503 exhaust gas temps

[cgmg]

I've been trying to dial in my carbs to get my 503 exhaust gas temps into spec, which is 43 degrees or less difference between cylinders. The best I've been able to do is get the temps about 20 degrees apart up until 6000 rpm or higher. At wide open throttle, the difference climbs to 80 degrees plus, with the #1 cylinder running hotter. The only way I've been able to overcome this is to set the carbs so cylinder #2 runs hotter up to the 6000 rpm point, but being over the recommended temperature difference. This doesn't seem like the right thing to do, so I'm leaving the carbs set for temps to be close up to the 6000 rpm point.

Anyone out there have any suggestions as to what is going on, or is this typical of 503's. I've checked my clips, needle jets, and jet needles. Everything matches up. The only changes I made over the winter were rebuilding #2 carb, which is older than the #1 carb. I also changed my main jets to 155 from 158.

Any help, or things to look for, would be greatly appreciated.

Mark

[gyropilot]

Mark,

I have a similar problem with my dual carb 503... the EGT spread always varies between about 40 to 80 degrees F. I've just learned to ignore it because I've been unable to find any cause for it... other than maybe crappy probes or the dual gauge itself.

I've torn my engine apart twice in the last 150 hours for cleaning, new seals, gaskets, etc., and I've never seen any sign of problems from the apparent excessive EGT spread. I've also carefully rebuilt the carbs twice.

I've just attributed the EGT readings to possible minute differences in the probe manufacture, their locations within the exhaust manifold, or the construction of the exhaust manifold itself. One of the runners on the exhaust manifold is not quite as tall inside as the other... manufacturing tolerance at Rotax I guess.

The CHT is also always cooler in the front cylinder as well... undoubtedly from receiving the bulk of the cool air from the fan.

Relax,

John L.

[Aussie_Paul]

You have both probably done this, but it is a good idea to swap the probes in the manifold for a test.

Once you know where the problem is you just have to allow for the difference.

Non aviation un calibrated gauges have convinced people to adjust things and do serious damage to the engine and also to the gyro if the engine stops at the wrong time!!!!!

Aussie Paul.

[mceagle]

It is very hard to have both cylinders on a 503 to have exactly the same compression. Unlike the 582, the 503's do not have proper crankcase pressure seals between the cylinders, so uneven crankcase compression means uneven mixtures and consequently different temperatures.
Two strokes are always set to run a little on the rich side to be on the safe side. Variations in the EGT are not critical as long as they do not do over a certain figure. What that figure is depends on guage accuracy, correct wiring and the probe placement.

[gyropilot]

Mceagle and Paul:

Well put!

The stock recommended jetting from Rotax seems to be a little on the rich side on my 503 (EGT's are usually on the low side of the green range) and I've just avoided trying to "optimize" things by jetting leaner. The slightly richer mixture (than optimal) is my insurance policy against the Chinese manufactured dual EGT and CHT gauges I use... not that Westburg gauges are much better.

John L.

[Doug Riley]

I think this is one of those KISS cases. Check the plugs' color -- if both are chocolate brown, the exhaust temp is correct, no matter what that little plastic guage says.

[automan1223]

Buy a bunch of sets of jets richer in each step. Run them up number at a time until the motor "4 strokes" you will know the sound when you hear it at full throttle then back them off a number or 2 until it does not 4 stroke. The engine will run fat but safe. Anything the egt says after that is engine blueprinting issues, ignition timing, gauge issues, etc. Tuning by ear and plugs is the best route. Egt gauge is just to confirm it. The engine may make a little bit less power rich/fat mix but you will save the engine in the long run. Talk to the guys at lockwood if you want any other technical questions. Also switch carbs to see if its a mfg tolerance between new and old flow rates. No 2 are ever the same !

Jonathan

[cgmg]

Everybody,

Thanks for the suggestions. Actually, last year I had to lean my carbs out, as I kept having trouble with carbon buildup on my plugs every 10 hours or so. It also got to where the engine would bog down in midrange rpm's on takeoff. According to my probes, though, the temps were not more than 60 degrees out.

I do check the condition of the plugs, and since re-jetting for a little leaner, my plugs look about the right color, and I'm getting 25 hours out of them without oil or carbon deposits on them.

I took the exhaust off this winter to paint it, and my inspection of the rings, pistons, and cylinder walls showed good conditions in all 3.

