EGT's & Main Jets

CLS447

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I got to fly my single place with 503 for the first time since last year ! It felt really great. She flies beautifully but there are a couple of things that bother me.

The first is....when she sits for more than one week, don't even try to start her until you drop the carb bowls & empty out the oil saturated gas in them. Then she will start just fine.

The 2 banjo fittings, with the check balls in them ,on the oil pump, are still leaking though.
Anyone else ever have this problem ????

The other thing is ....both EGTs read a solid 900 degress & the CHTs get to 350. Does this sound like I need smaller main jets ? The factory installed main jets are .158 .

Sounds like they are too rich.....What do you think ? Thanks
 

DennisFetters

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Yes, too rich.

If you run your EGT's too low, and your engine inverted it will become hard to start.

For a longer life on the engine, you need to run the EGT's around 1150F at full throttle, but change your needle jet and position so that at cruse you are around 1050 t0 1100F. Below 1000F is not burning the oil and you will clog the rings and build up carbon on the heads.

The banjo fittings are a one-way valve and must be changed if they leek, and that too will make your engine hard to start.

Hope that helps.
 

dabkb2

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Are those the same temps for a 582?
 

Jpipe

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Starting my Single Carb 503, I turn on the gas valve. I have short plastic tube that connects to the overflow tubes with a tee. To that tee, I have another removable tube that I first suck a little, to make sure the fuel bowls are full and the blow until a drop of fuel drips out of the air filter. Then pull start, it starts every time.

The temps , I can't help you with.
John
 

DennisFetters

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Are those the same temps for a 582?
Yes, for basically any two-stroke engine measuring the ETS's from the same distance from the piston face. The reason why is that there is an ideal mix ratio for fuel and air, and that will burn at a specific temperature. Anything below that is combusting a quantity of fuel in the exhaust system and waisted, besides carboning your piston and rings.

Adding to this I should say that this all assumes you have the engine setup correctly and running the engine at 6500 rpm at full throttle. As said in a later post, your prop pitch must be set correctly.

It is worth to say that yes, it would be hard to start your engine if the carburetor bowls are not full. I always used a squeeze bulb. But a primer will also make it start better.
 
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Stevep55376

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You may want to check your prop pitch, my 447 was running low EGTs and after attending an EAA seminar by Brian Carpenter realized I had too much pitch, after taking pitch out of prop and getting my RPM up the EGTs went up and my CHTs came down. Google search "EAA Brian Carpenter" and select video on " is your 2 stroke about to fail"


EAA Video Player - Your Source for Aviation Videos
www.eaavideo.org/video.aspx?v=626943072001
Is Your 2 stroke Engine About to Fail? Presented by: Brian Carpenter of Rainbow Aviation Services. Hosted by: Steve Buss.

Let us know if this works for you also.

Good luck, Steve
 

CLS447

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My full power RPM is 6500. My 503 starts & runs fine. There is some oil leakthrough when it sits for a while. I will be replacing those banjo fittings.

So.....like I said, with the factory installed .158 main jets I am only seeing 900 degrees on both of my EGTs.

What size main jets are all you guys using in you 503s ?

If I am going to order some main jets, what size do you think I should get ?

If I only drop one size, I may see very little change & I will have to get more.

Here are some jets......I don't like the price, I need 2 of each. !!

http://store.leadingedgeairfoils.com/index.php?cPath=551_557_488

Does anyone know the size graduations ?

Does anyone have any smaller ones ( in pairs ) that they would like to sell or loan ?

BTW ...Dennis, in just about all "agressive " flying.... I am at least at 5000 rpms. Is that "on the main" jet ?
 
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CLS447

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I sure would like to verify my guage readings but..... 2 guages & 2 sensors both reading identically, I tend to believe them......is that foolish ?
 

rickloon

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What is your DA? That will make a lot of difference in the jet you need,also rotax has a chart for jet changes for differant temps and alt.
Rick
 

DennisFetters

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My full power RPM is 6500. My 503 starts & runs fine. There is some oil leakthrough when it sits for a while. I will be replacing those banjo fittings.

So.....like I said, with the factory installed .158 main jets I am only seeing 900 degrees on both of my EGTs.

What size main jets are all you guys using in you 503s ?

