont pull it I will install a bigger engine. I just thought there was a carb that would help this engine out. I was not aware that it did not have the schnerlle porting. Oh well I will see how it does soon. Sure is pretty though.

Thanks all
Glenn
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Old 02-26-2010, 04:16 PM
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Default RE: O.S. LA40 carb

It does have schnurle ports, it just doesn't have the boost port.

The factors are the timing and that the size of the passages are set up for it to be a sport engine for a trainer type plane.
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Old 02-26-2010, 04:41 PM
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Default RE: O.S. LA40 carb


Quote:
ORIGINAL: w8ye

It does have schnurle ports, it just doesn't have the boost port.

The factors are the timing and that the size of the passages are set up for it to be a sport engine for a trainer type plane.

A mousse can pipe (home made semi resonant exhaust system) will reduce the overall weight of the muffler/engine combination and it will give the anemic .40LA a mild boost in power, while being substantially quieter than the stock muffler. Nitromethane is another way to increase the horsepower of any IC engine, even the lowly OS .40LA. I have both the .40 and the .46 LA. I can't see any significant difference in power between the two.

There are lots of articles and information on the net about constructing and tuning the mousse can muffler exhaust system. Look for "Bob Adkins - mousse can muffler/pipe".


Ed Cregger
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Old 02-26-2010, 05:09 PM
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Default RE: O.S. LA40 carb

There was a guy at the flying field where BLW flies (I used to fly there) that had a Diamond Dust delta that he had bought from someone with a Norvell 25. He removed the 25 and put a OS LA 40 on the plane with a 8-4 prop. Sounded pretty good.

He kept making low flyby's and eventually hit a fire ant mound. The only thing left was the LA 40.
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Old 02-27-2010, 01:30 PM
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Default RE: O.S. LA40 carb

What does it matter if the engine has only bushings and not roller bearings? The bushing engine has the crank floating on an "oil bearing". Just like your car engine.
Ishut up now, I hear the flames building.
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Old 02-27-2010, 04:13 PM
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Default RE: O.S. LA40 carb


Quote:
ORIGINAL: jeffie8696

What does it matter if the engine has only bushings and not roller bearings? The bushing engine has the crank floating on an ''oil bearing''. Just like your car engine.
I shut up now, I hear the flames building.
True but you auto has a pressure oil system and the oil is forced into the cap bearings. The oil is captured in the bottom of the crankcase and recirculated again and again nder pressure.

The crank in the LA 40 relies on pressure to, from the crankcase and it is from the piston travelling down. That down travel also forces the fuel/air mixture up the ports to the combustion chambers. So oil has to get there first before it rides on the lube.

Cheers,

Chip
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