Paul's idea of switching probes is good, but my engine is the older style, and I have to bend the end of one probe to get it into the exhaust manifold. Based on what I'm hearing here, I don't believe, at least at this point, that my problem(if it really is one), justifies buying a new probe, and tearing my harness apart to get to it.

I'll pass on my experience if anything comes of this situation as I fly this year, though.

Mark

[Aussie_Paul]

Mark, just swap the wires at the instrument. Aussie Paul.

[cgmg]

Paul,

I can probably try that. My connections for the temp probes are in a short piece of wire harness cover that I could pretty easily open up and switch the leads.

Thanks,

Mark

[CLS447]

Mark, I am waiting to see what happens when you switch leads. I had the same problem years ago, I switched leads & it was the instument or sender. Now I just read accordingly.

Look at the right CHT. It runs 100 degrees hotter than the left. uh oh, now you got me thinking,was it the gauge or the sender or was the rear cylinder hotter? Damn , now I gotta recheck!

I think the gauge just reads 100 hotter. Damn memory! Now I can't even remember which is for my front & which is for my rear cylinders. This year I am gonna mark them! I think the Left CHT/EGT is for the rear.

[mceagle]

What, no drift flag.

[CLS447]

Nope but I've been thinking about that piece of yarn. I always head straight for my target anyway! Could someone explain it to me again please .

[mceagle]

"I always head straight for my target anyway!"

Chris,
That is exactly the reason that you need a drift flag - a very important instrument, especially in a low speed aircraft.

[StanFoster]

Chris: The yaw string keeps you pointed straight into the relative wind...making you fly more efficiently and smoothly.

Treat the knot end of the string as a snakes head. Step on the snakes head with the rudder that it is pointed at. For example..if the tail of the snake is pointing to the right with its head at the left...step on that snakes head with left rudder as needed to straighten the tail so its coming right back at you.

Here is a picture of my Air Command landing on runway 18 at Mentone International last summer. You can see that the head of the snake needs to be stepped on with right rudder.....but NOT WHILE landing of course... ;D

[Brent_Brown]

test the EGT by heating water and use a cooking thermmomater put the prop in the water and see what you get.

[CLS447]

Stan,

So if you were going to do a fly by straight down that runway you would step on its head (right rudder) and fly down the runway somewhat sideways?

[StanFoster]

Chris: If I wasnt intending on landing but just wanted to fly the runway..then I would add right rudder..and bring the string straight back. This has the gyro flying straight into the relative wind which in the case of the Mentone picture...would have me flying down the runway with the nose to the right.

[GyroRon]

Isn't it weird that all of Tim C.'s pictures taken from his 447 powered Air command... Compaired to Chris' machine...... Chris is tracking straight and his rudder pedals are centered and Tim is going straight and yet his pedals are really offset.

[GyroRon]

Mentone looks so................................ Green! can't wait to go up this summer for a few days.

[CLS447]

Hey Ronnie, Maybe Tim is loppsided or he needs a string, man! That is wierd!

No , really it's me. I usually fly in the calm, so my winds are the ones I make by going forward. I guess you could say that I was never really comfortable with the old AC in any type of wind. I'm just over-cautious! In the calm I was totally in command.

When I would read Stan's posts about flying his AC in windy conditions I would think," Maybe I'm doin something wrong". Now we got that new guy- Tim O. out there flying the exact same machine in freezing, windy conditions while taking photos! (show-off).

I guess we all have different comfort level,& I know mine!

I can tell you this: After flying my new CLT AC, I know that this is the way for me to go! What a difference! No more waiting for those perfect nights & mornings. No more changing my shorts after hitting some thermals. Doug Reily felt the same way about his old 447, I think. I wouldn't recommend anything but CLT, especially to a beginner!

Thanks Stan I understand the string thing & will be using one on my new machine. Smoother & more efficiently are the key words, Right?

[Aussie_Paul]

Mceagle, Tim, you are so right re the trim string. If it is mounted on a vertical antenna, or someing that can be used for a pitch/attitude reference, you have the two most important instruments required for safe gyroplane flight.

Any time that the string is not in the center you are not flying as efficiently as id possible. In the early days this meant whether you stayed airborne or not!!!! I am sure a lot of the old timers will recal that!!!!

The only time that you do not keep the string in the middle is during late finals when you aim to keep the gyro straight.

Aussie Paul.