If I am going to order some main jets, what size do you think I should get ?

If I only drop one size, I may see very little change & I will have to get more.

Here are some jets......I don't like the price, I need 2 of each. !!

http://store.leadingedgeairfoils.com/index.php?cPath=551_557_488

Does anyone know the size graduations ?

Does anyone have any smaller ones ( in pairs ) that they would like to sell or loan ?

BTW ...Dennis, in just about all "agressive " flying.... I am at least at 5000 rpms. Is that "on the main" jet ?
Chris, jetting your two-stroke aviation engine is absolutely the most important engine care you can do, and absolutely necessary to achieve the longest life of the engine and for it to be at peek reliability. This is one of those things you want to spend money on.

Anyone that flies a two-stroke should have a complete set of main jets that will cover summer and winter operations. It don’t cost that much, but it’s critical that you dial your engine in. I always flew around with my jet pack and a wrench, just in case. My range was everything between 148 and 165 for my 503.

I can’t guess if just one size will get you where you need to be or not. It’s just one of those investments that I know I need and I don’t question the cost.
 
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multimike

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Before you trust your EGT gauges, check the color of your spark plugs. The plugs tell all about your mixtures. The color should be a light chocolate brown/ dark tan after running at your cruise rpm for at least 10minutes then shutting the engine off without idling long. Let the engine cool before pulling the plugs- do NOT remove plugs on a hot engine! Once the plug are at the right color, what ever the EGT gauges are reading is the right temp.
Good luck
Mike
 

bryancobb

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Agree With Dennis AND Mike!

Agree With Dennis AND Mike!

..The color should be a light chocolate brown/ dark tan ...
The only thing that may be confusing is the term "chocolate brown."

The color of the plugs if your mixture is right will be really tan/beige. If there's any black on or near the electrode/insulator...IT IS TOO RICH. If there's any white specs then you are too lean.

If you set your prop pitch according to the prop manufacturer's instructions FOR YOUR ENGINE, that should get you "close enough to correct," to be able to jet your engine. Then you will need to set your prop pitch again.

The 6500 RPM at full throttle means static RPM on the ground. It the air, it will increase a little.

IF your EGT's don't reach 1150 during an extended time (2 or 3 minutes) at full throttle, install the next smaller main jets and keep repeating this until they do.

Then and only then, you can adjust the midrange. The midrange is wrong unless...as you SLOWLY decrease throttle after the 2-3 minutes of wide open, there should be a similar, gradual decrease in EGT's. If EGT's start to rise while you are decreasing throttle, they are too lean and need richer needle jets.

The long skinny needles are the JET NEEDLES. Don't change them. The ones you change to adjust the midrange are the NEEDLE JETS. They look like an RC Airplane Fuel Tank Klunk if you know what that is.

If you fly a 2-stroke engine, you MUST spend $200-$500 on jets to be safe unless you live somewhere the weather is constant all year round and/or you don't vary your altitude very much.
 

Georgi

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..not highjacking but

..not highjacking but

I cold start my Rotax 503 SC with one or two pulls. But after stopping the engine starting again takes a real effort. Do you have any idea why and how to fix it?
Thank you.Georgi.
 

big mike

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Multimike was right never trust egt guages, I have hundreds of hour on a dyno running two strokes. I can tell you a couple of things you can take to the bank. First where you put the probe makes allot of difference in the reading. The reason being, the charge continues to burn for a second after it leaves the cylinder. So the exhaust mass reaches peak temp at about 10.5" inces from the piston skirt. A probe that reads 950 deg. at 6" will read 1200 deg. at 10.5" on most engines. Exactly reverse of what most people think.
Second, if you start moving your jets leaner you will reach a point where you loose the controlled burn, and the charge starts to explode from heat generated by the piston and head before the spark plug ignites the charge. We call this pre-detonation, because _all of the charge burns in the cylinder your trusty egt will suddenly drop from 1250 to about 1050. Most folks think they need to lean it more. (They usually tow the craft back to the airport.) Learn to read plugs, look at the pistons. When you get those right what ever the egt says that's where you should run the engine.
 

