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  1. #1

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    Magnum xls 46 new engine

    Hey guys

    I broke in the engine ,I ran 2-3 tanks of 10% fuel and just followed the manufactures
    directions ok, Then I took the plane flying The manufacturer say now fly the plane and
    very slowly lean a 1/8 turn per flight and you will be done. After 3 flights, I took off for the fourth
    and it bogged down on take off. so I landed fast and richened it up a bit and then it started
    surging That now is my problem, it seems as now matter where I set the high speed neddle
    it surges at full rpm it will surge up a 1000+ rpm and then it will drop a 1000 or so. up and down
    What causes this surge. I have tried 1-3/4 to 4 turns out on the high speed neddle
    and all I get it surging

    thanks David

  2. #2
    aspeed's Avatar
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    Sounds like an air leak somewhere. Sometimes the clunk gets pushed forward after a rough landing and does weird stuff too. Usually just quits at less than 1/2 a tank.

  3. #3

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    Mine had a similar problem. I spent six months troubleshooting mine and finally gave up in disgust after wasting most of a flying season on it. I think they may produce some castings with manufacturing defects, maybe too large an oil weep hole at the front bearing.

    Just return it for a warranty replacement. With luck the second one will be good. My recommendation (some will disagree) is to avoid that engine.
    Last edited by JPMacG; 04-14-2014 at 09:40 PM.
    Glow Head #6, UltraSport #70

  4. #4

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    Air leak.

  5. #5
    proptop's Avatar
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    I would suggest checking all the screws...sometimes if the head or backplate screws aren't quite tight enough, "strange" things can happen...

    Also...the carb pinch / retainer bolt...maybe loosen it, and then push down firmly on the carb while sungging it down again...

    The needle valves on some of these carbs can be problematic too...QC on some of the Magnums can be somewhat "iffy"...
    < Wrongway Feldman's Kreider-Reisner KR-21...(on Gilligan's Island)

  6. #6
    PatrickCurry's Avatar
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    I had an old Thunder Tiger do that and turned out it was the carb barrel sliding back and forth altering the size of the opening in the carb throat. The spring that sat under the screw holding the carb barrel in was worn out and let it slide back and forth. For a short term fix, I bent my throttle wire outward a good bit and installed it back in the throttle arm. That put outward pressure on the barrel, held it in one place and stopped the surging. I didn't have to worry about a long term fix because I was flying in too much wind one day, augured the plane in and smashed the engine to smithereens. You might try to slide your carb barrel back and forth and see if it moves. You wouldn't think so on a NEW engine, but maybe....

  7. #7

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    Thanks Patrick I will check that, as that sounds logical ,

    I also have thought maybe its time to change props as the manufacturer only recommends the prop I have on
    it for break in. I am running a 10 /6 they say 11/7 or 0r 12 /6 or 12/7 will try to run engine this weekend if it gets warmer !!
    I will also check for any loose bolts as others have suggested
    Thanks all
    David

  8. #8
    proptop's Avatar
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    A 10x6 is a good break-in prop...an 11x6 or the APC 12x4 Sport prop are good choices depending on what type of airframe the engine is installed in.

    A 12x6 or 7 is too much prop load on a .46 IMO and might cause other issues...even an 11x7 is getting close to the "too much prop" territory too...depending on the manuf. of the prop. Some props have thick blades, which make the engine work harder, than say, a different manuf. prop w/ same size, but thinner blades.
    Last edited by proptop; 04-18-2014 at 11:08 AM.
    < Wrongway Feldman's Kreider-Reisner KR-21...(on Gilligan's Island)

  9. #9
    jeffie8696's Avatar
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    I run a 10X6 on my Thunder Tiger 46Pro with no issues.
    Obvious question, have you changed the glow plug?
    Club Saito # 677-Team Boca Bearings-Star Collectibles Muscatine-Glowhead Brotherhood #19

  10. #10
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    You might be adjusting the wrong setting. If the engine is "bogging down" on take-off, you might need to lean the low-speed needle a bit, rather than simply adjusting the high speed needle. A half a dozen tanks of fuel may have broken in your Magnum XLS .46 enough that the idle can be leaned out a bit; what was working when the engine was brand new is now a bit too rich.

    I found the Magnum .46 XLS to perform well with a 10x6, 10x7, 11x5, or 11x6 prop. They don't require a lot of nitro, and will run as well on 5% or 10% nitro as they do on 15% nitro. They are fairly high compression motors, so you will likely get better results with a medium-hot plug like the O.S. 8 or Fox R/C Long plug rather than a hotter plug like the O.S. A3 or O.S. 6 (same plug, different model number). If you run an 11x7 APC prop (too much load) with an O.S. A3/6 plug (too hot) and 15% nitro fuel, you'll never get it to run reliably.

