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rayw

Joined: 18 Jul 2009
Posts: 25
Location: Wisconsin, Central

Posted: Wed Nov 18, 2009 3:06 pm Post subject: Rotax 503

Hello,



I could use some help. I am running out of idea's. I have a 503 with dual Bing 54 carb's. The engine starts and runs well up to about 2000 RPM. After this RPM it has nothing left it just bogs. I have gone through both carbs so many times I could do it in my sleep. I don't think it is a fuel pump problem because I have rebuilt it and I have used the primer bulb to try to compensate for a potentially bad pump but this has no effect. The other day I ran it up to a point just before it bogged and put three fingers in front of the inlet of the right carb and got it to bog. I put three fingers in front of the inlet on the left carb and got a 1000 RPM rise. The carb on the left is an older type so I bought a brand new carb. Would you believe it? Same exact reaction. I went through the timing but I will probably go through it again to double check. Any body got any idea's? I have done so much that I can't even remember it all. 



Ray W.

joeing701(at)internet.is
Guest

Posted: Thu Nov 19, 2009 2:45 am Post subject: Rotax 503

Hello Ray.



How many hours do you have on the engine? When were the seals replaced?



Just some things to check. Air-leaks, Check if the rubber between carb  

and engine does not have any cracks. Seals, intake and exhaust  

manifold gaskets.

Have you done any adjustments to the propeller?  Check that the spark  

plugs have the correct gap adjustments.

Make sure that the jet needle is installed correctly, i.e. under  

plastic cup.



I would mostly suspect an air leak.



Hope this helps.



Regards,

Johann G.



On 18.11.2009, at 23:06, rayw wrote:



 	  Quote: 	
		   



 Hello,



 I could use some help. I am running out of idea's. I have a 503 with  

 dual Bing 54 carb's. The engine starts and runs well up to about  

 2000 RPM. After this RPM it has nothing left it just bogs. I have  

 gone through both carbs so many times I could do it in my sleep. I  

 don't think it is a fuel pump problem because I have rebuilt it and  

 I have used the primer bulb to try to compensate for a potentially  

 bad pump but this has no effect. The other day I ran it up to a  

 point just before it bogged and put three fingers in front of the  

 inlet of the right carb and got it to bog. I put three fingers in  

 front of the inlet on the left carb and got a 1000 RPM rise. The  

 carb on the left is an older type so I bought a brand new carb.  

 Would you believe it? Same exact reaction. I went through the timing  

 but I will probably go through it again to double check. Any body  

 got any idea's? I have done so much that I can't even remember it all.



 Ray W.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 73620#273620

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Nov 19, 2009 5:50 am Post subject: Re: Rotax 503

Your three finger test tells me that that one carb may be lean and the other rich. If you are absolutely certain that you have the correct jets and needles and clip locations in both carbs, then make sure that both carbs are open the same amount at idle and that they start opening simultaneously when advancing the throttle control. 



I just did a Bing 94 carb inspection for a customer and the internals were perfect but it turns out his linkage was not installed correctly and the idle speed was set too high which was causing him hard starting in cold weather. My point is that it is not always the internals that cause the problems. Sometimes it is the controls being not quite right. 



http://riddletr.googlepages.com/a%26pmechanix

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

williamtsullivan(at)att.n
Guest

Posted: Thu Nov 19, 2009 9:08 am Post subject: Rotax 503

Is it possible that he just has a broken throttle cable?

  

                                       Bill Sullivan

                                       Windsor Locks, Ct.

                                       Kolb Firestar, 447

 [quote][b]

ptag.dev(at)tiscali.co.uk
Guest

Posted: Thu Nov 19, 2009 9:09 am Post subject: Rotax 503

Hi! Ray

I'm no specialist but I'd look for a plug lead which has deteriorated.

Have you for instance verified that all plugs are good?

Regards and good luck

Bob Harrison Europa G-PTAG Rota 914



--

Blumax008(at)aol.com
Guest

Posted: Thu Nov 19, 2009 11:24 am Post subject: Rotax 503

In a message dated 11/19/2009 12:10:07 P.M. Eastern Standard Time,  ptag.dev(at)tiscali.co.uk writes:

  	  Quote: 	
		  I don't    think it is a fuel pump

problem because I have rebuilt it and I have used    the primer bulb to try to

compensate for a potentially bad pump but this    has no effect. 	