[StanFoster]

Chris: I can honestly say that my Air Command flew like a dream in any wind. The only thing I ever commented about it that was negative was flying perpendicular to the wind on gusty days. The pod I had on it would yaw back and forth. This had nothing to do with it not being CLT. It was just the pod was a bit much for even the extended tail.

I think flying relaxed is the main thing.

[cgmg]

Paul and John,

Today I switched the leads for my EGT gauges, and I have a 40 degree difference between the two. Switching the leads without adjusting the throttle cables now took a 80-100 degree temp difference between cylinders down to a 40-60 degree difference at typical cruising and takeoff rpms.

My next questions to the experts out there: I have an article by Roy Beisswenger from www. ultraflight.com detailing how to synchronize my carbs by using a telesoping bore gauge to measure the heights of the carb pistons at idle, and at 2/3rds throttle. I can borrow a gauge from a friend to perform this checkup. Should I just follow this procedure to get my carbs synchronized, and ignore whatever the temp differences are? At least with this procedure, each cylinder is getting the same amount of fuel, as well as can be expected with two carbs, one of which is new, and the other is about 7 years old.

One other item I checked today was the idle screw setting. The books call for 1/2 turn out for a 503. But at just 1/2 turn out, I am idling at 2600 rpm. To get my idle down to 2100, I had to turn them out about another 2 1/2 turns, with almost a turn's difference between the two to match up my egt's at idle.

To John in particular, you said you've done a lot of adjusting to your engine trying to balance your egt's, did you run across this same idle screw issue?

Again, thanks for all the help I hope to hear from this latest scenario with my engine.

By the way, should have ignored the weather report, and took the gyro back to the airstrip and did a little test flying today. Sounds like Friday may be my next best chance.

Mark

[GyroRon]

Your not turning the right screw! The idle screw that gets turned 1/2 a turn out on a 503 is the idle MIXTURE screw not the idle adjust screw.

The Idle mixture screw is a little screw on the side of the carb near the airfilter. It is on the lefthand side of the carb.

the idle adjust screw is the big screw with the spring between it and the carb body. all this screw does is sets the bottom level of the carb slides. The higher the slides the faster it runs. So idle speed is adjusted there. The idle mixture screw is for just mixture not setting Rpm.

At least this is the way I was told.....

[cgmg]

Ron,

You are correct. I am adjusting the idle set screw, not the idle mixture screw. As you can tell, I am still new at this engine setup stuff. I have not messed with the idle mixture screw, but guess I better check both of them to make sure they are the prescribed 1/2 turn out.

Thanks for pointing out the difference.

Mark

[gcrisler]

Using multiple size drill bits also works for synchronizing the carb slides.

[gyropilot]

Mark,

First, I would highly recommend you buy the Bing carburetor manual. It goes into great detail to explain the theory, operation, maintenance, and tuning of your carburetors. You can order it direct from Bing Vergaser. See their web site at: http://www.bingcarburetor.com/ for the telephone number / email address.

Second, when you tune your carb *on the ground* the EGT has nothing to do with it. The EGT reading is a tool to tell you if you have the correct jetting for cruise and full power settings. At lower RPMs the EGT reading is unreliable.

The idle mixture is verified by engine sound and RPM changes. The idle speed is checked by RPM alone.

The correct carb tuning basics are as follows:

Set the basic idle mixture and idle speed screws as recommended by Bing.
Insure the throttle cables are slack and some play exists in the cables when the carbs are at idle. You should be able to lift up slightly on the cables where they enter the top of the carburetor and feel the slack. This is important and you're verifying the carb slides sit on the idle speed screws and are not held open by the throttle cables.
Start and warm the engine.
Adjust idle speed and synchronize between the two carbs. While measuring the carb slide heights using various means (drill bits, telescopic gauges, etc.) is better than nothing, it's not the best way. The proper way to verify both engine cylinders are receiving the same air/fuel mixture is by using either vacuum gauges or an airflow meter. The later is what I use. You can buy one from J.C. Whitney online for $29.95 here: Carburetor Syncronizer (http://www.jcwhitney.com/webapp/wcs/stores/servlet/EndecaControllerView?D=88sc2792n&Dx=mode+matchallp artial&firstSearch=1&catalogId=10101&Nty=1&Ntx=mod e+matchallany&Dn=100010101+111&Ntt=88sc2792n&tmplf rame=EndecaCategoryView&langId=-1&section=body&storeId=10101&Ntk=AllTextSearchGrou p&ss=10101)
Adjust idle mixture. This is done by very *slowly* opening one idle mixture screw at a time. The engine rpm should initially increase and then if you continue to go far enough, it will start to run slightly rough. Open (unscrew) the mixture screw just until the idle speed is at it's highest and go no further. Close the idle mixture screw 1/8 turn. Repeat the same procedure on the other carb.
Readjust idle speed and synchronize between the two carbs again.
Recheck that you still have slack in the throttle cable with the engine at idle.
Increase engine speed to approx. 3000 rpm. The exact speed is not critical. At this point the carbs will be held open with the throttle cables and the idle speed screw is not a factor.
Synchronize carbs at this higher speed by adjusting the length of the throttle cables where they enter the top of the carburetors. Do not touch the idle speed or mixture screws for this operation as they have no effect.
Return the engine to idle, recheck to see you still have slack in the throttle cables at idle, and recheck the idle speed.
You're done!
Good luck,

