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46 LA fuel?

Old 04-30-2008, 03:58 PM
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Default 46 LA fuel?

Wha t nitro content is best for a 46 LA? I ran my old 25 os the other day and it ran SO much better than my 46. I am currently running 15 nitro.. My 25 seemed to idle smoother and transition to full speed MUCH better than the 46.. Could this be from the fuel?
Old 04-30-2008, 04:38 PM
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Default RE: 46 LA fuel?

10% or 15% Nitro is usually ideal for the .46 LA. They're not wildly sensitive to nitro content, but they can be sensitive to oil content. 18% to 20% total oil content is fine, and most sport fuels contain 18% oil. Plain bearing engines like the .46 LA will fly best with castor oil rather than synthetic oil for lubrication.

Castor oil is thicker than most synthetic oils, and castor lubrication will help "float" the crank shaft inside of the bushings for smoother performance. Castor oil can also help seal up tiny leaks and gaps in the machining of the engine resulting in better compression and more power.

Running a plain bearing engine like the .46 LA on 100% synthetic lubrication fuel won't necessarily hurt the engine, but it won't run as strongly or as smoothly as it could. As a minimum, fuel with an 80/20 synthetic/castor lubrication content would be better, and 50/50 synthetic/castor oil better yet. If you can't find 50/50 fuel and you have to run your .46 LA with either 100% synthetic or 80/20 synth/castor blend lubrication, just buy castor oil from your local hobby store or pharmacy and add about 4 ounces per gallon of fuel.

Synthetic oils are less expensive than castor oil, so most sport fuel is sold with synthetic lubricants because profit margins are better. Sig Manufacturing still offers 50/50 synth/castor and 100% castor sport fuels, but it's not often carried by many hobby stores. 100% castor lubrication would actually be ideal for most 2-stroke engines, but castor oil in large quantities can contribute to carbon buildup on the valve assemblies in 4-stroke engines. Even Saito 4-strokes can be normally operated with 80/20 synth/castor fuel, however.

A properly tuned .46 LA with 10% or 15% nitro and plenty of castor oil lubrication will run for a decade or longer and supply plenty of power. Feed it the right lubrication and work at tuning the air-bleed idle setting and high end needle as best you can, and you will love this engine!

Based on your description of rough idling and poor transition, I think you need to work at adjusting the air-bleed screw on your carburator in particular. Turning out the screw to allow more air in will lean it out. You can use the "pinch test" while your engine is idling to confirm that it's running rich at idle before attempting any adjustments.

With the engine running at idle, pinch the fuel line between the remote needle valve and the carburator shut. Ideally, the engine should speed up for a second or two then die. If the engine runs normally for a few seconds and then speeds up and dies, it's running too rich at idle. If it dies almost instantly without speeding up or while only speeding up for a split second, the idle setting is too lean.

If you turn the air-bleed idle screw all of the way open and the low end is still too rich. You can use a very small drill bit to drill out the air bleed hole in the carburator to the next bigger size. Engine gurus say this is sometimes necessary to get an air bleed carburator to idle and transition in an optimal fashion.
Old 04-30-2008, 05:01 PM
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Default RE: 46 LA fuel?

10% - 15% nitro is fine for an LA. Is this a new engine? If so, it may need some more break-in. I've run the .40 LA and FP and both are good runners and idled smooth with no problems on 5%, 10%, 12% & 15% fuel.

Old 04-30-2008, 05:43 PM
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Default RE: 46 LA fuel?

15% nitro runs great in my .40 LA
Old 04-30-2008, 06:15 PM
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Default RE: 46 LA fuel?

Well it can and it cant. It could either be you engine settings (which from the sound of it is not your situation), or yes it can be the nitro in the fuel. Hey if it runs better then use it obviously.
Old 04-30-2008, 09:12 PM
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Default RE: 46 LA fuel?

I have had A bunch of those engines and have run everything from 5% to 15%. I run Power Master 15% on most everything so that's what the LAs get. I still have one in an old plane and it still runs great. Sounds more like you need to twist the needels A little, the LAs are great engines and almost trouble free. Only thing I have had A problem with is the head screws. I have gotten in the habit of pulling them one at A time first thing and adding A drop of locktite before I even fire them.
Old 05-04-2008, 01:14 AM
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Default RE: 46 LA fuel?

Personally I would go through the engine and check for leaks. OS engines like to leak at the o ring under the carb so the first thing I do is coat it in sealer and reinstall it before it sets. Also the rear cover being plastic is prone to cracks and leakage so a good inspection and some sealer there don't hurt neither. I HATE the cheap screws they put in the LAs so I replace the head bolts and muffler bolts with good quality Allen heads available cheap from any good fastener supply store. I am lucky , there is a Fastenall dealer down the street. Have to agree about the Castor content. I personally have switched all my engines to 20% all castor lube. Sig carries it including FAI fuel (no nitro). They also carry 25% all Castor fuels. I find no good argument that anything but all castor is needed in my fuels. I am a sport flyer not in to all out competition and getting that last few rpms from a lower lube fuel is not important to me. I believe if you try the Sig 20% all castor you will find your engine runs "smoother" ( that is the best description I can come up with) . I take extra good care of my engines and the castor getting gummy after setting is not an issue for me.
Old 05-22-2008, 08:36 AM
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Default RE: 46 LA fuel?

I use GX5 for my 46 LA

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