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OS120AX quit & wouldn't restart

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Old 04-11-2012, 05:20 PM
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Stik-n-Rdr
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Default OS120AX quit & wouldn't restart

I ran the OS 120AX on my engine stand going through two about 750cc of PowerMaster 5%. The engine is mounted on a Venus II and was flown on the maiden last week. It was almost dark, and the engine was set way too rich so I did a few circuits of the pattern and landed. I took the plane out on Tuesday morning for the second flight (after leaning the engine a little). After nine minutes, still running slightly rich, I had a deadstick and was able to glide it back to the field ok. Thinking that the tank still had fuel in it, I primed the carb (yes, it squirted out), and tried starting the engine again. The engine sputtered once and never again. I was getting fuel to the carb when priming by covering the carb and rotating the prop, but no fire at all. The glow plug checks out ok. I was only two revolutions from empty when I drained the fuel tank using my Six-shooter pump (yup, got plenty of exercise filling the tank). I fully expect that I'll be fine when I refuel the tank and fire up the engine in my back yard, but am wondering what the deal is here. Is it because I'm only using 5% nitro that I had this issue? I bought a gallon of 15% for a 46AX but would rather stick with the 5% for the 120AX and 160FX I have.

So far my impressions of the engine is that this engine is a tank. It's been fine since day one, and has dealt with the "rich" running very well.

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Old 04-12-2012, 06:01 AM
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Default RE: OS120AX quit & wouldn't restart

Even though a glow plug will glow when you apply a battery to it, it can still be bad. The platinum plating on it can be damaged. It should still fire when the battery pack's applied, though.

If you have good compression, a good plug, and good fuel, the engine WILL fire. If it won't fire, then the engine is either too lean so that there's not enough fuel to fire, or there's too much fuel (flooded) and the excess fuel shields the plug from causing the fuel/air mixture to fire. Not much to actually go wrong.

If you're having difficulties, close the needle valve, remove the glow plug, put a rag over the glow plug hole, and spin the engine over for several seconds (or vigorously flip it) to work out any excess liquid fuel that may be in the engine. Replace the plug; use a new one if you have it. Keep the needle closed, but energize the plug and try to start the engine. After a bit, it should fire and run for a few seconds, burning the remaining fuel that's present. Keep doing this until the engine won't fire. Then open the needle valve to the normal starting position, prime and start. Be careful to not overprime the engine.

Your engine should start easily. Most starting difficulties are due to something in the technique or settings, and not anything actually wrong with the engine. Again, if you have good compression, good fuel, and a good glow plug, the engine WILL fire.
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Old 04-12-2012, 03:35 PM
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Default RE: OS120AX quit & wouldn't restart

I didn't happen to have a spare plug on me or would have changed it out. There was gobs of fuel in the carb, so you're right about that possibly being the issue. I'm used to my 160FX, which fired no matter how flooded it was (or seemed to).

I agree that it's fairly simple, but I was in a time crunch, and haven't messed with glow in a while anyway.

I'll update you when I get a chance to tinker some more. From preliminary indications, this is a strong and reliable engine (other than this issue)....

Thanks,

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Old 04-30-2012, 03:31 PM
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Default RE: OS120AX quit & wouldn't restart

Found the problem. I have to richen the top end mixture about 1/2 to 3/4 turn from optimal (a little richer than usual setting since I'm still breaking in) in order to start this guy. This caught me off guard because none of my other OS glow engines are as sensitive when it comes to "idle mixture" (160FX & 46FX). Flew twice on Saturday with no dead sticks, and had plenty of fun. Since performance is so great, I don't want to start tweaking the idle mixture; I'll probably do it once I've flown two or three more times.

Great engine.....

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Old 05-01-2012, 06:12 AM
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Default RE: OS120AX quit & wouldn't restart

We're very glad to hear that you found your difficulty. As you found out, it's usually something very simple. Every engine is different, and behaves differently from others, even others from the same manufacturer.
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