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Buckaroo

I wanna cancel the need to balance my carbs and I’ve heard of a solution very interested!!

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Someone told me there’s a solution to the need of carb balancing. That’s replacing the tubing between each carb with a larger diameter piece. 

Can someone please elaborate! I’m very interested and if true why isn’t it a popular mod? 

Thanks 

Buckaroo 

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Because it's covering up the real problem. Inbalanced carbs.

The only thing that this will accomplish is shifting the bulk of the load from one carb to another. They're also not designed to be able to carry fuel from one intake to the other. You'll end up with a leaner mixture because the charge will have to travel further to the cylinders on the higher vacuum side.

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1 hour ago, Anticept said:

Because it's covering up the real problem. Inbalanced carbs.

The only thing that this will accomplish is shifting the bulk of the load from one carb to another. They're also not designed to be able to carry fuel from one intake to the other. You'll end up with a leaner mixture because the charge will have to travel further to the cylinders on the higher vacuum side.

Yes,  but at the lower rpm’s where we operate only a small amount of time ie. idle, warm up etc. this is where the imbalance is most harmful. At higher rpm’s carb balance is not a issue unless of course they are way off. Please explain!

 Thanks 

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Leave what you have. Some have tried it and they say they like it. The tube isn't really in play after approximately 3500 rpm anyway. That's also why it's better to sync the carbs up around that rpm because that is where you spend most of the time (above 3500) and the tube goes out of play as you increase throttle past that. So it would only affect the lower rpms. Most things you read on the internet by a few people is best left alone.

When you read some of these things ask yourself how a few people are smarter than all the Rotax engineer's, smarter than all the factory test time since the 1920's, smarter than 50K engines on the market and smarter than over 5 million run hours. Not one of these few have any test equipment, none do any extend testing that includes thousands of hours, none usually have an engineer's education. Rotax has a reason for doing things. If you don't know what and why better leave things alone.

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Here! Here!

In he current issue of EAA magazine the Rainbow Aviation folks said some people had shortened the actuation shafts on Rotax fuel pumps thinking they were going to make them work better. Yikes!

Mike Koerner

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6 hours ago, Buckaroo said:

Yes,  but at the lower rpm’s where we operate only a small amount of time ie. idle, warm up etc. this is where the imbalance is most harmful. At higher rpm’s carb balance is not a issue unless of course they are way off. Please explain!

 Thanks 

 

Now imagine trying to idle. If the carbs are imbalanced, you will get one side that doesn't sit on the idle stop, while the other cable is tight as a piano string.

A larger crossover tube would indeed smooth things out for longer, but it won't solve the problem of imbalanced carbs. Little incosistencies in the carbs, temperatures outside, cable routing, these all contribute to carbs falling out of sync. I usually only end up with carbs a couple inches out of sync in extreme cases. Even applying a twisting force on the throttle arm while tightening the nut will change syncrhronization, as there is a very slight play in the keyed hole.

Roger: for those at low altitude I agree, it becomes very insignificant. Those on decent and operating at high altitude wouldn't fare so well.

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Hi Corey,

Adjust the needle for people that live and fly at high altitudes.

The Balance tube isn't affecting much a high rpm and altitudes. The butterfly in the carb throat is open too far. Rotax says once the rpm hits 3500 and keeps climbing the balance tube plays almost no part.

Unless someone is a aeronautical engineer, has computer data and lengthy test on a dyno I'll have to go along with Rotax.

Anything I would hear from an individual that said this helped would be just hearsay and speculation without data to back it up. I have seen it way to many times with claims about props, wheel pants and other mods that customers think they are getting much better performance. If you believe something bad enough it must be true?

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6 minutes ago, Roger Lee said:

Hi Corey,

Adjust the needle for people that live and fly at high altitudes.

The Balance tube isn't affecting much a high rpm and altitudes. The butterfly in the carb throat is open too far. Rotax says once the rpm hits 3500 and keeps climbing the balance tube plays almost no part.

Unless someone is a aeronautical engineer, has computer data and lengthy test on a dyno I'll have to go along with Rotax.

Anything I would hear from an individual that said this helped would be just hearsay and speculation without data to back it up. I have seen it way to many times with claims about props, wheel pants and other mods that customers think they are getting much better performance. If you believe something bad enough it must be true?

All the reply’s sound logical so I’m abandoning any idea of doing this!

Now I hear that the ZIPPER KIT when installed eliminates the need for carb balance. Is this true and if so how does this work?

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Why the back bends to get rid of carb balance?  I do it about twice a year and it takes less than ten minutes once you’ve done it a couple of times.

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9 hours ago, FlyingMonkey said:

Why the back bends to get rid of carb balance?  I do it about twice a year and it takes less than ten minutes once you’ve done it a couple of times.

