Rotax 503 DCDI Dual Carb Questions

CLS447

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1. Why are the intakes designed to tilt the carbs ? And why ?

2. Which direction should they tilt ?

The only place that I could find the following info was here.......

http://www.ultralightnews.ca/articles/enginesetup.htm



"Inverted installation problem with the Rotax dual carb 503 engines.
If you are using a dual carb 503 in an inverted installation you must turn the aluminum intake manifolds over - once again the engine was designed to run spark plugs up.

On the 503 dual carb the inlets - when the engine is upright have a slight upward incline. When you turn the engine over this incline is NOW down, which necessitates the removal of the intake, turning it 180 degrees and reinstalling it."

NOW....which way is the incline ????????????

Now let me see if I can post a drawing from the Rotax manual......

http://www.leadingedge-airfoils.com/pdf/503info.pdf

The sideways drawing looks to me as though the air filters are UP !!!
 
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CLS447

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Who would know the answers ?

They tilt those carbs for a reason & I want to know what it is !!!!!!
 

mceagle

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My guess would be that as the air flows through the carby, under the piston and then down into the crankcase, then a slight down slope would help the airflow, without having too much angle such that it could compromise the fuel mixture.
I suspect that it would also make it easier for excess fuel vapor to rise and escape rather than "flood" the engine.
 

scottessex

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I didn't see any 2 stroke injection kits on that site. :)
 

DennisFetters

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The 503 engine sits in the snowmobile at an angle to give more room for the exhaust system, so they designed the intake manifold at an angle so the carbs would sit level.

When they adapted the engine to aircraft use, they just kept the same manifold rather than make a new one, because it just didn't make much of a difference with the carbs sitting at that slight angle. Besides, the new jetting Rotax provided with the aircraft version compensated for the different float bowl level.

You can run the manifold with the carbs pointing up or down, makes no diffidence, just depends on how they fit best in your application.

Besides, aircraft have a tendency to fly at different angles anyway, carbs still work....
 

CLS447

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So....the 503 ALWAYS had angled intakes ?

Dennis, those were my thoughts...up or down. But LEAF said that the oil injection lines should enter the bottom of the intakes. That will always tilt the carbs air filters down whether the engine is inverted or not.

I am just looking for the facts.
 

DennisFetters

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So....the 503 ALWAYS had angled intakes ?

Dennis, those were my thoughts...up or down. But LEAF said that the oil injection lines should enter the bottom of the intakes. That will always tilt the carbs air filters down whether the engine is inverted or not.

I am just looking for the facts.

The only reason LEAF said that was in the theory that some of the oil in the little tubes would drip out some if they were on top. I have never had that happen, I think they just said it once to look smart. Sure, in theory, but in reality, its not enough to make any difference.
 

CLS447

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I am going to call the big 3 rotax guys again today & see what other BS they can come up with.

If this was that important , why is it not in the Rotax manual !!!!!!!!
 

scottessex

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Geeze Man, fire that sucker up already! It is not like it is going to the moon!
If you want to be Per-the-factory-rotax, just flip the intake and be done with it.
Otherwise just go with it. If it drips a drop of oil in the intake, big deal, it will burn off on start up.
If you would have mounted the engine upright..........

You know I am messin with you, but hey the carbs don't know the difference, just like Dennis said.
 

GyroRon

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Geeze Man, fire that sucker up already! It is not like it is going to the moon!
If you want to be Per-the-factory-rotax, just flip the intake and be done with it.
Otherwise just go with it. If it drips a drop of oil in the intake, big deal, it will burn off on start up.
If you would have mounted the engine upright..........

You know I am messin with you, but hey the carbs don't know the difference, just like Dennis said.

I 2nd that Scott....
 

CLS447

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I called everybody....I did not like the guy from CPS, he said to mount the intakes whichever way makes them the most level.

But it seems that there is no good reasons so.......I am leaving them the way I have them. Oil injection lines coming in the bottom of the intakes. Carbs tilted air filter down.

The only reason seemed to be to keep fuel from flowing into the cylinders by gravity.

I will be registering my engine warranty with LEAF.

I should be done with my wiring today. I will go over the whole gyro with a fine tooth comb & safety everything. Looks like sunshine on Sunday.....I hope to bring her to life on Easter Sunday.

One more question....IS ANYONE ON THIS FORUM FLYING WITH A 503 DUAL CARB WITH OIL INJECTION ??

I must be breaking new ground here !!!
 

DennisFetters

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One more question....IS ANYONE ON THIS FORUM FLYING WITH A 503 DUAL CARB WITH OIL INJECTION ??
I must be breaking new ground here !!!

Dual carbs with oil injection is the best way to go. More horse power with duel carbs, and jetting is not as sensitive to changing weather.
 

Edypaul

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I just installed Oil injection on my 503 duel carb. Havent flown it yet. Wish me luck!
 

DennisFetters

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I just installed Oil injection on my 503 duel carb. Havent flown it yet. Wish me luck!

It will be a better engine for it.

Oil injection is one of the best things to happen to Rotax aircraft engines. People that don't use it is simply behind times and do not grasp its importance.
 

CLS447

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Ed, how are your intakes tilted?

Did you buy the oil injection intakes or install the fittings in the exsisting intakes ?

Dennis, did the oil injection exsist when you made the Commanders ?
 

Edypaul

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Chris

My intakes are angled up. The oil injects from the bottom and my engine had the fittings installed. I have electric start so I had to buy a shorter gear input shaft to the pump. I bought the pump from Ernie. All i had to add was a tank and a cable from my throttle to the pump plus the lines and filter.
 

DennisFetters

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Dennis, did the oil injection exsist when you made the Commanders ?

No, not when I first started.

After they did come out with oil injection I was one of the very first to fly with one. It was love at first flight. My engines stared lasting longer, I was able to fly extended trips without carrying bottles of oil, and I was able to eliminate de-carbonizing completely.

My 582 went 800 hours without needing to do anything, even the plugs were the same. But I never ran it below 950F EGT's in cruse, and at a water temp of 160F. It would have gone more than 1000 if the flood of 1993 didn't destroy my Commanders.
 

DennisFetters

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I have blown 3 rotax 503 engines due to plastic shaft failing.

OK, why did they fail? Its certainly not a common problem other people have had. You had it 3 times, so what are you doing differently than everyone else in the world? Whatever that is, I would highly recommend that you don't do that. Or, if you don't know, better be finding out, and if you can't find out, stop flying it until you do.
 
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