 

 Tell me about it! I'm currently having hell with a bogging 503 myself that  was showing lots of air bubbles in the fuel lines from the pump on to the carbs.  We've done everything from changing both carbs out (before we saw the bubbles in  flight)...to no effect...to changing the fuel pump & its' location &  back...to no effect...and a myriad of other what-we-thought were  fixes. We did find an exposed pick-up wire that had rubbed itself raw  & was shorting out against a CHT lead. We fixed that...to no effect.

  

 FINALLY...(we think)...we ran all new fuel lines from the fuel tank to  the pump to the carbs. We also elimated two in-line fuel  filters that were between the fuel pump & the carbs. Now we only  have the one filter just outside the fuel tank. SO FAR - SO GOOD. Flew it  yesterday & all is well...but I ain't holding my breath. 

  

 We do know it was not electrical in nature...stator, rotor or  pick-ups...but that exposed pick-up wire (mentioned above - in combo with  the fuel flow problem) may have contributed to a complete engine  failure a week ago. Landed safely.

  

 What you might try doing is installing a "T" in your fuel line from the  pump to the carbs. Disconnect what you think is the bad fuel pump line & T  it into the good fuel pump line. Of course close off the old line with tie wrap  & fuel line. See what happens.

  

 Bottom line...be careful. Think safety. Stay in the pattern until you know  for sure it's fixed. Saved my ass the other day.

  

 Bill Catalina

 Tallahassee, Florida

  [quote][b]

rayw

Joined: 18 Jul 2009
Posts: 25
Location: Wisconsin, Central

Posted: Sat Nov 21, 2009 10:49 am Post subject: Re: Rotax 503

First of all I want to thank those that replied. Every idea I received gave me something to consider. Here is where it's at today:



After running up to 1500 RPM. I used a can of starting fluid and sprayed every nook and cranny. Pretty much every where except in the carb inlets (ok just a little to see what would happen)(It bogged). I heard no change at all other than that. When I wasn't spraying I was watching CHT's and EGT's. CHT's could not get warm enough to even get into the green. EGT's could barely get in the green if I ran up to 2000 RPM and let it go for awhile. Sounds like a very rich condition yes???



Now for a little back ground: I bought this airplane from a couple of good ol' boys in St. Joe, MO. (That is a story in itself). Now mind you I have nothing against good ol' boys from St. Joe......... When I got it home and got down to details. I found a lot of things not acceptable to me.  I have never heard it run or saw it fly. Normally a red flag but I got it so cheap I couldn't pass it up. My wife would argue but I still think it was worth it. Any way enough rambling. 



Both carbs have main jets = 158, Idler jet = 45, Needle jet = 2.7, Jet needle = 11K2. The top ring of the needle has the O-ring and the clip right under it on the second ring. The air screw is at .5. The floats arms are level when the carbs are upside down. I believe I have the recommended 1/2 inch of space between the top of the float bowl and the gas level in the bowl. 



Altitude at Stevens Point, WI (5 miles away) is 1050 ASL. The three finger test mentioned in my last post still has me scratching my head. It tells me that the carbs are still different in some way. Is a K&N air filter considered a "silencer"?



Thanks every one,



Ray W.

rparigor(at)suffolk.lib.n
Guest

Posted: Sat Nov 21, 2009 11:14 am Post subject: Rotax 503

Hi RayI'm a dinosaur, but remember in early 80s someone had what sounds like the exact problem you are describing on a Cayuna 2 cylinder I think with 1 carb for both cylinders, it was air cooled. Owner was supposedly a crackerjack mechanic and was trying to solve for some time. I fooled with for a short time and descided to do a thumb in spark plug test, one cylinder was dead, hole in piston. Sorry I am unfamiliar with 503, don't know if it has one or 2 carbs.Did you check compression?Ron Parigoris   [quote][b]

occom

Joined: 26 Aug 2006
Posts: 404

Posted: Sat Nov 21, 2009 12:10 pm Post subject: Rotax 503

I'm going to toss in these two really silly questions. 1)There is a prop on 

this set to provide a load? and 2) you have checked the gap on the plugs and 

none of them are even a tiny bit more than specified?



The reason I ask is that engines get way weird without the proper load, and 

the coils on these are not particularly powerful, wide gaps are a bad idea.

---

joeing701(at)internet.is
Guest

Posted: Sat Nov 21, 2009 1:06 pm Post subject: Rotax 503

Hello Ray.