    I also found that my Magnum .46 XLS tended to "unload" more in the air than some of my other two-strokes. When adjusting the high speed needle, I found my engine ran better if I turned it back a full 1/3 of a turn rich-of-peak rather than just a few clicks. Your mileage may vary.
    When everybody is out to get you, paranoia is just good thinking!

  11. #11
    Moderator blw's Avatar
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    Bogging down can be a sign of needing a hotter plug, but only after you're sure everything else is just right. No leaks. Right prop. Right fuel. Tuned right.

    BigEd has a good point. I don't use the pinch test. I let the engine idle about 30 seconds and then advance the throttle. If it is tuned well enough to take a normal increase I'll see how fast I can stomp on the gas. I'm looking for how much the crankcase is loading up with too much fuel (too rich low speed needle setting) and how well the plug burns it up. Every engine is different.
    The ultimate responsibility of pilots is to fulfill the dreams of the countless millions who can only stare skyward...and wish.

    "It's a new day for Auburn" - Gus Malzahn

  12. #12
    jeffie8696's Avatar
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    I have had bad plugs cause a surging , it acts like a really cold plug. if it has been used for break in the element gets contaminated.
    Club Saito # 677-Team Boca Bearings-Star Collectibles Muscatine-Glowhead Brotherhood #19

  13. #13
    1QwkSport2.5r's Avatar
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    Ive found on new engines its most often better to have a smaller prop on it until it has some time on it before getting too heavy on the load. Some engines need to loosen up more and thus need to heat up more so rpm is the ticket. Getting the engine to run at its intended RPM while still rich is important. I run my tapered bore engines on 1" less diameter for at least half-3/4 gallon of fuel before loading it down too much. This allows the engine to be run rich while still maintaining rpm (heat). If the engine is on the tighter side, it may take some time before it will throttle well. I have used and do use the pinch test on my Super Tigres with stock Mag ST carbs because the needles seemed to have finer needle threads so it took more than a few clicks or 1/8-1/16 turn to run rich enough on the top end. Otherwise its always good practice to set the high end to peak rpm first and then set the idle mixture for a good transition. I dont go 30 seconds because I've found in my climate that a clean transition at 30 seconds is a tad lean and usually needs to be a tick richer. The real trick is getting the mid-throttle to not get too rich... Some carbs are horrible for not having a linear mid-throttle mixture. Sometimes a good throttle transition and good top end will still end up with a burbly midrange.

    Questionable quality carburetors can make a guy pull their hair out if everything you try doesnt get it to run right... As was said, Magnum carburetors are sometimes suspect so if problems arise that cannot be cured with the normal things, try another carb. Sometimes less nitro is all thats needed to get an engine to purr like a kitten.

    Just my thoughts and observations through my limited experience.
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  14. #14
    Moderator blw's Avatar
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    The long idle test lets you know exactly what is going on in the engine, so you can just bump it up a bit richer if that's how your engine runs. It also gives you a good decision point where you can live with a slight stumble during transition, or try a hotter plug. The for real test is flying the model around and listening to the engine. How does if fly? How is it at half a tank of fuel? The burbly, or wet sounding midrange is too much unburnt fuel. I try to stay away from that condition if I can because you can get into trouble on those long approaches where you may be near idle for 20 seconds, or longer. Having a loaded up engine when you need a go around right this second is asking for trouble. Just my way of going about it. Nothing better than a good carb that tunes well. But it's clear that you know what you are doing so it's just an opinion.
    The ultimate responsibility of pilots is to fulfill the dreams of the countless millions who can only stare skyward...and wish.

    "It's a new day for Auburn" - Gus Malzahn

  15. #15

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    I've owned quite a few of the low cost engines both in cars and airplanes. One thing I have found is that having a consistant feul pressure will help with tuning.Check your muffler any leaks at all causes eratic behavior. These engines are prone to having the mufflers rattle apart.A little bit of high temp silicone at all joints and a tight thru bolt will help, leave the baffles in. Not only do they help keep every thing tight they help to increace pressure to the feul tank.When you feed your carb with consistant pressure you will find that the needle valves will become much more sensitive and a good tune is easier to mantain.All things being equal you'll find that your not touching the needles nearly as much,maybee a click or two as weather changes. The very best way is to get a pump but I realize the extra cost makes the budget engine not so "budget" anymore.

  16. #16
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    The RC combat guys use the XLS .25, with great success. Some guys put a little dab of silicone on every conceivable joint that could leak. The screws that hold the carb on, the O ring area where the carb is mounted, under the nut that holds in the needle valve, everywhere. Likely the muffler pressure fitting would be a good spot, as well as the joint on the muffler.


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