Just a thought that occured to a few fellow flyers over the weekend , wouldnt it be smart to make a larger glow plug for larger engines? The discussion took place while running a ST 2300 inverted on a new plane. After 5 tanks and 2 plugs later we came to the conclusion if they made larger glow plugs to be able to handle the larger volume of oil and gas the larger engines consume the glow plug would last longer , burn better and make the engine run better. Why is it a glow plug is designed to fit a 40 size engine all teh way to a 120 size engine? It's the same size and the same fillement but it has to handle up to three times more fuel and expect to be able to keep lit. I am aware you can by a hotter plug but its still the same size just different thickness and composition of the fillement inside. What if a engine manufacturer made the engines with larger holes and larger glow plugs so we could run them inverted and not have to worry about a flame out or burned plug? You dont use the same size spark plug in your weedwacker as you do in your car so what is the theory behind the same size glow plug for most glow engines? We could cut down on glow plug failure ,reduce engine tuneing problems and maybe even burn the fuel more efficiently with a larger plug. Any theorys as to why a engine has not been made this way yet?

There are engines out there with 2 glow plugs in the head.

However, I'm not at all sure a bigger plug would make running inverted easier. It might, but it might also make it worse. A bigger plug would mean a bigger area for fuel and oil to pool.

And a bigger coil isn't necessarily a great thing. Glow plugs work by creating a catalytic reaction between the platnum in the plug and the methonal in the fuel.

If you can afford some custom machine work, you could probibly get a duel plug head made for your engine and see what it does. At least with two normal size plugs, you create two ignition sources, which, in theory, leads to a more even and complete fuel burning, at least that's how it was explained to me. I've no idea if it really works well or not.

Oh, and fwiw, not all plugs are created equal. You can get heavy duty plugs that do have much stronger elements for high compression engines and such.

And if not careful you can get a longer plug that increases the compression which is a no no. (i think )

Thanks for the info guys. The super tigre 2300 calls for a OS #8...kinda standard plug i thought. I inverted it and it seemed to like to foul this plug out so I switched to a "hotter" plug and it runs ok but doesnt like to idle for a very long time.

You could be just trying to idle too slowly. Inverted engines don't idle as well as upright or side mounted ones, no matter what kind of plug you have in them. It's also common to see onboard glow ignition hooked to the throttle channel on inverted engines for just the reasons you are discovering. There's a really cool (a bit pricy though) gadet out there that provides current to the plug based on the plug's condition rather than the throttle setting, I've heard some really good things about it, but I keep forgetting what it's called or who makes it. (useless info, I know).

5_spot, actually, I personally use K&B plugs because they are a bit longer (and a lot less expensive) than the OS plugs. I get a few extra RPM out of the engine that way with no problems. Sometimes a little extra compression is a good thing .

I will list three things that will enhance your idiling problems.

1. Use an OS 4 cycle glow plug

2. Switch to YS 20/20 glow fuel

3. Instal an onboard ignition system


This is a sure fix to any problems relating to an inverted 2 cycle glow engine installation.

Well I have a reliable idle at 2000 rpms now. It will idle for up to 3 minutes now and still transitions good enough to fly. Thanks for the info guys.

Btw, you didn't say if hte engine was new or well broken in prior to being mounted inverted. As you may know, a good, low, stable idle takes a while to develop, espeically on the larger ringed engines. So that might be part of your problem as well.

flycatch, makes a couple of good points that can be generalised to any 4-cycle plugs, or the Fox Miracle plug will help, they are hotter than most 2 stroke plugs. You already said you went to a hotter plug, maybe going hotter still will help.

More nitro helps most engines idle better and makes them less sensitive to mixture settings. Since half the problem with an inverted engine is getting the idle mixture sorted out, more nitro from any brand fuel is going to be a good thing.

2k for an inverted engine sounds pretty darn good to me.