Gas engine tuning for newbies....

[bob_nj]

mfuess --> I gotta tell you that I went to the field today and tried your tuning method.I took my time, used a tach, and got great results!I've been running gas engines for about 5 years now, and am not a know it all by any means. What you said though finally sunk into my brain.It works, it truly works. I'm convinced that alot of the threads I read about engine problems can be solved if more people really understood how these carbs work.Hats off!That being said, let's talk about something..You say in one of your posts that a 2 cycle engine should never four stroke while it's running, ever.Don't remember where I saw that, and forgive me if I've mis-quoted, but let's use that as a premise.My engine now runs like that, really smooth, one click on the throttle notices an engine response, and runs great in all attitudes. Inverted and knife edge are flawless.Truth be told, it makes me really really nervous to have my engine run so good.It has to be my glo engine mentality that's been burned in over the years.To add another's opinion, here is a quote from the site of Blain Austin here -->http://www.blaineaustin.com/engines.htmIf my engine keeps quitting what should I do? I get asked this all the time. The first thing you should do is richen the high end needle value. What causes the engine to quit is that its getting hot. If it is running rich it will not quit. Avoid it running smooth. You want it to have a little burble. If it sounds like a sewing machine, well that's not good. That means it is going lean and it is getting ready to quit. Don't be afraid to turn the needles. I have guys all the time tell me there engine isn't running to peak performance but they are afraid to turn the needles. Always remember rich is good and safe but don't sacrifice performance because your afraid it will get hot.Here's the gyst of my question to you.The part where he says -> "Avoid it running smooth. You want it to have a little burble. If it sounds like a sewing machine, well that's not good." is what makes me a little nervous.My engine is running great, and it's because it is running smooth.When I got a one click throttle response, I knew it was smooth.Myself and a ton of others are always concerned about a flameout for whatever reason.Blaine mentions going lean, and it sounds like he means on the top end. My reason for concern is that I like to harrier, hover, and otherwise fly low and slow with the nose in the air. I am always thinking about the motor leaning on the low end in these attitudes, or just quitting?So to summarize, is it possible to tune your way and have the possibility of it being a hazard with the type of flying I like to do?Thanks again for your timeBob

[mfuess]

Bob nj,

I'm glad you are tuning properly. Way too many pilots tend to tune their gasser like a glow engine, and that just doesn't work too good. There is a fine line between "running perfect and running lean". But you will also find that it's very much worth the trouble to have your engine running sewing machine perfect especially when performing low altitude, instant throttle demand maneuvers.

Let's stop and consider what's REALLY going on when a two stroke engine IS "four stroking";

In order for a two stroke engine to four stroke, it has to mis-fire every other cycle. When your two stroke mis-fires, the sparkplug is so wet it momentarily shorts out the electrode & anode. THAT'S NOT GOOD. Also, when it mis-fires the engine is operating on power generated from the PREVIOUS cycle, instead of generating a new power stroke. THAT"S NOT GOOD EITHER.

So, when a two stroke is four stroking your fouling out your sparkplug, running on half the power it should deliver, wasting gasoline, and substancially lowering the operating temperature.

The perfectly tuned two stroke engine delivers consistant power every single stroke, its clean burning, very efficient gas consumption, no sparkplug fouling, and operates at its best operating temperature. It will also deliver smooth throttle responce throughout the entire throttle range. THERE IS A DOWNSIDE. A Properly tuned engine is tuned at operating temperature. So when the engine is cold, it is not in tune. In fact, your engine is a little a bit LEAN. Therefore you MUST let the engine get up to operating temperature BEFORE you fly, or it will die on throttle demand. This is the part most pilots don't like! Personally, I much prefer letting my engine warm up then let it run like a fine tuned Rolex. I get constant comments on how great my engine runs. To which I say, all I do is tune it properly and let it warm up BEFORE I FLY. I have NEVER had an engine die in flight, EVER.

[bob_nj]

Sorry about the one long paragraph in my post.I'm working with Max on it now and am trying to get is sorted out.So you are saying that if the engine sounds like a sewing machine, and is not four stroking, even in a harrier or hover, not to worry?Take CareBob

[mfuess]

Not to WORRY.
But do listen to it, and fine tune if needed...