One thing to look into. The tube from the crank to the fuel pump. Make  

sure that it is not from a thin wall tube and not too long. If so, it  

could clamp together and prevent the fuel pump to suck enough fuel to  

the carbs.

It could also be leaking.

Check it out, it is rally easy and cheap to fix.



Hope this helps,

Regards.

Johann G.





On 21.11.2009, at 18:49, rayw wrote:



 	  Quote: 	
		   



 First of all I want to thank those that replied. Every idea I  

 received gave me something to consider. Here is where it's at today:



 After running up to 1500 RPM. I used a can of starting fluid and  

 sprayed every nook and cranny. Pretty much every where except in the  

 carb inlets (ok just a little to see what would happen)(It bogged).  

 I heard no change at all other than that. When I wasn't spraying I  

 was watching CHT's and EGT's. CHT's could not get warm enough to  

 even get into the green. EGT's could barely get in the green if I  

 ran up to 2000 RPM and let it go for awhile. Sounds like a very rich  

 condition yes???



 Now for a little back ground: I bought this airplane from a couple  

 of good ol' boys in St. Joe, MO. (That is a story in itself). Now  

 mind you I have nothing against good ol' boys from St. Joe.........  

 When I got I home and got down to details. I found a lot of things  

 not acceptable to me.  I have never heard it run or saw it fly.  

 Normally a red flag but I got it so cheap I couldn't pass it up. My  

 wife would argue but I still think it was worth it. Any way enough  

 rambling.



 Both carbs have main jets = 158, Idler jet = 45, Needle jet = 2.7,  

 Jet needle = 1K2. The top ring of the needle has the O-ring and the  

 clip right under it on the second ring. The air screw is at .5. The  

 floats arms are level when the carbs are upside down. I believe I  

 have the recommended 1/2 inch of space between the top of the float  

 bowl and the gas level in the bowl.



 Altitude at Stevens Point, WI (5 miles away) is 1050 ASL. The three  

 finger test mentioned in my last post still has me scratching my  

 head. It tells me that the carbs are still different in some way. Is  

 a K&N air filter considered a "silencer"?



 Thanks every one,



 Ray W.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 74101#274101

rayw

Joined: 18 Jul 2009
Posts: 25
Location: Wisconsin, Central

Posted: Sat Nov 21, 2009 7:20 pm Post subject: Re: Rotax 503

Hello,



I cannot seem to find a Rotax 503 repair manual for purchase. Does any one know of a source. It would be nice to know things like bolt torque specs and pattern, plug gap, acceptable cylinder compression etc.



I did a compression check and got 115 front and back. The plug gap should be ok because the plugs are brand new. The prop is bolted on and is providing a suitable load. All fuel lines are brand new including the impulse line for the fuel pump. The impulse line is 6 inches long and was ordered from LEAF specifically for this purpose. The entire fuel system is brand new. This airplane did not even have a fuel tank when I bought it. 

It is an older engine with points ignition. I was told the engine has 160 hours. Both slides are reacting the same when responding to the throttle.



Thanks every one!!



Ray

ptag.dev(at)tiscali.co.uk
Guest

Posted: Sun Nov 22, 2009 2:03 am Post subject: Rotax 503

Hi! Ray 

If it is a points ignition have you tested the condenser?

Regards

Bob Harrison   Europa G-PTAG



--

occom

Joined: 26 Aug 2006
Posts: 404

Posted: Sun Nov 22, 2009 2:52 am Post subject: Rotax 503

Never assume the plugs are gapped properly because they are new, in fact 

it's likely they aren't.



---

dougsnash

Joined: 14 Apr 2008
Posts: 281

Posted: Sun Nov 22, 2009 6:22 am Post subject: Rotax 503

 	  Quote: 	
		   It is an older engine with points ignition. I was told the

 engine has 160 hours.


	


Check the crank seal behind the points, this sounds kind of like a bad crank seal.



As for the service manuals, they are available for free from the rotax owners site www.rotax-owner.com



One more thing to check is the internal condition of your exhaust.  Remember, on two stroke engines, the muffler can is just as important as the carburetor for proper running.  I had a muffler come apart inside and couldn't generate enough power to get into the air.