This is true! My thinking was earlier in my post that if a simple larger radius balance tube would eliminate the need for carb balance then why not do it! Simple as that. But now reading these posts I agree that the engineers at Rotax would of developed this early on. So with that in mind doing it the standard way in fine with me. 

I have come to the conclusion that modding these wonderful engines with turbo’s, zipper kits etc. is only going to get you gremlins in the end. 

Its fun for me to throw stuff out on this forum to hear the replies plus you learn a lot! ?

My engine is bone stock and it’s staying that way!

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A larger tube would not exclude a carb sync. The carb cables will stretch, the internal parts will wear. The tube will only compensate at lower rpms and only so much. Carb syncs would still need to take place. The carbs have to open equally as they progress in opening towards full throttle and when you're in cruise rpm. 

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21 minutes ago, Roger Lee said:

A larger tube would not exclude a carb sync. The carb cables will stretch, the internal parts will wear. The tube will only compensate at lower rpms and only so much. Carb syncs would still need to take place. The carbs have to open equally as they progress in opening towards full throttle and when you're in cruise rpm. 

Makes sense now! Thanks for the clarification!

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You would lose power and performance. Dual carbs is what gets it to 100 hp.

In the older days :) (early 1980's) the Cuyuna 30 hp 2 stroke had a single carb. They went to 2 carbs and better air intake and it went to 40 hp.

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I wonder if a design could be made that was essentially two carbs with an internal vacuum balancing crossover, that operated off a single cable.  So you'd get the benefits of a single carb, without needed to change the sync.  The only downside I see:

1) You can't use cheaper off-the-shelf Bing carbs; Rotax would have to engineer & build it.

2) The runners to the cylinders would probably be a little longer.

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If I was exp.I would build and design the same setup as motorcycles have then

they would most likely never need to be sync. or at least not very often. I actually

have the parts off some old cycle carbs. to do it. also a cable

with a knob to adj idle . It would work great. Maybe one day I'll go to dark the

side.

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My old 1974 Honda 750 had 4 carbs to be synced, but not too often and I know BMW used Bing's and they needed to be synced.

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To be quite honest, we sync carbs far more than I think our airplanes actually need. But, we're also talking about airplanes here. Difficulty syncing carbs has, in my personal experience, helped to identify issues long before they became actual issues. It's hard to sync carbs when there's a problem developing. As a result, I often fix issues before they scare the pants off customers.

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4 hours ago, Mike Koerner said:

Mine have not been synced in over 3 1/2 years (478 hours). I'm waiting for the "SYNC" light to come on.

Mike Koerner

Ok I’ll bite! Please tell me about the SYNC light? ?

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I had my mechanic adjust idle to 1800 without syncing carbs ( he has been in Rotax business since late 90s ) and now the engine is slightly rough in the midrange ( between 2400 and 4000) while remaining smooth in cruise or at full power. I am assuming carbs are out of balance and I just ordered CarbMate and will attempt to do balance the damn carbs for the first time ?

I went for Rotax maintenance course last year so I do remember some things and between that and various videos and materials on the web, I think I should be able to manage that...

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Any time you adjust a carb you MUST put a sync tool on because one carb may be influencing the idle or high rpm more than the other and without a sync tool on you have ZERO way to know which one. If a mechanic says he's been doing this for 30 years and can tell just by hearing it. Then go find a new mechanic.

Bill,

Send that Carbmate back. Use gauges. None of the experts I know use an electronic device. You can not diagnose with them. The gauge s are cheaper to buy. When you hook up a set of gauges I can tell you in the first 15-30 seconds if the the carbs can even be synced in their present state, if carb cables need to be lengthened or shortened on the throttle arm, which carb needs to be adjusted and by how much at higher rpms, which carb at idle needs to be adjusted, if the carb idle jet is clogged, ect... You can not do all that with an electronic sync tool. Using the electronic device takes twice as long to sync the carbs.

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I agree Roger I would never make an adjustment without a balancer connected. Cable tension and the condition of those flimsy idle stops have an effect on the screws so that 1/20 of a turn on one carb can have a different effect than a 1/20 on the other. So the old “I’ll just turn them the same amount” isn’t very accurate. One thing I’ve found that really helps is putting a double heat shrink at the point where the cable sheathing enters the brass adjuster on the carb. Keeping that connection from flexing really helps keep every synced over time. Also never remove or adjust a carb when the lever in the cockpit is at idle, it almost always tweaks ones of the stops. Move the lever to half throttle and release  the tension. Then you can pop a carb out and check a float bowl or whatever and you’ll be pretty close when you put her back in place. 

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30 minutes ago, Jeremy MacGregor said:

Also never remove or adjust a carb when the lever in the cockpit is at idle, it almost always tweaks ones of the stops. Move the lever to half throttle and release  the tension. Then you can pop a carb out and check a float bowl or whatever and you’ll be pretty close when you put her back in place. 

That's a great tip. Thank you.

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