[Tired Old Man]

No worries mate. When it's running right it doesn't burbal or 4 stroke. Mine never quit in flight unless they run out of gas.

[mfuess]

	Quote: Originally Posted by silversurfer
	No worries mate. When it's running right it doesn't burbal or 4 stroke. Mine never quit in flight unless they run out of gas.

And that's the way its supposed to be!

[rcflyer]

mfuess and others, I would like some comments on this tuning method from pp23-24 "Gas Engines-Giant Planes" by Don and Judy Apotolisco 2nd Ed:

High speed adjustments

The following procedures can be used with excellent results:
-Start the engine and allow it to warm up
-Accelerate the engine to full throttle
-Read the tachometer
-Pinch the fuel line to the carb
-Watch the initial rpm change
If the engine is adjusted correctly it will rise about 200 rpm and then quit from fuel starvation. If the operator is fast enough to observe the initial rpm change on the tach and release the line, the engine will continue to operate without quitting. If the engine rises more than 200 rpm it is too rich and the high speed needle needs to be leaned until the rpm rise is about 200. If the rpm rises less than 200 the engine is set too lean and needs to be richened.

Idle adjustments

With the engine at idle rpm, pinch the fuel line. You should see a slight increase in rpm and then the engine will quit. If the rpm increases more than 200 rpm the engine idle is too rich and needs to be leaned out. If the rpm drops immediately or quits the idle mixture is too lean and needs to be richened. Once the idle mixture is set the high speed settings need to be rechecked and if necessary adjusted per the above method.

Thanks!

[bob_nj]

I know you said that quote is from a gas engine book, but that sounds like the method we've used for years on glo engines?

Don't know about anyone else, but there is no way in hades I can, or would want to try to get close to the fuel line on a giant engine. Just my opinion.
Bob

[rcflyer]

Bob, yeah I used the pinch method on all my 2C and 4C glows too, but this book was recommending it for gassers. Don (of Don's Hobby Shop) is an experienced person and there should be some merit to it. Just asking for views.

[bob_nj]

Understood!
I guess my view is that it will be very difficult to get to (cowling), nevermind reach my giant engine's fuel line.
Second point is that I didn't know that method worked for the types of carbs and fuel delivery systems on a gasser?

Let's see what others say...

[mfuess]

	Quote: Originally Posted by bob_nj
	Understood! I guess my view is that it will be very difficult to get to (cowling), nevermind reach my giant engine's fuel line. Second point is that I didn't know that method worked for the types of carbs and fuel delivery systems on a gasser? Let's see what others say...

NO. Gassers are not GLOW engines and you don't tune them as though they are.

[bob_nj]

mfeuss --> Does that mean you agree that the method is for glo mentioned in the book?

[rcign]

Generally works the same, except a gasser carb has fuel in a chamber under the diaphragm, and it takes a while to burn off enough fuel to tell it it's rich or not...
Try it some time, take the fuel line off the carb and see how long it takes to die...

[jfassino]

	Quote: Originally Posted by mfuess
	NO. Gassers are not GLOW engines and you don't tune them as though they are.

mfuess,

Great thread, could you share why tis does not work..It is always easier for me if I can understand why? Is the carb the issue?

Thanks for all of your comments and help.

Jim

[mfuess]

Glow engines use exhaust pressure to supply fuel to the carb. As the fuel level changes, so does the available pressure to the carb. So the tune changes as the fuel level drops. Because of this, you have to run a glow engine slightly on the rich side. Gas engines on the other hand, use a fuel pump to supply gas to the carb. Fuel pumps maintain constant pressure regardless of fuel level so the carb doesn't see any fuel level change, thereby the tune doesn't change.

To give you an idea of how effective a pump is, I bench ran a 45cc gas engine with the gas tank resting on the floor. It was a 4 foot drop below the engine and about 5 feet of fuel line. The engine ran perfectly as it always did. Try that with a glow engine and it won't even start.