Fouling glow plugs?
06-06-2003, 01:35 AM
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Fouling glow plugs?
I just recently tried starting my LA-40 engine which failed to start for some reason. So I check to see if the glow plug even worked and the coil would not glow when I had it attached to the glow starter. This was a new glow plug, I can't understand why it would already not work. Could I be fouling my glow plugs somehow? I went to my local hobby shop to find out why this might be happening. The guy said that running at a to high lean mixture would foul the glow plugs. He also said something else that confused me. He said that when you start your engine, that you do not touch the mixture needle, and just fly and break in the engine. But don't you need to adjust the mixture to get optimum power? He said the only time to adjust it is when the humitity is higher or something, I guess I didn't quite understand, but I don't want to fiddle around with the mixture like I have been if that is really the cause of the glow plug not to glow. How come I see guys adjusting their mixtures while their engines are running? I'm confused here. I just want my engine to run with out it quitting in mid air. I know its a mixture issue that I still can't figure out, and now this problem with the glow plugs. If anybody knows how to fix this problem, I would love that. Thanks.
06-06-2003, 02:35 AM
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Fouling glow plugs?
For starters I'd find someone else to talk to...that guy hasn't got a clue. Glow plugs simply can't get fouled like a spark plug does. You say it's a new glow plug but does that mean straight from the pack or the engine's had a couple of runs on it? It's not unknown for a new plug not to work but it's rare. If the engine has been run a couple of times (or even once) then it's possible for a piece of aluminium swarf to get lodged on the plug coil. This is the worst think for a plug and it'll burn out instantly where the aluminium touches it. But first, is your glow starter battery charged up? Do you have another plug to try?
As for this business about not touching the needle valve...the manual might say 1 1/2 turns out or whatever but this is a guide only and if you don't wind it in then back out you're relying on the guy in the factory doing it properly. For a first start I always wind the needle out at least one extra turn. For one thing, an engine will always start if it's too rich but not if it's too lean. You must avoid running it lean, especially when it's new, so some needle valve twiddling is necessary. Don't start and fly...it should be run in for a while either on the bench or mounted in the model.
Another thing too. The LA doesn't use ball races for the crankshaft, it's what's called a bushed engine and the correct fuel for them has at least 20% oil and most of that should be castor. Use the right fuel and a bushed crankshaft will virtually never wear out.
As for this business about not touching the needle valve...the manual might say 1 1/2 turns out or whatever but this is a guide only and if you don't wind it in then back out you're relying on the guy in the factory doing it properly. For a first start I always wind the needle out at least one extra turn. For one thing, an engine will always start if it's too rich but not if it's too lean. You must avoid running it lean, especially when it's new, so some needle valve twiddling is necessary. Don't start and fly...it should be run in for a while either on the bench or mounted in the model.
Another thing too. The LA doesn't use ball races for the crankshaft, it's what's called a bushed engine and the correct fuel for them has at least 20% oil and most of that should be castor. Use the right fuel and a bushed crankshaft will virtually never wear out.
06-06-2003, 02:39 AM
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Fouling glow plugs?
Was your glow starter charged up? I see no reason for the plug to just not work. Yes, you do mess with the needle valve when the engine is running. This is how you get your engine to perform good. But, when breaking in your motor, be sure that you run the engine slightly rich. You want a little more lubrication in the engine when breaking it in so you dont burn up the piston and sleeve. Take your needle out 2-3 full turns out to break in the engine. You can tell if it is rich by the ammount of smoke comming out of the muffler. Hope this helps. Justin.
06-06-2003, 04:11 AM
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Fouling glow plugs?
I once bought a card of 12 glow plugs. Six were dead on arrival. Never assume anything.
Glow engines need to be reneedled every time you begin a flying session. Those that do not check their engines for tuning during the first flight of the day are inexperienced and are taking a chance of ruining their engines. OR, there are special circumstances that you, a novice, will not encounter for a good while to come.
As Downunder stated, open the needle valve (high speed mixture) one or more turns further out than the starting point specified in the manual. Too much fuel will not harm your engine, as long as there is not enough fuel in the cylinder to prevent the engine from turning over. Too little fuel (too lean) can damage your engine permanently in just a few seconds of running time. Always go for rich - never for lean.
Find someone else to take advice from other than your hobbyshop/dealer. If he/she truly told you what you said he told you, he/she doesn't know what he/she is talking about.
Hang in there. There is a lot to learn, but you can do it.
Glow engines need to be reneedled every time you begin a flying session. Those that do not check their engines for tuning during the first flight of the day are inexperienced and are taking a chance of ruining their engines. OR, there are special circumstances that you, a novice, will not encounter for a good while to come.