Do Not Archive



Doug MacDonald

Zenith CH-701 Scratch builder

Former Skyseeker MKII pilot

      __________________________________________________________________

Looking for the perfect gift? Give the gift of Flickr! 



http://www.flickr.com/gift/

Blumax008(at)aol.com
Guest

Posted: Sun Nov 22, 2009 7:23 am Post subject: Rotax 503

In a message dated 11/21/2009 4:06:59 P.M. Eastern Standard Time,  joeing701(at)internet.is writes:

  	  Quote: 	
		  The tube    from the crank to the fuel pump. Make  

sure that it is not from a    thin wall tube and not too long. If so, it  

could clamp together and    prevent the fuel pump to suck enough fuel to  

the  carbs.

	


 

 My thought exactly! Back in '79 I had an old Yamaha 18hp single lunger on  an old Quicksilver weight shift. I put a new "Ace Hardware Store" clear plastic  fuel line on it...impluse line to fuel pump...it was so weak that when  power was applied, it would actually shrink in size, cut down on fuel flow &  engine would bog or go to high temps...or both. 

  [quote][b]

rayw

Joined: 18 Jul 2009
Posts: 25
Location: Wisconsin, Central

Posted: Sun Nov 22, 2009 3:59 pm Post subject: Re: Rotax 503

Hello,



As soon as I wrote that the plugs were new and should be ok I knew I was gonna' catch it. Rightly so.........My High school shop teacher would have smacked me for that comment. 



I just went out and checked them. They are far in excess of .015/.019. I did not close them up yet or run the engine but I am going to feel super silly if this is the trouble.  Oh yeah.....With the plugs out I did another compression test. I got 112 in back and 120 in front. Seems low..Is it?

rayw

Joined: 18 Jul 2009
Posts: 25
Location: Wisconsin, Central

Posted: Sun Nov 22, 2009 6:00 pm Post subject: Re: Rotax 503

Is anyone on this list from UK, Ireland or Iceland?



Thanks,



Ray W.

Johann G. Johannsson

Joined: 10 Jan 2006
Posts: 18
Location: Iceland

Posted: Mon Nov 23, 2009 12:23 am Post subject: Rotax 503

Hello Ray.



Yes, I am from Iceland.



Best regards,

Johann G.



On Sun, 22 Nov 2009 18:00:55 -0800, "rayw" <rmwis(at)charter.net> wrote:

 	  Quote: 	
		   

 

 Is anyone on this list from UK, Ireland or Iceland?

 

 Thanks,

 

 Ray W.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p 74358#274358

_________________
Johann G.
Iceland.
Flying Zenith 701.

ptag.dev(at)tiscali.co.uk
Guest

Posted: Mon Nov 23, 2009 5:00 am Post subject: Rotax 503

Hi!

The real test for compressions should give you the best engine health 

test,

that is to say  a compression drop test .   Have you done a propper 

comparrison compression drop test ?

You would be allowed a maximum of 25% loss over perfect starting at 80 

psi. Watch your head doing it because if the prop gets away from top 

dead centre  it will damage your head!

Regards

|Bob Harrison G-PTAG Europa 914



 	  Quote: 	
		  ----Original Message----

From: rmwis(at)charter.net

Date: 22/11/2009 23:59 

To: <rotaxengines-list(at)matronics.com>

Subj: Re: Rotax 503






Hello,



As soon as I wrote that the plugs were new and should be ok I knew I 

was gonna' catch it. Rightly so.........My High school shop teacher 
	


would have smacked me for that comment. 

 	  Quote: 	
		  

I just went out and checked them. They are far in excess of .015/.

019. I did not close them up yet or run the engine but I am going to 
	


feel super silly if this is the trouble.  Oh yeah.....With the plugs 

out I did another compression test. I got 112 in back and 120 in front. 

Seems low..Is it?

 	  Quote: 	
		  



Read this topic online here:



http://forums.matronics.com/viewtopic.php?p 74344#274344




	






The latest news as it happens - http://www.tiscali.co.uk/news

matronics(at)bob.brennan.
Guest

Posted: Mon Nov 23, 2009 5:52 am Post subject: Rotax 503

I am from the UK, moved to the US, flying a Kitfox II built in the UK -

what's your real question Ray?



Bob Brennan - N717GB

ELSA Repairman, inspection rated

1991 UK Model 2 ELSA Kitfox taildragger

Rotax 582 with 3 blade GSC prop

Wrightsville Pa



--

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