big mike

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I have been doing R&D on 2 strokes for about 40 years now and have hundreds of hours dyno testing. I'd like to throw in my 2 cents worth. No one should ever trust an egt without serious testing first. They lie, and here is how, try installing the richest jets you have, the engine will not even clean out. but your egts will read 1500 degrees because your unburned charge is burning in the manifold causing your egt to go ballistic. next, jet the engine too lean and the egt will read 950 because all of the charge is burning in the cylinder. And will very soon start to pre-detonate and turn your piston to putty. An egt guage works over a narrow range of jets.
When you check your plugs, to verify your egt. Look carefully at the ground electrode. There will be a color change on the electrode, it will be lighter toward the tip and darker toward the treads. if that color change happens very close to the tip you are a little rich. If it happens at the base where the threads are, you are too lean. perfect jetting will result in a color change on the bend about mid point. Liquid cooled engines will have a darker color around the base, and it may even be black. It is only because the heat is transferred faster because the head temp is cooler. Pay little attention to this. If you have a nice brown paper bag color around the base you are probably running a fan cooled engine. Hope this helps.
 

CLS447

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Thanks guys ! That webinar radio show was also very interesting, too !

Big Mike.....When I had a 447 premix on the same gyro I had one EGT gauge & probe & I installed the probe the way the instructions told me to. I drilled a hole where the 2 pipes come together (in the exhaust pipe after the wye pipe ) it was a clamp on probe.

I was seeing temperatures of 1400. The other guys got me real concerned about these high temps, so they had me change the clip setting on my needle with no change. So I got some bigger main jets......still no change , so we just started drilling the the jet out till I finally got those temps down ( much larger than factory size), then I purchased that size jet & flew happier for a year or two. ( single carb 447 )

Then Rotax started selling the wye pipe with the threaded bungs that were at the proper position for threaded thermocouples. So I got one & moved my EGT probe & added another.

The temps were way low !! Went back to the factory sized jet & it was perfect ! That taught me a great lesson about probe placement & Rotax's factory jet selection.

Now I have the 503 oil injected dual carb & I am seeing these low numbers. I feel Rotax probably has the right jets again & I am reluctant to change them.

I have never had to change my jets to accomodate changes in temp & altitude( pretty consistant when & where I fly).

So this is what I plan to do........I will start reading my plugs as suggested, & maybe get a set of jets 2 sizes smaller than what I have. I will watch those temps closely & read those plugs.

Fuel savings & better temps are my goal. How much less fuel will it burn, I wonder ??


One more thing......My exhaust pipe is the same pipe I used on the 447 because it had been JET-HOT coated.
The pipes are the same for both engines, but the wye pipe is different. So for the first year or two with the 503, I ran that uncoated wye pipe. Well it started rusting & looked ugly compared to the rest of my exhaust, so that winter I pulled off the wye pipe & sent it out to be coated as well.

When I had the pipe off I inspected the rings & cumbustion chamber. The rings & chamber looked just fine but there was alot of carbon clinging on the inside edges of the exhaust gaskets. I don't like the way the gaskets are actually smaller than the port itself.

I hate to have to pull my wye pipe again to do an inspection, that may wait till the end of the season, but maybe not.

What should the exhaust port & pipe look like ? (color & such )

Also, is it possible that it is over-oiling due the banjo/check leak that I am having ?

BTW......AV-2 oil & Iridium spark plugs. Non ethanol 89 octane fuel with Yamaha Ring -Free (1 ounce per 10 gal)
 
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CLS447

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Yes, too rich.

For a longer life on the engine, you need to run the EGT's around 1150F at full throttle, but change your needle jet and position so that at cruse you are around 1050 t0 1100F. Below 1000F is not burning the oil and you will clog the rings and build up carbon on the heads.
.
Dennis, I know that you are familiar with my specific gyro, right ?
I am about 195 lbs & have 12 gallon of fuel on board.

What do you think my cruise RPM would be ?
 

DennisFetters

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Dennis, I know that you are familiar with my specific gyro, right ?
I am about 195 lbs & have 12 gallon of fuel on board.

What do you think my cruise RPM would be ?
It has been a long time since my butt would fit into a Commander 503, until only these last few years, and then I haven't had the opportunity to fly a 503 Commander.

I'm guessing it was around 4800rpm, but I can't be for sure now, but the most fuel I ever had on board was 5 gallons. Too many years ago. Sorry I can't be of more help with that.
 
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