As Downunder stated, open the needle valve (high speed mixture) one or more turns further out than the starting point specified in the manual. Too much fuel will not harm your engine, as long as there is not enough fuel in the cylinder to prevent the engine from turning over. Too little fuel (too lean) can damage your engine permanently in just a few seconds of running time. Always go for rich - never for lean.
Find someone else to take advice from other than your hobbyshop/dealer. If he/she truly told you what you said he told you, he/she doesn't know what he/she is talking about.
Hang in there. There is a lot to learn, but you can do it.
06-06-2003, 06:50 PM
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Fouling glow plugs?
Well, its not a new engine, its about 3 years old so its been run in pretty good as I have been flying for 3 years. But only now did I really start to notice the problems. The glow starter was fully charged and I tried it on a new glow plug and it would glow where as with my other glow plug, it wouldent glow. I also have a temperature gage on my field box where the glow starter can be plugged into, and the needle was not moving with the dead plug, but sprung to life with the new one. I noticed in the dead plug that there was some fuel in the coil. Could this ruin the plug? I had at least 2 flights on that glow plug before it gave out. Before I even replaced that one, I had one in there that was about 2 years old that gave out. But I know cheifly my problems are in the adjusting the mixture part. I know how to fly airplanes, but I still don't quite understand how to handle the engine and adjusting the mixture and everything. The guy woulden't really answer my question, so I didn't bother futher. What I was trying to ask him was what mixture setting does the needle have to be at when starting the engine? Full rich? Full lean?(that I now know not to do) Half? But I guess it does say in the manual, so I will take a look in it. What about the airbleed adjustment? What should that be at? That is one thing I haven't really touched because I don't really know what it does.
06-07-2003, 03:55 AM
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Fouling glow plugs?
Having fuel or even oil in the plug won't do it any harm. What you see in there is just some fuel left over from trying to start the engine with the plug burned out. Just a tip, disconnect the glow starter before you run the engine at full throttle or the added heat can burn out the plug. It seems like in this case you just got a bad plug.
As for the mixture when starting...if it's been properly tuned the last time it was run (slightly rich) then leave the needle setting alone. I almost never have to alter the mixture but I'll check it by pointing the nose up just in case. The airbleed adjustment is only for the idle mixture. If you look through the hole in front of the carb you should see the end of the little screw partly blocking it. What the screw does is vary the size of the hole that lets a small amount of air leak through into the carb at idle. Because you only have one needle valve to regulate fuel flow (and that has to be set for what's needed at full throttle) then the mixture at idle can only be changed by how much air you allow to leak through the hole. So by winding the screw out the hole gets bigger which means more air leaks in to make the mixture at idle leaner. Winding the screw in makes the hole smaller and the mixture gets richer.
This is the best way to find out if it's rich or lean at idle. Pinch the fuel line with your fingers to stop any fuel going into the carb and listen to the revs. If the revs get higher quite noticeably for a few seconds before starting to die then it's too rich, you need to bleed more air through that hole. Turn the screw out a little and try again. What you want when you pinch the line is to hear a small rise in revs very briefly before it starts to die. If you pinch the line and the revs start to die straight away with no increase then it's too lean. Wind the screw in a little and try again. When you get the mixture set correctly you might find that your idle revs have increased a fair bit so just readjust the idle speed setting.
As for the mixture when starting...if it's been properly tuned the last time it was run (slightly rich) then leave the needle setting alone. I almost never have to alter the mixture but I'll check it by pointing the nose up just in case. The airbleed adjustment is only for the idle mixture. If you look through the hole in front of the carb you should see the end of the little screw partly blocking it. What the screw does is vary the size of the hole that lets a small amount of air leak through into the carb at idle. Because you only have one needle valve to regulate fuel flow (and that has to be set for what's needed at full throttle) then the mixture at idle can only be changed by how much air you allow to leak through the hole. So by winding the screw out the hole gets bigger which means more air leaks in to make the mixture at idle leaner. Winding the screw in makes the hole smaller and the mixture gets richer.
This is the best way to find out if it's rich or lean at idle. Pinch the fuel line with your fingers to stop any fuel going into the carb and listen to the revs. If the revs get higher quite noticeably for a few seconds before starting to die then it's too rich, you need to bleed more air through that hole. Turn the screw out a little and try again. What you want when you pinch the line is to hear a small rise in revs very briefly before it starts to die. If you pinch the line and the revs start to die straight away with no increase then it's too lean. Wind the screw in a little and try again. When you get the mixture set correctly you might find that your idle revs have increased a fair bit so just readjust the idle speed setting.
