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Carb Balance

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Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Fri Oct 09, 2009 4:32 am Post subject: Carb Balance

This question is probably for Roger but some others may be interested.  Do I have to go through the whole mechanical and dynamic balance each time I balance the carbs on my 912uls or can I just do the dynamic step.  Seems after once doing the mechanical setup, you shouldn't have to do it again.



thanks 

Rich in

North Idaho

 Kitfox SS7

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rlborger(at)mac.com
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Posted: Fri Oct 09, 2009 5:08 am Post subject: Carb Balance

Rich,



You probably should check the mechanical setup at both idle and full throttle to ensure both carbs reach the stops and that correct idle is set.  Only adjust if necessary prior to dynamic balance.



Other folks please chime in...



Bob Borger

Europa XS Monowheel, ROTAX 914 with intercooler & Airmaster C/S prop.



 

On Friday, October 09, 2009, at 07:32AM, "Rich L" <kitfox812(at)gmail.com> wrote:

 	  Quote: 	
		  



This question is probably for Roger but some others may be interested.  Do I have to go through the whole mechanical and dynamic balance each time I balance the carbs on my 912uls or can I just do the dynamic step.  Seems after once doing the mechanical setup, you shouldn't have to do it again.



thanks 

Rich in

North Idaho

 Kitfox SS7





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http://forums.matronics.com/viewtopic.php?p 67209#267209

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Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Fri Oct 09, 2009 7:01 am Post subject: Re: Carb Balance

Hi Rich,

You really should do both a mechanical and then a pneumatic each time. The reason behind this is things can change a little like cable length from newer cables relaxing and a slight stretch to ends slipping some in the cable locks. If you hook up your gauges and the carbs are close to being together then in reality it would most likely be ok, but I will tell you Rotax wants the mechanical balance done each time before the pneumatic. Carbs should be balanced every 100 hrs and at the annual condition inspection. I have never seen a set of carbs balanced when I hook up a set of gauges and they never will because of normal wear & tear on tolerances within the carb and on the linkages outside. Once you have done it a time or two then the carb balance procedure gets easier. This is one the single most important things you can do for you engine's health. The cross over tube can only correct so much then the right side of the engine will try to run at a different rpm from the left if the balance is out too far. This makes one half the engine working against the other and causes vibration and wear and tear on the engine internals and gearbox. A gauge set does not have to be expensive and you can make your own if you want. I do lots of 100 hr and annual inspections. When I do the 100 hr. I just reset the annual date so someone doesn't have to do two or more inspections a year depending of course on how many hours a year they fly. If they fly 200-300 hours a year then extra inspections are needed. Many SLSA have to do regular 100 hr. inspections required by the Mfg. and that experimental's aren't really required to, but Rotax wants you to do 100 hr. inspections regardless of what type of plane you fly. If you skip maint. times then you only hurt yourself and may set yourself up for later expenses for maint issues. With out the maint checks how can you guarantee your plane is in good condition and that something might fail or something is coming loose? I know even with the inspection it is not 100%, but it's a whole lot better than no inspection or regular service. I know a few backyard mechanics with their planes that think so long as it doesn't quit and starts it is ok to fly!

The biggest problem that Rotax engines have whether 2 stroke or 4 stroke are the owners. Either no maint or trying to change something.

To answer your question: Can it be done, yes, but you should do both.

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Tucson, Az.
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Light Sport Repairman
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Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Fri Oct 09, 2009 7:35 pm Post subject: Re: Carb Balance

The engine was running like a top but I had 130 hours since changing plugs and carb balance and it was annual anyway.  I just bought a Carbmate and watched the video on ROAN so I was ready.  I changed all the plugs and hooked up the Carbmate and it showed the carbs a little out of balance till the engine wormed up, then it was in balance without touching anything.  I put it to full sense and it still showed in balance.  I double checked the Carbmate connections.  I can't see detuning to retune when its ok.????????



Rich

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Sat Oct 10, 2009 7:26 am Post subject: Re: Carb Balance

 	  Rich L wrote: 	
		  The engine was running like a top but I had 130 hours since changing plugs and carb balance and it was annual anyway.  I just bought a Carbmate and watched the video on ROAN so I was ready.  I changed all the plugs and hooked up the Carbmate and it showed the carbs a little out of balance till the engine wormed up, then it was in balance without touching anything.  I put it to full sense and it still showed in balance.  I double checked the Carbmate connections.  I can't see detuning to retune when its ok.????????



Rich 	




Er, yeah, if it ain't broke, don't fix it . Course, that's what routine maintenance is all about, finding what's busted but also what's not .



For example, a friend of mine here had sent off his carburettors (912ULS) to be rebuilt a few months ago. To the tune of about $400 they came back nice and shiny new looking. But when put back on the engine, the balance would go way way off as the throttles where opened. He could only get good carb balance at full throttle or at idle. When they were balanced at idle, tho, the engine was idling very very rough, with one side even popping and backfiring.



He later discovered the idle jet on one of the carbs was still plugged with varnish.... again, that's after a $400 rebuild of both by a well-known Rotax dealer!



He cleaned the jet with carburettor cleaner and after that balancing was easily done and they stayed very close throughout the throttle range.



Caveat Emptor! (and I need to check my balance too ASAP).....



LS

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Sat Oct 10, 2009 7:29 am Post subject: Re: Carb Balance

[quote="lucien"] 	  Rich L wrote: 	
		  The engine was running like a top but I had 130 hours since changing plugs and carb balance and it was annual anyway.  I just bought a Carbmate and watched the video on ROAN so I was ready.  I changed all the plugs and hooked up the Carbmate and it showed the carbs a little out of balance till the engine wormed up, then it was in balance without touching anything.  I put it to full sense and it still showed in balance.  I double checked the Carbmate connections.  I can't see detuning to retune when its ok.????????



Rich 	




Er, yeah, if it ain't broke, don't fix it . Course, that's what routine maintenance is all about, finding what's busted but also what's not .



For example, a friend of mine here had sent off his carburettors (912ULS) to be rebuilt a few months ago. To the tune of about $400 they came back nice and shiny new looking. But when put back on the engine, the balance would go way way off as the throttles where opened. He could only get good carb balance at full throttle or at idle. When they were balanced at full throttle, the engine was idling very very rough, with one side even popping and backfiring. The Carbmate showed one side completely pegging the scale at idle.....



He later discovered the idle jet on one of the carbs was still plugged with varnish.... again, that's after a $400 rebuild of both by a well-known Rotax dealer!



He cleaned the jet with carburettor cleaner and after that balancing was easily done and they stayed very close throughout the throttle range.



Caveat Emptor! (and I need to check my balance too ASAP).....



LS

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LS
Titan II SS

Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Sat Oct 10, 2009 11:05 am Post subject: Re: Carb Balance

OK, I stand humbly corrected.  I will do the complete balance. Thanks for the inputs.



Rich

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