John L.

[StanFoster]

Mark: Could you mention the name of the strip you fly off of? Or give me the GPS coordinates? Is it private or at an airport? When my 40 hours is flown off...I will be up to see you.

Thanks


Stan

[cgmg]

First to John,

Thanks for the wealth of info regarding tuning my carbs. I will order both the manual and the vacuum tool you mentioned. The article I used to set my carbs doesn't have anywhere near the detail you just gave me. I did just borrow a set of bore gauges, and it turns out I had the carbs dialed in pretty closely to each other. Unfortunately, I got home so late tonight I couldn't run the machine to do further testing. Hopefully this weekend I can follow your full procedures.

Next to Stan,

My airstrip is two private grass strips, called out on the Illinois Aeronautical Chart as Oltman and Schuck. I am actually hangared on the Schuck airstrip, and it's best if you use that airstrip. The owner of the Oltman strip is discouraging use of his strip for other pilots, but allows me to continue to use it since I am mowing it for him. The strips are located about 3 miles west of, and 1/2 mile south of, a little town called Minonk, which is on I-39 about 15 miles north of El Paso. Feel free to fly over and do touch and goes, or land to stretch your legs, any time. I naturally would prefer that you give me a holler, as I would love to see your machine, and do some formation flying with you.

Still tinkering with our machine, and waiting for a decent day for me to do some runway taxiis, and then a few patterns, to check my changes out.

Look forward to hearing from you.

Mark

I will send you the GPS coordinates some other time, can't find my GPS unit right now.

[cgmg]

Finally got my machine back to the airstrip Saturday. Checked everything over, put the blades on, and committed aviation.

Only flew for 20 minutes, but my CHT and EGT temps are now running within 5-10 degrees of each other, not considering that one gauge is reading 40 degrees higher than the other. This condition was just from using the bore gauge method of checking the carb pistons, still have to use John Landry's suggested method with the carb synchronization gauges.

The only remaining issue regarding temps is that the difference between cylinders is still outside of the spec limits at idle up to about 2500 rpm. As soon as I get above the 2600 rpm stage, the temps even out.

One other benefit of tuning the carbs is that I am now seeing an additional 300 rpm at full throttle. If this continues, I am going to have to reset the prop pitch. I've flown for the last two years at my current pitch, and never exceeded 6800 rpm.

Although I was only up for 20 minutes, it felt great! It's been just shy of three months since my last flight, and I forgot how much I missed it. Had a couple of cars stop on the road to watch me play around, probably wondering what that nut was doing on such a windy, blustery spring day. Didn't matter, I was smiling the whole time.

Mark

[StanFoster]

Mark: Glad to hear you are in the air. Thats a nice Air Command you have. I would like to fly over to your strip when I get my 40 hours flown off. What are your GPS coordinates..or the name of the strip if its on the aeronautical chart? Thanks...


Stan

[Caribean_gyro]

Mark
Question. what type of oil you have mineral ,synthetic or blend. This makes a temp and deposit issue. The carbons on the top of the cylinder can change the readings.

Now does this is a problem? No as far you are inside the engine parameters. I have run MC 72 and 90 HP, 503's and never got same reading. I focus my self to hev the lowest reading trade off as posible. Not too much gas or oil .

I have now a 180hp lycoming and she does the same I measure the 1 cylinder next to the prop and 1 next to the seat on the oposite side. Probes are the Super dupper Aviation type. they read 20 degreas diferent. So just swap probes to give you another data point so you know is wroking ok and go and fly safe

Chuck P